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Required, the elevation and plan being given, to delineate a Steam Engine in Practical Perspective.

The pump rods and minutiae of the engine are omitted, as being an unnecessary addition to a design, already of so complicated a description.

To explain this figure, it will be merely necessary to distinguish the rays and lines of elevation of the different parts, viz.

To the boiler belong the rays 4, 6, 9, 12, and the line of elevation, G, H, 5.

To the cistern belong the rays 1, 2, 5, and G H, 1.

To the cylinder belong the rays 8, 10, 11, and G H, 3 and 4.

To the beam standard, a, belong the rays 5, 9, 7, and G H 2.

To the fly wheel belong the rays 2, 3, 5, 6, and G H, 1; and the beam is found by the rays 13 and 14, its elevation being ascertained by the height of the standard.

The size of the drawing precludes the possibility of referring more minutely to the various lines, but if the previous rules are well understood, the student will have no difficulty in comprehending this problem.

The apparent disproportion between the size of the cylinder in the elevation and picture, is illustrative of the observations in my last, but my readers must take into their consideration, the difference in the points of view.

Conclusion.

In bringing these essays to a termination, I have endeavoured, and I hope successfully, to fulfil my origi

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nal design (see introduction); and though these papers have been more particularly devoted to mechanical purposes, they are no less applicable to general use.

In so limited a space, general rules are all I could lay down, and if I am censured for omitting further examples of machinery, let it be ob served, that in an octavo page, drawings of a complicated piece of mill work, would be of such dimensions, as to render the visual rays too minute for explanation, nevertheless, a draughtsman, perfectly master of the preceding pages, would find little difficulty in making any drawings.

Great accuracy and attention are requisite to a beginner, who would be, no doubt, a little incommoded by the multiplicity of lines and in the choice of his stations, &c. but prac tice would soon make him master of all these points, and he should remember, no science, however simple, can be acquired without some application; and should the expert mathematician exclaim against the omission of many of Brook Taylor's and Nicholson's Theorems, let him consider that these papers are intended chiedy for the use of those ignorant of the theoretical principles of the science; and that it has been my aim throughout, to throw as few obstacles as possible in the way of the aspiring stu dent, and that by these rules, though the humble mechanic may not be able to produce a delicately finished drawing of inventions, which, for want of such a medium, might otherwise be lost to the world, he may yet exhibit a correct and intelligible representation.

The numerous errors, typographical and pictorial, which, (notwithstanding the unremitting attention and disregard to expense, manifested on all occasions. in the conduct of this Magazine, by its Editor,) must, unavoidably, creep into papers incapable of receiving the corrections of their authors; and the many defects in their arrangement, inseparable from this mode of publication, must be excused, by my readers, on these grounds. But should this little work ever come before the public in a separate form, it may doubtless, in these respects, be materially improved.

And now, with sincere thanks to those gentlemen who have afforded me their advice and assistance during the progress of these essays, and gratefully acknowledging the favourable manner in which they have been received,

I remain, Sir,
Your obedient Servant, and
Well wisher,

M. H.
London Institution, Dec. 1, 1826."

GRATUITOUS LECTURING.

Sir,-When "Aurum" and "Argens" are in the field, struggling so manfully for the keys of knowledge, it would ill become so ancient a friend and servitor of theirs as the undersigned, to remain an idle spectator. Many is the time they have stood for him, when, by reason of his weight, he was himself unable to move about; and the least he can do in return is, to give them a lift on an occasion like this. He may take leave also to say for himself, that though his face is rather of the brazen cast, the brains within have a very considerable reputation for acuteness; so much so that, when at times the generosity and profusion of "Aurum" and "Argens" have procured for them the appellation of pounds foolish, it is the penny wisdom of your humble servant which has been almost always the means of bring them round again.

The present contest indeed may be considered as already next to decided; for "T. M. B." who first took the field

in defence of Gratuitous Lecturing, (Saturday, Nov. 4,) has since quietly

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abandoned it; and his auxiliary, “Viator," after getting soundly thrashed by him of the golden casque, and stripped of nearly every feather that covered his nakedness, has taken flight to the church steeple, and thence croaks out to all the passers bye, that " Jackdaw" Aurum (he call names, Oh, not for the world!) is beneath his notice, and "may now do as he pleases." Ah! Mr. Argens, how could you confound such an ill behaved bird as this "Viator" with our old and right trusty friend T M. B. Could all the flapping and screaming of the creature blind you to the mighty difference between them? The one so

pluckless and petulant, and the other all manliness and sincerity.-To mistake a Tom-tit for an Eagle, or a Gosling for a Swan, were a trifling blunder compared to this.

I am inclined, Sir, to think, that Gene ralissimo Aurum has committed an error

in saying that the attendance on the Lectures of the London Mechanics' Institution has recently been on the decline. It is but charitable, however, to suppose that he gave us his own impression of the fact, rather than that he wilfully misrepresented it. No one indeed can imagine he would be so foolish as to make an intentional misstatement of a fact which so many hundreds could instantly contradict. But, admitting that he is in the wrong as regards this single and merely subordinate circumstance, it is surely arguing after a new fashion to set him down as being therefore in every thing else unworthy of regard. To assume such airs as "Viator" has done, on account of a slip of the tongue like this, is but a braggart's way of covering a defeat on every other point. It puts one in mind of the fencer who, pushed into a corner, and, gasping for breath, suddenly put up his sword, and claimed all the honours of a triumph because his antagonist happened, in the crisis, to drop his sword-knot.

To be done however with this recreant-for I presume it is with every one's leave, and nobody's regret that he quits the field-allow me to remind your readers that not one of all the argu ments so powerfully urged by "Aurum" and "Argens" against Gratuitous Lecturing, has as yet been met by any thing like a fair and to-the-point answer. It stands still without contradiction, that to solicit and accept of in

struction in the arts and sciences, from

your better informed neighbour for nothing, in order that you may make

something of that instruction in the way of pounds, shillings, and pence, is in reality as mean and beggarly, as to solicit and accept of food and clothing or nothing, in order that you may be spared the wholesome necessity of earning them by your own industry. No one, at least, has offered to shew that there is the slightest difference between the two cases. It is still also as true as ever, that what "lightly comes, lightly goes." It is still, too, unquestioned and unquestionable, that what you beg you cannot order, and that you must, therefore, take gifts as they happen to be showered upon you-the mustard perchance before the beef, or the beef without the mustard. And it is still (to hasten to the end of the catalogue,) an undisputed fact, that all the most zealous and intelligent friends of the working classes, Mr. Brougham and Dr. Birkbeck in particular, concur in these views of the subject. Believe me to be Sir,

Your's as well as

"Aurum" and "Argens's"

Most devoted servant, THE COPPER CAPTAIN.

P. S. I have said nothing of the words of David Honor, for certes he is not of

the race of Solomon. R. W. D. is of a better class of reasoners, but every person must see that he loses sight of general principles in individual example. It is a maxim as old as the hills, that exceptions prove nothing.

STRENGTH AND QUALITY OF HOPS.

Sir, I shall feel obliged if any of your correspondents can inform me, In a future number of your truly valuable publication, the best method of ascertaining the strength and quality of hops. I am a private brewer, and generally observe the old rule of a pound of hops to a bushel of malt. I usually judge of them by appearance, and rubbing them between the hands, &c. I, notwithstanding, sometimes find, with the same quantity of hops, a great variation in the bitterness of my beer.

If any

of your very numerous readers can assist me in the difficulty, they will confer an obligation on your constant reader,

AMICUS SCIENTIÆ,

1.

Sir,In your magazine for Ja nuary last, No. 118, p. 87, there is a table for the construction of sun dials, by Mr. Smith, (from the Phi losophical Magazine.) I should be extremely obliged to Mr. M. Smith, or any other correspondent, who would be kind enough, to favour me with the method by which it was constructed, through the medium of your magazine.

I am, &c.

C. K.

1

GEOGRAPHICAL EXERCISE.

Whether does an inhabitant of the equator move through a greater or less portion of space in the night than in the day? And what are the greatest and least velocities? Shew likewise, how much greater a portion of the earth's annual orbit does a person move through from six o'clock in the evening, until six o'clock in the morning, than another inhabitant does, from six o'clock in the morning, until six o'clock in the evening? A solution from some of your numerous and ingenious correspondents, is respectfully requested by,

A Member of the Literary and Philosophical Society of Armley, near Leeds.

FALLING BODIES.

The American newspapers men tion a case which has lately puzzled the wise of that country considerably. Two balls, of the same shape and density, the one weighing six pounds and the other an ounce, being dropped simultaneously from the belfry of a meeting-house, the little ball went ahead of the big one for some time, and betting was three to one in its favour-when lo! all of a sudden, the big ball suddenly shot ahead of the little one, and came to the ground first! Will some of our

1

* Professor Millington proposes that the dials of church clocks, instead of being illuminated externally by y gas or other lights, should be made transparent. The following remarks by the professor on the subject we extract from a letter in the Atlas.

I foresee many difficulties in the external illumination of church clocks, from their height and the danger that would in some cases attend the lighting of the necessary lamps, as well as the difficulty of fixing them; besides which, they would not only be unsightly, but even in the way during the day time, and in tesmpestuous weather it would be difficult to keep them alight, (even though inclosed in lanterns,) on account of their elevated and exposed situations. Now, by making the dials of leaded or casement ground glass, with the figures so gilt or painted as to be opaque, a single and internal light would answer every purpose, at the same time that it would be easily managed, and would be perfectly protected. It would also be more economical, both in the first expense and afterwards, because a much less quantity of light would answer the purpose, and I am sure

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the effect might be rendered beautiful by the display of a little taste. St. Paul's Cathedral offers an excellent opportunity of trying the experiment, because there the central part of the dial is already formed of glass, upon which a night dial might be painted, while the figures of the day dial would remain without any alteration in the present stone framing."

PRESERVING POTATOES.

Sir,-Having spent a very considerable portion of my life on salt water, (more than twenty-four years,) I must naturally be supposed, during such a period to have felt and experienced many of its usual attendant privations. Trifling as it may seem to a landsman, one of those serious privations (to me, at least,) was the want of a good potatoe. None, perhaps, but those who have been pent up for nine or twelve months or more, engaged in blockading enemies' ports, and similar services, can well imagine how grateful a supply of this valuable root is to those so situated. Melancholy, indeed, is the sound, when the wardroom steward announces to the caterers that the last of the murphies" is about to be used. I have long considered that some mode might be adopted to make this esculent of more use to voyagers. To do so completely, germination must be prevented, and the natural juices must be kept preserved, if possible, in their fresh state, for on that I imagine will depend their antiscorbutic qualities. I was induced to try imbedding potatoes in different substances, and confining them in jars for a twelvemonth, but did not succeed as to stopping the germination. One experiment seems to offer a mode (on a small scale at least,) for getting a supply at sea, which, however small, to a sick person living for a long period on salt diet, might eventually be the means of preserving life. In March. I found, on digging in the garden, a potatoe, (the oakapple, a large sort,) which had lain