This

In all cases only half an ounce of baryta solution was used. Minimetric House and Workshop Method.This method is partly described in the report on the air of mines, and long tables given. There were shown two modes of using it-first, with baryta water; second, with lime water. Suppose we desire to know if the air contains more than 0.04 per cent. of carbonic acid, we fill a bottle containing 5:422 oz. with air by pumping as elsewhere described, with a little finger pump, and shake it in half an ounce of baryta water. If there is any precipitate at all, the amount of carbonic acid in the air is above 0:01 per cent. would indicate that the air is less pure than outside. If we allow 0.06 per cent. of carbonic acid in a room, we take a bottle of the size of 3.6+0.5oz. 4·1 oz., or 116·23,c.c., and if, after a trial as before we find a precipitate, however small, or a decided, although slight milkiness, the air is deteriorated beyond 0:06. This relates to dwelling-houses. If for workshopsp.c. (0.25) is allowed, a bottle of 0 867 +0.5 oz. 1.367 oz. or 38.744 c.c. is sufficient. This could go into the waistcoat pocket. If 05 or per cent. is permitted,a bottle of 0.433 +0.5 oz. is enough 0.933 oz. or 26 475 c.c. This amounts to nothing more than shaking an ounce bottle. The addition of half an ounce is for the baryta water.

The lime water method will probably be adopted more usually, as lime is so common. The experiment is exactly the same as with baryta water, but larger bottles are required.

ditto

0.06 carbonic acide in the air gives no precipi; tate or milkiness when oz. of lime water is added to a bottle of the air containing............109 oz. (=309 cub. cent.) 2.997 oz. (=84-958 cub. c.) ditto 1748 oz. (=49.564 cub. c.) The author said that by this simple method the greatest refinement could be attained.

0.25 ditto 0.5 ditto

NON-EXPLOSIVE GUNPOWDER.

maly of a built-up gun without a single weld in it. It is understood that a gun on this plan will shortly be commenced. We hope the most sanguine expectations of Mr. Ericsson may be realised in the construction of a gun strong enough to project a spherical steel shot, with 100 lbs. of powder. Mr. Ericsson is working in the right direction. Strength, endurance, calibre, are the essentials of the "coming" gun.

In spite of this exposure, the grains of gun-
powder were as hard, and the combustion as
rapid and complete, as if they had just come
from the corning mill. It is true that the bulk
and weight of the mixture are three times as
great as that of the gunpowder itself, but it can
be stored in bulk in very little if any greater
space than is required by gunpowder in barrels;
and, as regards the question of carriage, there
is no doubt that, for commercial purposes, three
tons of the non-explosive compound would not
cost so much as one ton of gunpowder. Mr. ON THE CONSTRUCTION AND WORKING
Gale has been ordered by the Secretary of State
for War to attend immediately before the
Ordnance Select Committee, and submit his
discovery to their investigation.

THE LEEDS ASSOCIATION OF

FOREMEN.

OF THE CLYDE STEAM DREDGERS.*

BY MR. ANDREW DUNCAN, OF GLASGOW. THE improvements in the channel of the river Clyde were commenced in 1770, under the direction of Mr. Goulbourne of Chester. At that time the navigable depth to Glasgow was only ft. at high water spring tides, with 13 ft. at low water; while the high water of neap tides did not reach Glasgow at all. The river was crossed by seven fords, one being as far down the river as Dumbuck, about twelve miles below Glasgow, which had only 2 ft. depth over it at low water. The first operation seems to have been the removal of the Dumbuck ford; and numerous cross jetties were afterwards shot out from either bank as far up as Glasgow, for the purpose of narrowing the channel, their outer ends being subsequently connected by parallel dykes. Soon after 1798, a few ploughs and a dredging machine worked by manual labour were employed in deepening the shallowest places; and the result of these operations was to enable vessels drawing 6 ft. of water to come up to Glasgow at high water spring tides.

A SOCIETY of managers, foremen, and drafts-3
men connected with the engineering trades of
Leeds and district has lately been formed. The
association is established for the purpose of
bringing together those engaged in the direction
and superintendence of engineering works; for
mutual acquaintance, and promoting more fre-
quent exchange of opinions on interesting ques-
tious constantly arising from the progressive
nature of the mechanical trades; and for the for-
mation of a library of standard mechanical and
scientific works. Also, for bringing under the
notice of members any subject or invention
which, from its novelty, usefulness, or otherwise,
may be instructive or interesting. Further, to
grant pecuniary assistance to such members as
may require it. This association proposes not to
discuss on any occasion the politics of the trade.
It has no secrets, but courts rather complete
publicity. Its objects are solely philanthropic
and instructive, tending to assist its members in
creditably filling the important posts confided to
them. The inaugural meeting was held on the
29th of June last, when the address was deli-
vered by the president, Mr. Thos. Harrison, of
the Steam Plough Works, in which he called
attention to the objects for which the society
had been formed, congratulated the members
upon the number of names already upon the
books, and particularly requested their attention
to the real value that might result from such an
association. It was also specially noted that the
society was totally distinct from any trades' union.
By following in its integrity the course mapped
out by its founders, this association will ulti-annually; and the minimum depth of the river is
mately prove of great benefit, not only to its imme-
diate supporters but also to collateral branches
of engineering industry.

THE ERICSSON GUN.

By the introduction of steam dredgers upon the Clyde, very important improvements have been effected in enlarging the channel of the river. In 1824 the first steam dredging machine was obtained, which now belongs to the town of Dumbarton, and is at work on the river Leven, running out from the foot of Loch Lomond into the Clyde. By that time the Liverpool traders were coming up to Glasgow at high water spring In 1831, there tides, drawing 11 ft. of water. were two vessels drawing 13 ft.; in 1836, six vessels drawing 15 ft.; in 1839, one drawing 17 ft.; in 1853, two drawing 19 ft.; in 1860, eight drawing 19 ft.; and in 1863, two vessels drawing 21 ft. arrived at Glasgow. The register tonnage of the vessels arriving and departing exceeds three millions from Glasgow now

now not less than 12 ft. at low water, with a rise of 9 ft. at average spring tides and 7 ft. at neap tides. The deepening and widening of the channel is still in progress, and more powerful machinery is in course of construction in order to hasten on the work. The depth which is now contemplated throughout the whole length of the river up to Glasgow is 15 ft. at low water, giving 24 ft. depth of high water at spring tides and 22 ft. at neap tides.

We recently noticed the discovery, by Mr. Gale, an electrician, of Plymouth, of a method whereby gunpowder may be rendered explosive or non-explosive at will. Some interesting experiments, illustrative of this discovery, were made last Saturday in a large tent at the Wimbledon rifle gathering. The process, which is very simple, consists of mixing two parts of dark impalpable powder with the gunpowder to be rendered non-explosive, thoroughly incorporating the two, and the operation is complete. The mixture at first sight differs little in appearance from the impalpable powder itself, except that on close inspection the shape of some of the grains of gunpowder can be detected. Each ANOTHER wrought-iron gun has been brought grain of gunpowder is isolated by an envelope of forward for trial in America. It is the invention of the impalpable or non-explosive powder, and as Mr. John Ericsson. This gun is of novel cona consequence, when fire is applied to the mix-struction and valuable results are expected from ture, the gunpowder will only explode grain by it by its inventor. It is of 13-inch bore, and is grain as the fire reaches it. A quick match was composed of a barrel or cone of wrought iron, thrust to the bottom of a bowl of the mixture forged in the usual manner. This barrel is thick After the match had burnt be enough to give the necessary strength in the discharge into the harbour, where the deposit direction of the axis. To resist rupture in the opposite direction, it is surrounded by broad plate iron rings of the finest wrought iron, put on in a peculiar manner by hydrostatic pressure.

and set on fire.

neath the surface a few grains of powder were exploded one by one until the match was consumed. To render the powder again explosive

all that is necessary is to place the mixture in a

fine sieve and sift away the non-explosive These rings are of course without welds, and dredging machines is kept constantly at work in

powder. The separation apparently can be
perfectly effected. No particles of the non-ex-
their fibrous character is preserved as they exist
plosive powder adhere to the gunpowder, which in the gun. According to the New York Army
burns after the operation as rapidly and with as

little residuum as before, The inventor states that in five minutes a barrel of gunpowder can be rendered non-explosive, and in another five minutes be restored to its original combustible condition. A shell might burst in a store of this mixture in bulk without any explosion except that of the shell itself. Gunpowder so treated may be stowed with perfect safety in any common shed or warehouse, and stowed also in bulk. Another reason why great care requires to be exercised in storing gunpowder is, that it absorbs moisture from the air very readily, and if not kept thoroughly dry soon becomes unfit The non-explosive powder is stated by Mr. Gale to be in this respect totally different from gunpowder; that is to say, it does not absorb moisture from the atmosphere, and, as a consequence, it protects the gunpowder with which it is mixed. The inventor burnt some gunpowder which he stated had been kept for months in the mixed form under an open shed.

for use.

Several

and Navy Gazette, this gun has undergone two
official trials, during which the charges were
gradually increased to 75 lbs. of fine powder,
and the elevation to 35 deg. The result was a
range exceeding 5 miles at this elevation, with
a solid spherical shot. Owing to the severe
strain put upon the trunnion band by the recoil
at this great elevation, it fractured.
fissures also showed themselves in the bore, a
circumstance which is quite common where the
bore is made of wrought iron. In the Horsfall
13-inch solid-forged gun, for instance, fissures
larger than these showed themselves after half a
dozen rounds; but the subsequent career of that
piece, with greatly increased charges, proved
that they did not practically affect its strength,
which is the prime condition. But this difficulty
might be surmounted by inserting a steel lining
within the gun to protect the wrought iron from
the action of the powder gases; but what is
better still, is to construct the barrel or core
wholly of steel. We should then have the ano-

As regards the deposit to be removed from the river bed, the greater portion of it comes from the drainage of the city, all the sewers of which lodges; also a considerable quantity of sand is brought down from the upper reaches of the river by the land floods, and lodges chiefly above Glasgow bridge. One of the two large double the harbour, the maintenance of which costs about £11,000 annually, and three-fourths of this entire dredging plant of the river consists of two amount may be said to be due to city sewage. The large double dredgers, and three single dredgers, making five in all; connected with which there are 350 punts, each capable of carrying 8 cubic yards or 10 tons of material; one tug steamer of 80-horse power; and four screw hopper barges; each capable of carrying 300 tons. During the last twenty years, 8,114,872 cubic yards or 10,143,590 tons of material have been removed by dredging; last year's work ending June, 1864, being 632,272 cubic yards or 790,340 tons.

The following is a general description of the two large double dredgers, Nos. 1 and 6, the latter of which is shown in the engravings, fig. 1 being a longitudinal, and fig. 2 a transverse section. The first double dredger, No. 1, was constructed in 1851 by Messrs. Murdoch Aitken and Co., of Glasgow. The hull is of iron, 98 ft. long, 31 ft. broad, and 10 ft. deep, drawing 5 ft. of water. The engine is a direct-acting marine

*Read before the Institution of Mechanical Engineers,

FIC.2

the engine through a clutch box and friction
wheel, and having a set of change wheels for the
purpose of regulating the rate of advance accord.
ing to the nature of the material that is being ex-
cavated. This rate of advance varies from about
4 ft. per minute in soft sand to 1 ft. per minute
in hard material. The dredging is done in paral-
lel cuts of about 120 ft. length. A corresponding
windlass with two mooring chains R at the stern
of the vessel gives the means of drawing back the
dredger to commence a second line of excavation
parallel to the former one; this windlass is driven
by a small high-pressure donkey engine with a
pair of 12 in. cylinders, the dredging engine and
machinery standing still during the time occupied
in going astern, which is about 15 minutes, the
speed being about 8 ft. per minute. Two side
warp lines extending from each side of the
dredger, serve to steady it constantly during the
progress of each cut, and to shift its position into
the new line of excavation; they are worked by
the surging heads T T, driven by the engine, or
by hand power when required. The kedge
anchors for these side warps are placed forwards
of the dredger; the warps are also passed round
leading blocks when required, since it is desirable
they should be as nearly at right angles to the
dredger as possible. The two warps on the side
next the sailing channel of the river are lowered
or slacked out when any vessel is passing, but are
immediately tightened up again when the vessel
has passed.

iron rollers, upon which the bucket links travel;
and a cast-iron tumbler C and H, fig. 1, at the
top and bottom ends, over which the links work.
Each ladder is suspended at the upper end by
cast-iron dead-eyes, firmly bolted to the main
framing of the dredger; through these dead-eyes
the upper tumbler shaft C passes freely, and
round them the ladder turns in being lifted or
lowered: thus the upper tumbler shaft C does
not bear any part of the weight of the ladder D.
The shaft C is of wrought iron, and works in top
and bottom brass bushes in pillow blocks bolted
to the main framing of the dredger. Each ladder
works in a vertical well K, fig. 2, passing through
the bottom of the vessel. There are 41 buckets
to each ladder; they are constructed of 5-16ths
of an inch wrought-iron plates, bent and riveted,
with a flat back, in. thick, upon which four
wrought-iron bars are riveted, having eyes at the
ends. These are connected together by two inter-
mediate links, 3 in. square, and jointed with
2 in. steeled pins, the whole forming a contin-
uous chain with 2 ft. pitch of the links. The pins
are prevented from turning in the eyes of the
bucket links which are not steeled, and the eyes
of the intermediate links are bushed with steel
on the wearing side. In another dredger, No. 7,
which is the most recent construction, the plan
is adopted of inserting a bush of hard steel 5-8ths
of an inch thick into the eyes of the single links,
while they are hot; and when worn this bush is
driven out and another inserted, so that the eyes
of the links do not wear at all. The mouth of the This dredger, No. 6, has now been at work for
bucket is made 1 in, thick at the point, tapered nine years, and has not required any repairs ex-
to in. at the sides, and is faced on the outside cepting for the wear and tear of the buckets,
with steel in. thick welded on the plate, the links, and rollers, and the usual repairs on the
mouth is shaped in a projecting scoop form, for hull, &c. The upper tumbler, however, having
excavating and lifting the material dredged, as been found too low to allow of the shoot being
each bucket in succession passes under the bot-placed at a sufficient height and slope for loading
tom tumbler H of the ladder, figs. 1 and 2.
The depth of excavation of the buckets is
regulated by the lifting chain M, fig. 1, attached
to the lower end of the bucket frame D, and
hoisted at the rate of about 26 ft. per minute by
the windlass or hoisting barrel N, which is driven
by a small shaft from the engine through a clutch
box and friction wheel, similar to those giving
motion to the buckets and also worked by a lever
upon deck. The depth of dredging is continually
gauged during work by a man stationed at the
bucket well K holding a gauging rod resting on
the river bottom, and having the lifting lever
at hand and also a brake handle for lowering the
bucket frame, so as to keep the buckets constantly
adjusted to a uniform depth of cut, according to
the surface of the ground. A self-indicating
gauge has also been fitted up on deck, so that the
captain by glancing at the position of the bucket
frame may in an instant tell at what depth below
the surface of the water the points of the buckets
are working. The greatest depth the dredger
can work at is about 28 ft.

The forward motion for the cutting of the buckets is given by the bow chain O, which is 1 in. diameter, attached to a single-fluked anchor weighing 12 cwt. placed about 600 ft. ahead of the dredger when at the commencement of a cut. The chain is hauled in with a slow motion by the windlass P, driven by a second small shaft from

the large screw hopper barges, was raised 2 ft.
higher. The steeled mouths of the buckets last
for the year's work of about nine months, when
the buckets require to be thoroughly overhauled
and put in repair. The pins and links of the
bucket chains last generally about four months,
and are replaced from time to time as required;
a supply of duplicates being kept ready on board
for the purpose. The rollers over which the
buckets travel in ascending the dredging ladder
are of cast iron, 1 in. thick in the barrel, with
wrought-iron spindles, having 1 5.8ths in. jour-
nals laid with steel, which last about three
months before being worn out; these run in
small cast-iron steps with hard wood caps, fixed
on the top flange of the ladder, which are readily
renewed when worn out, the cast-iron bush
lasting about two months, and the wood cap
about nine months. Each bucket weighs 5 cwt.,
and the total weight of each set of buckets and
links is about 7 cwt. The cubic content of
each bucket is 3 cubic feet, and the average
quantity of material brought up by each when
working in sand is about 2 cubic feet. The
number of buckets discharged per minute is 13
to 14 at the regular speed of about 6 revolutions
per minute of the tumbler shaft.

The total quantity of material raised per day
of ten working hours varies very much according
to the nature of the material dredged. Where

the dredger No. 6 is at present working, about 1 mile below the river Leven, the rate of work. ing is 150 tons per hour of the engine; while in hard ground the quantity may perhaps be only one half of this. Taking the entire work performed by this machine during last year, namely, 303,957 tons in 2,680 engine hours, the average work for a day of ten engine hours is 1,134 tons, or 113 tons per hour. The total quantity of material lifted by the two large dredging machines, Nos. 1 and 6, during the year ending 30th June, 1864, amounts to 386,752 cubic yards, of which about 250,000 cubic yards may be considered as due to maintenance, and the remainder to the permanent widening and deepening of the channel. The cost of dredging per cubic yard, taking the year ending 30th June, 1863, as per formed by No. 1 dredger, was as follows, the dredged material being conveyed away by the punts: wages, coals, stores, repairs, and 5 per cent. interest, 3.02 pence; repairs of punts, 1'59 pence; towing punts to and from place of deposit, 2.28 pence; discharging punts by waggons, 12-29 pence. Total cost of dredging per cubic yard, 19.18 pence. The cost of dredging as performed by No. 6 dredger during the same period, with the screw hopper barges for carrying away the material, was as follows:-Wages, coals, stores, repairs, and 5 per cent. interest, 4:06 pence; discharging by hopper barges, 2.30 pence; wages, coals, stores, repairs, and interest, 2.30 pence. Total cost of dredging per cubic yard, 6.36 pence. During this year No. 6 dredger was working near the two extreme ends of the river; and as during one half of the time it was attended by only two hopper barges in place of four, for discharging the material, much time was necessarily lost. This has since been rectified by the construction of additional barges.

The dredged material is disposed of according to two different modes. That filled into the 10ton punts is towed down to some convenient part of the river, and discharged by barrows or waggons on to the banks or fields adjoining. That put into the screw hopper barges, shown in the engraving, fig. 3, is carried down to Loch Long, beyond the mouth of the Clyde, and deposited by opening the hopper doors U at the bottom of the carrying space W, as shown by the dotted lines. At the place where the deposit is made, the water is upwards of 200 ft. deep, and the mouth of the loch is about 27 miles below Glasgow; the hopper barges at present at work contain each 300 tons of dredgings, and steam from eight to nine miles per hour. This latter mode is by far the most economical way of disposing of the dredged material, as seen by the above statement of the cost by the two methods; and the result has been so satisfactory that two additional barges are now being constructed, each to be capable of carrying 400 tons, making six barges in all. In conclusion it may be mentioned that a larger and more powerful single dredger is now being constructed for the Clyde Trust by Messrs. A. and J. Inglis, of Glasgow. The dimensions of this dredger will be:-Extreme length, 157 ft.; extreme breadth, 29 ft.; depth. 10 ft. 9 in.; and bucket frame capable of working in upwards of 30 ft

depth of water. The engine will be horizontal, with cylinder 44 in. diameter, and adapted for a 3 ft. stroke; the boiler will be tubular, and capable of working to 25 lbs. pressure per square inch above the atmosphere. The buckets will be 39 in number, discharging over the side; the pitch of the bucket-chain will be 30 in., and each bucket when quite full will contain 133 cubic feet. The flat bucket back with the double links will be made of malleable cast iron with the links cast solid upon it; this construction has been found to last without requiring repair for more than double the time of the ordinary backs with riveted links. The bucket rollers will not require spindles, as they will have necks cast on the ends of the rollers, which will answer for the spindles. The lower tumbler shaft will be of wrought iron having strong rings or hoops at the journals, so that when worn the hoops can be easily removed and replaced. The only other difference of any consequence from the present dredgers will be in using grooved frictional gearing for driving the hoisting barrel that lifts the dredging ladder instead of spur gearing with a friction wheel as previously described. The total cost of the dredger will be about £17,000.

the satisfaction which he would probably have experienced by a personal inspection of the premises. The Cape Cod Light is a substantial-looking building of brick, painted white, and surmounted by an iron cap. Attached to it is the dwelling of the keeper, one story high, also of brick, and built by Government. The light consisted of fifteen argand lamps, placed within smooth concave reflectors twenty-one inches in diameter, and arranged in two horizontal circles one above the other, facing every way excepting directly down the Cape. These were surrounded, at a distance of two or three feet, by large plate-glass windows, which defied the storms, with iron sashes, on which rested the iron cap. All the iron work, except the floor, was painted white, and thus the lighthouse was completed. This house consumes about eight hundred gallons in a year, which cost not far from one dollar a gallon. Let us in imagination stand with Thoreau on the luminous tower and amid the agitations of ocean, air, and ath, consider the laws by which the presiding power controls these elements. The restless sea, through all its movements, from ripple to billow, obeys the same mandate; the time of each oscillation is proportional to the square root of the length of the wave. At great depths the motion of the fluid is wholly insignificant, because at a distance below, equal to the length of a wave, the motion is only 1-535th of that at the surface. The size of the wave depends, APPLYING MOTIVE POWER TO SHIPS. therefore, upon the force of the wind and the depth of the sea. The largest on the Atlantic observed THIS invention consists in the application of a by Captain Scoresby were 550 ft. long and 30 ft. combination of steam and air as a motive high. The air, however, is not confined like the power to ships and vessels of all descriptions. sea, which has only an upward and downward It has been patented by MM. Jean Baptiste motion, except near the shore, where the force it Andreux and Engène Coulon, both of 82, contains would escape. But the whole mass of air Boulevart Sébastopol, Paris. The improve-moving as wind, has also a vibratory or wavements in the combination of steam and air motion producing sound. If the distant bell we are as follow:-A boiler of suitable size and hear is tuned to middle C of the musical scale, according to the new French standard, and the shape is used, inside which is coiled a ser temperature is at 16 deg. Centigrade, its sound is pentine copper tube or pipe, through which produced by air waves vibrating-not undulatingsteam is conducted to a second tube or pipe here- at the rate of 522 per second, each of which is about after described; the steam in passing through 215 ft. in length. The lowest octave of this note this first tube is superheated by means of boiling which could be heard would, according to Savart, water, steam, jets of gas, or other similar means. be the result of 16:31 waves per second, each For the purpose of increasing the force the about 68'8 ft. long, and the highest octave by waves superheated steam is made to escape from this moving at the rate of 33 408 per second, each '0492 first tube by a small jet into a second tube whose of a foot in length. Turning now to the light promouth is slightly funnel-shaped and whose duced by the fifteen argand lamps, we behold still The alldiameter is larger than that of the first tube; it more wonderful wave phenomena. is in passing from the first to the second tube pervading æth is, for miles around, thrown into undulations moving at an average rate of 582 that atmospheric air is introduced, the super-million of million per second, having au average heated steam drawing it into the second tube as length slightly exceeding twenty-one millionths of it enters the funnel-shaped mouth; the other an inch. These numbers, determined by repeated end of the second tube opens at the stern of the experiment, appal us, and we turn to that branch vessel. Other tubes may also lead from this of the subject where results are more palpable. second pipe to the sides of the vessel, the escape being so arranged that the steam strikes in a backward direction so as to aid in propelling the ship.

CLYDONICS.

BY PROFESSOR S. D. TILLMAN. IN a former namber we gave the first part of a paper on this subject, which was read before the Polytechnic Association of Philadelphia. At the last meeting of the Association the author, who is the President, read the following paper in conclusion of the subject:-The celebrated historian, Buckle, believed the most effective way of turning observa. tions of natural phenomena to account, would be to give more scope to the imagination and incorporate the spirit of poetry with the spirit of science. By this means our philosophers would double their resources, instead of working as now, maimed and with only one half of their nature. They fear the imagination on account of the tendency to form hasty theories. But surely all our faculties are needed in the pursuit of truth, and we cannot be justified in discrediting any part of the human mind. These views, if not applicable to methods of original research, are certainly of great moment in considering the best means of diffusing scientific knowledge; and if there is any branch of philosophy which is pre-eminently entitled to bring to its surface the free play of fancy, it is that treating of the force of waves, whether propagated through liquids, aeriform fluids, or more attenuated media. A discourse on the structure of the flame of the ordinary lamp might not gain general attention, yet how intense the interest as we speak of the particular light which a captain seeks when his vessel, freighted with human beings midst storm and darkness, has nearly reached its haven. There are scattered along our vast boundary five hundred such beacons, kept in operation at an annual expense to the United States' Government of more than a million of dollars. A description of one of these is given in the posthumous papers of the gifted Thoreau, just published under the title of " Cape Cod ;" and, although since the time of his visit a more imposing structure has arisen in the place of the old lighthouse, the account is so graphic, one feels, after its perusal,

All the phenomena attending the artificial production of light is not yet fully understood. Light is only one of the effects of the burning of hydrocarbons in the gaseous state. The solid candle and the liquid contents of the lamp must be volatilised, and brought into the same expanded state as ordinary illuminating gas before they can be burned. This condition is attained, in the case of the candle, by the heat of the flame; the liquid wax or tallow, by capillary attraction, is carried along the wick to the point where it is turned to gas. Yet light does not emanate from gases. Draper found that while gases heated to over 1,100 deg. Centigrade do not give light, all the solids subjected began to be luminous at about 510 deg. C., and they display the several colours of the prism, and finally emit white light. In the process of burning illuminating gas, the hydrogen is first combined with the oxygen of the air, and the solid particles of carbon thus deserted by the hydrogen and exposed to the heat generated by the burning gases, become incandescent and afterwards unite with oxygen forming carbonic acid gas. It is, however, true that when the carbon is consumed at the same time with the hydrogen, no light is evolved; such condition exists when the oxygen is mechanically but thoroughly mixed with the hydro-carbon gas before it arrives at the place of burning. This is effected by the Bunsen burner, in which the air is admitted at the bottom and mixed with the gas on its upward passage within the burner. The result of this simultaneous burning of both carbon and hydrogen is an increased amount of heat and an almost entire absence of light. It seems, therefore, to be essential to the production of light, that the combustion of the carbon should take place after that of the hydrogen. Steel filings dropped into a current of heated gases give forth brilliant scintillations. Hare, soon after his invention of the hydro-oxygen blow-pipe, found that a pencil of lime held before it, in the burning gases, emitted a light of intense brilliancy. Such a light, when its rays were thrown into parallel lines by means of a parabolic mirror, has been seen in diffused daylight at a distance of more than one hundred miles. But to assert that light is generated because carbon or any other solid is incandescent, is not to explain the phenomenon. Light is proved beyond a doubt, to be the result of waves moving transversely to the

line of propagation; the solid from which it proceeds must, therefore, have the power of producing such waves in the æth. The interesting question to be settled is, whether the solid itself, or the ath within it, can be set into high vibratory action by means of waves of heat having a lower rate of ve locity. Reasoning from analogy, we must decide in the affirmative.

Air waves have the power of exciting vibrations in solids which are more rapid than the waves pro ducing them. This fact was brought forcibly to my notice many years ago, when I found the low tone in which I was conversing in a certain room was constantly followed, not by an echo, but by a musical note of very high pitch: after a search the sound was found to proceed from a sheet of steel six or eight feet long by as many inches wide, standing on its end, and resting against the wall. This sympathetic action can be accounted for by the laws of harmonics. The proper tone of a bell is always accompanied by harmonic sounds readily perceptible to a fine ear. It is asserted by some musicians that every sound made by a musical in. strument is thus accompanied. The vibratory action arising from periodic pulses sometimes ap pears to be greater than the cause; this arises from the fact that a new impulse is given just before the force of the previous impulse is expended. The same remark may be applied to oscillations. In the gymnasium the self-swingers exert themselves only at the extremities of the arc. The danger of regular pulses where weight is sustained is well known. Soldiers in crossing a wooden bridge are required to break ranks and step out of tune. I have often seen the long span of a timber bridge, which was firm under the tread of a herd of cattle, thrown into quick vibration by the rapid passage of a dog across it. The condition required in this case is, thas the tread of the dog shall harmonise in time with the vibratory action due to the elasticity of the timber. Many points connected with the subject of secondary vibrations are yet to be further elucidated by experiment.

Only one other cause for æth undulations by means of carbon can now be suggested; it arises from the characteristics and conditions of the three important simple bodies which play the principal parts during ordinary combustion. Oxygen, the element of which more than one-half of our globe is composed, when isolated, is a permanent gas. No power yet applied has reduced it to the liquid state. Hydrogen, a gas sixteen times lighter than oxygen, has also no cohesive power. Natterer, of Vienna, subjected these gases separately to a pressure of 3,000 lbs. to the square inch, when at a temperature of 106 deg. Centigrade below the freezing point of water, without producing cohesion. Yet these two gases, when mixed in the proportion of two volumes of hydrogen to one of oxygen, are, by the electric spark, instantly condensed to steam, and on cooling, to water. Carbon, on the other hand, when isolated, is always a solid. No amount of heat yet applied has brought it to a gaseous, or even a liquid state. In its most condensed condition, as the diamondit had 3 55 times the specific weight of water; it is 41,890 times heavier than equal bulk of hydrogen, 2,618 times heavier than oxygen, and 2,992 times heavier than olefiant gas (CH). In the process of illumination by the combustion of hydro-carbon gases, as described, the isolation of the carbon seems to be essential. It must, therefore, instantly change its volume, and become a solid, and then as quickly assume the gaseous state, in the formation of carbonic acid gas. These rapid contractions and expansions of carbon may act as pulsations on the pervading æth, and thus generate the whole series of waves, which, commingling, form white light. It is passing strange that carbonic acid gas, a resultant in generating light and heat-including the vital heat of myriads of animals-should, after its passage from the lamp or the lung to the leaf, be again separated from oxygen by a force similar to that its constituents can generate under certain conditions.

Turning again to the Highland lighthouse, let us estimate the power expended on its lamps. The average weight of oil consumed nightly was about 16 lbs. at the time of Thoreau's visit. Taking the mean of the results of experiments by Favre, Silbermann, Dulons and Andrews, with olefiant gas (oilgas not being given), we find that 11,943 lbs. of water are raised 1 deg. C. by the combustion of 1 lb. of oil. This sum multiplied by 16, the number of, pounds used per night, and that product by 1,390 the number of foot-pounds which measures the force expended in raising 1 lb. of water 1 deg. C.that being the mechanical equivalent of heat as correctly determined by Mayer in 1842-we have 265,612,320 foot-pounds as the amount of energy expended in generating the light required for a single night. In order to fully appreciate the power of these molecular forces, it is only necessary to refer to Dr. Tindall's admirable work on "Heat as a Mode of Motion." After calculating the mechanical value of the energy developed when the atoms of 1 lb. of hydrogen and 8 lbs. of oxygen attract each other, fall, and clash together, when the

SIR,-Your notice and review of the above work in your valuable journal of the 14th inst. I have read with care and attention, the more so from having purchased the work and been greatly disappointed in it; and also at finding, instead of being a scientific work got up in a proper manner, and in a way commensurate with the reputation as a scientific writer hitherto maintained by Mr. Bourne, that it is nothing more than a cook-up" of the dif ferent price-lists and illustrated catalogues of those makers who have favoured Mr. Bourne with the use of their engraved blocks, and in which also many recent improvements," or at least some equally as recent as many of the examples given, are entirely omitted!

For instance, we find very liberal use made of the illustrated price-list and catalogue engravings of Messrs. Carrett and Marshall's donkey pumps and other contrivances, whilst the only other donkey noticed is that of Messrs. Hawthorn; then we find a centrifugal pump, and one of the least efficient it may be remarked, well described and puffed, whilst all other pumps of this description, one of which at least is far superior to the example quoted, are entirely omitted and unnoticed. Then we have. a Harvey, honorary secretary to the "Buckle Medescription and engraving of a double cylinder ex-morial," enclosing a list of subscriptions received pansion engine, which is notoriously one of the least efficient of this kind of engine. Next, we have the steam cranes and winches of one maker