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seem to run on to a great length. The milky-way is undoubtedly nothing but a stratum of fixed stars. It is very probable that this great stratum is that in which our sun is placed, though not in the centre of its thickness, and we seem to be so situated as to view it sideways, and hence its brilliancy. The sun is therefore in this great stratum, and probably not far from the place where some smaller stratum branches out from it. The milky-way is the appearance of the projection of the stars in this stratum, and its secondary branches. By applying ourselves with all our powers to the improvement of telescopes, which I consider as yet in their infant state, we shall in time perhaps be able to delineate the interior construction of the heavens."

"The stupendous sidereal system which we inhabit, this extensive stratum, and its secondary branch, consisting of many millions of stars, is in all probability a detached nebula. In the most crowded parts, I have had fields of view that contained no less than 588 stars, and these have continued for many minutes, so that in a quarter of an hour no less than 116,000 stars passed through the view of my telescope."

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My present telescope will not only reach the stars at 497 times the distance of Sirius, so as to distinguish them, but has also the power of showing the united lustre of the accumulated stars that compose a milky nebulosity at a distance far greater. There are many round nebula of about five or six minutes in diameter, the stars of which I can very distinctly see, the centres of which may be 600 times the distance of Sirius from us, and, from other considerations, perhaps, 6000 times. A nebula which by my telescope is perfectly milky cannot well be supposed to be at less than 6000 or 8000 times the distance of Sirius."

New Experiments on Heat. By Col. Sir B. THOMPSON, Knt. F.R.S.[1786.]

EXAMINING the conducting power of air, and of various other fluid and solid bodies, with regard to heat, I was led to examine the conducting power of the Torricellian vacuum. From the striking analogy between the electric fluid and heat, respecting their conductors and non-conductors, (having found that bodies in general, which are conductors of the electric fluid, are likewise good conductors of heat, and, on the contrary, that electric bodies, or such as are bad conductors of the electric fluid, are likewise bad conductors of heat,) I was led to imagine that the Torricellian vacuum, which is known

to afford so ready a passage to the electric fluid, would also have afforded a ready passage to heat. The common experiments of heating and cooling bodies under the receiver of an air-pump I concluded inadequate to determining this question; not only on account of the impossibility of making a perfect void of air by means of the pump; but also on account of the moist vapour which, exhaling from the wet ́leather and the oil used in the machine, expands under the receiver, and fills it with a watery fluid, which, though extremely rare, is yet capable of conducting a great deal of heat: I had recourse, therefore, to other contrivances.

It appears that the Torricellian vacuum, which affords so ready a passage to the electric fluid, so far from being a good conductor of heat, is a much worse one than common air, which of itself is reckoned among the worst: for, when the bulb of the thermometer was surrounded with air, and the instrument was plunged into boiling water, the mercury rose from 18° to 27° in 45 seconds; but in the former experiment, when it was surrounded by a Torricellian vacuum, it required to remain in the boiling water one minute 30 seconds = 90 seconds, to acquire that degree of heat. In the vacuum it required five minutes to rise to 48°; but in air it rose to that height in two minutes 40 seconds; and the proportion of the times in the other observations was nearly the same.

It appears from other experiments, that the conducting power of air to that of the Torricellian vacuum, under the circumstances described, is as 1000 to 702 nearly; for the quantities of heat communicated being equal, the intensity of the communication is as the times inversely.

By others it appears, that the conducting power of air is to that of the Torricellian vacuum as 913 to 1618 inversely, or as 1000 to 603.

Taking now the conducting powers of mercury=1000, the conducting powers of the other mediums, as determined by these experiments, will be as annexed, viz.

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And in these proportions are the quantities of heat which these different mediums are capable of transmitting in any

given time; and, consequently, these numbers express the relative sensible temperatures of the mediums, as well as their conducting powers.

On the Strata observed in sinking for Water at Boston, Lincolnshire. By Mr. JAMES LIMBIRD, Surveyor to the Corporation.[1787.]

MAY 7. 1783, George Naylor, of Louth, well-borer, began. to bore at the well in the Market-Place, Boston; which had been sunk and bored to the depth of 186 feet from the surface, in 1747, by Thomas Partridge. The well was made about six feet in diameter at the top, five feet at the bottom, and 27 feet deep, and the earth prevented from falling in by a circular frame of wood, which goes from the surface of the earth to the depth of 21 feet six inches, and is there supported by brick-work, laid on a bed of light coloured blue clay, which continues to the depth of 36 feet from the surface, where is a bed of sand and gravel about 18 inches thick, and under it the same sort of blue clay as before, which continues to the depth of 48 feet from the surface. Below this

is a bed of dark-coloured stone, like rag-stone, about six inches thick, from under which George Naylor says that a salt spring issues. Beneath this layer of stone is a bed of darkblue clay, which continues to the depth of 75 feet from the surface, where is a bed of stone, of a lightish colour, about six inches thick, and under it a bed of dark-blue clay, which continues to the depth of 114 feet from the surface, where is a bed of stone, of a brightish colour, about eight inches thick, and under it a bed of gravel, about six inches thick, where George Naylor says there is another salt spring. Under the gravel is a bed of dark-coloured clay resembling black-lead, which continues to the depth of 174 feet from the surface, when it changes to a chalky clay, intermixed with small pebbles and flints, which continues about three inches, and then changes to the same kind of dark-coloured clay as before; in which, after boring to the depth of 186 feet from the surface, he came to the solid earth bored to, in 1747, by the abovementioned Thomas Partridge. After boring in the same kind of clay to the depth of 210 feet from the surface, it changes to a lighter-coloured one, which continues about six inches, and then changes dark again, and continues so to the depth of 342 feet from the surface, where is a bed of shells and white-coloured earth, about half an inch thick, and under it a

light-coloured earth like that at 210 feet from the surface, and under it a bed of dark-coloured clay.

At the distance of 447 feet from the surface there is a bed of dark-coloured earth, mixed with chalk and gravel, which continues to the depth of 449 feet 10 inches from the surface, where is a bed of dark-coloured earth without any chalk and with very little gravel, which continues to the depth of 454 feet seven inches from the surface; there it changes to a dark-coloured earth, mixed with chalk and gravel, which continues to the depth of 456 feet eight inches from the surface, and then changes to a dark-coloured earth without any chalk, and with very little gravel, which continues to the depth of 457 feet from the surface, and then changes to a lighter colour; and this continues to the depth of 462 feet and four inches from the surface, where it changes to a darker colour, and so continues to the depth of 470 feet three inches from the surface. Here the ground changes to a darkcoloured earth, mixed with chalk and gravel, which continues to the depth of 470 feet seven inches from the surface, where he came to a bed of stone, like rag-stone, about 13 inches thick, which ground into powder with the wimble, and mixed with the earth. Under this bed of stone is a dark-coloured earth, without any chalk, and with but little gravel, which: continues to the depth of 472 feet from the surface, when it changes something lighter, and continues so about two inches, where the earth appears to be mixed with chalk and gravel, and continues so for about one inch, when it changes to a black silt, having a great deal of light-coloured sand in it.

Of Three Volcanoes in the Moon. By W. HERSCHEL, LL.D. F.R.S. — [1787.]

APRIL 19. 1787, I perceive three volcanoes in different places of the dark part of the new moon. Two of them are

either already nearly extinct, or otherwise in a state of approaching eruption; which, perhaps, may be decided next lunation. The third shows an actual eruption of fire, or luminous matter.

April 20. 1787, the volcano burns with greater violence than last night. I believe its diameter cannot be less than 3", by comparing it with that of the Georgian planet; as Jupiter was near at hand, I turned the telescope to his third satellite, and estimated the diameter of the burning part of the volcano to be equal to at least twice that of the satellite. Hence we may compute that the shining or burning matter

must be above three miles in diameter. It is of an irregular round figure, and very sharply defined on the edges. The other two volcanoes are much farther towards the centre of the moon, and resemble large, pretty faint nebulæ, that are gradually much brighter in the middle; but no well defined luminous spot can be discerned in them. These three spots are plainly to be distinguished from the rest of the marks on the moon; for the reflection of the sun's rays from the earth is, in its present situation, sufficiently bright, with a tenfeet reflector, to show the moon's spots, even the darkest of them: nor did I perceive any similar phenomena last lunation, though I then viewed the same places with the same instrument.

The appearance of what I have called the actual fire or eruption of a volcano exactly resembled a small piece of burning charcoal, when it is covered by a very thin coat of white ashes, which frequently adhere to it when it has been some time ignited; and it had degree of brightness, about as strong as that with which such a coal would be seen to glow in faint daylight. All the adjacent parts of the volcanic mountain seemed to be faintly illuminated by the eruption, and were gradually more obscure as they lay ac a greater distance from the crater.

Experiments made to determine the positive and relative Quantities of Moisture absorbed from the Atmosphere by various Substances, under similar Circumstances. By Sir BENJ THOMPSON, Knt. F. R. S.-[1787.]

HAVING provided a quantity of each of the under-mentioned substances, in a state of perfect cleanness and purity, says Sir B. T., I exposed them, spread out on clean China plates, 24 hours in the dry air of a very warm room, the last six hours the heat being kept up to 85° of Fahrenheit's thermometer; after which I entered the room with a very accurate balance, and weighed equal quantities of them, as expressed in the following table. Then each substance being equally spread out on a clean China plate, they were removed into a very large uninhabited room on the second floor, where they were ex posed 48 hours, on a table placed in the middle of the room, the air of the room being at the temperature of 45° F.; after which they were carefully weighed in the room, and were found to weigh as under mentioned.

They were then removed into a very damp cellar, and placed on a table, in the middle of a vault, where the air,

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