How do you imagine that the same force which operates upon the ultimate particles of bodies, so as to produce composition and decomposition, can be sufficient to preserve the planets in their orbits?*

"We can neither comprehend the one nor the other; nor can we see why the Almighty might not as easily bestow upon one species of matter the power of acting upon another when at a distance, as the power of being acted upon

* A passage of bishop Watson's will perhaps furnish as good a reply to this question as can be given. "We feel," says he, "the interference of the Deity every where, but we cannot apprehend the nature of his agency any where. A blade of grass cannot spring up, a drop of rain cannot fall, a ray of light cannot be emitted from the sun, nor a particle of salt be united, with a never-failing symmetry, to its fellow, without him; every secondary cause we discover, is but a new proof of the necessity we are under of ultimately recurring to him as the one primary cause of every thing."

Dr. Herschel has shown, that not only the planets in our system are preserved in their orbits by mutual attraction, but that in the sideral systems the double stars are so situated with respect to each other, that they must be subjected to mutual gravitation, and that they can only preserve their relative distances by a periodical revolution round a common centre. What he calls the insulated stars he imagines to be nearly out of the reach of mutual gravitation. He considers our sun and all the brightest stars to be of this class. They are at such immense distances, that he calculates that Sirius (the nearest of the fixed stars to us) and the Sun, if the power by which they are preserved in their orbits were withdrawn, would be 33 millions of years in falling together. The same philosopher has said, that though light travels at the astonishing velocity of 200,000 miles in a second, some of the nebule are so far from us, that the rays of light must have been nearly two millions of years in passing from them to our system. According to a writer in the thirty-second volume of the Monthly Review, N. S. 523, astronomers are now acquainted with no less than 2120 of these nebulous stars. Probably they are so many distinct worlds, appropriated by the Author of Nature for the re

and changed by matter when in actual contact."*

Is the consideration of this universal property of matter calculated to produce any peculiar reflec

tions?

The contemplation of this subject has a natural tendency to promote the most profound feelings of awe and admiration; for the understanding of the highest intelligences sinks into nothing, when compared with the energy of that Omnipotent Being, who had wisdom to contrive, and ability to endue the matter which he had formed with the astonishing power of operating upon its fellow matter, either in contact, or when separated by the infinity of space. Well might a writer of antiquity assert, that " God saw every thing that he had made, and behold it was very good."+

ception of intelligent beings, and for the abodes of rectitude and felicity;

"Lightnings and storms His mighty word obey,

And planets roll where He has mark'd their way."

Having now completed my original design, of furnishing the YOUNG with an elementary treatise on chemistry, it may be necessary to apologize to some readers for the introduction of those moral reflections which so frequently occur. This cannot be done better than in the language of a late popular writer:-"Every man," says he, " has a particular train of thought into which his mind falls, when at leisure, from the impressions and ideas that occasionally excite it; and if one train of thinking be more desirable than another, it is surely that which regards the phenomena of nature with a constant reference to a supreme intelligent Author."-PALEY.

* Thomson's Chemistry, second edition, vol. iii. 176.

ADDITIONAL NOTES.

1.

Of Specific Gravity.

THE common method of taking the specific gravity of the metals, or of any solid body, is by comparing the difference which there is in their weight when weighed in air and in water; that is, to divide the absolute weight by the loss, and the quotient is the specific gravity. Thus, if a mineral, which weighs three ounces in air, weighs only two ounces when weighed in water, the specific gravity of such mineral is 3; that is, if water, as it generally is, be called 1.000, the substance now examined is 3.000; or, to make it plain to the young student, if a pint of water weigh one pound, the same bulk of the mineral will weigh three pounds. See page 35.

A more ready way to determine the specific gravity of solids is to fill a phial with water, and note the weight of the whole accurately in grains. Then weigh 100 grains of the mineral or other substance to be examined, and drop it gradually into the phial of water. The difference of weight of the bottle with its contents now, and when it was filled with water only, will give the specific gravity of the matter under examination. For example, if the bottle weighs 50 grains more than it did when it was filled with water only, it shows that 100 grains of the mineral displace only 50 grains of water, and consequently that it is twice the specific gravity of water. This method is said to have been discovered by Archimedes. See Note *, page 32.

The specific gravity of fluids is generally determined by an areometer, which is a graduated glass tube with a bulb, so contrived that it may swim in the fluid in a perpendicular position. The specific gravity is shown by the degree to which this instrument sinks in the fluid to be examined, and this will consequently always be lower in proportion as the liquid is lighter.

The specific gravity of ardent spirits is generally ascertained by means of a hydrometer, of which various kinds are sold by the mathematical-instrument-makers.

The following method, which was contrived by Dr. Lewis, the celebrated author of the Commercium Philosophico-Technicum, was communicated to me by the amiable Samuel Moore, esq. late secretary to the Society for the promotion of arts, manufactures, and commerce.

In this method the specific gravity of a liquor is estimated from the excess of the weight of a certain measure of it above that of an equal measure of distilled water. A set of weights is made for this purpose, called carals, or cadukes, in the following

manner:

A convenient bottle being procured, the tare of the bottle is first taken; it is then completely filled with distilled water; the weight of the water is accurately divided into two equal parts, and a weight made equal to one of these parts is marked 64; by continuing the division, are obtained the weights 32, 16, 8, 4, 2, 1, carats; so that a carat is the 128th part of the weight of the water. Another weight is then made which counterpoises the bottle when filled with water; and so many carats as the bottle filled with an alkaline ley, or any other liquor, weighs more than this waterpoise, so many carats strong is the liquor said to be.

In taking the specific gravity of bodies, an attention should always be paid to their temperature, as the specific gravity of a body, when expanded by caloric, will always be less than it is when at a low temperature.

II.

Of a curious Property of Charcoal.

A property of which charcoal is very eminently possessed, and which may be regarded as a singular one, is that of absorbing, even when cold, aëriform fluids, and condensing them in its pores, in quantity exceeding many times its own bulk. A very interesting application may be made of this property. The gases which are absorbed suffering so great a condensation, two gases introduced at once into the pores of the charcoal may perhaps be made to combine. It appears from the 32d vol. of the Annales de Chimie, that water has actually been formed by this means. The subject deserves to be prosecuted; and if strong mechanical pressure were applied at the same time, it is probable such combinations might be diversified, and carried to a greater extent. More on this subject may be seen in Murray's Chemistry, 2d edition, vol. ii. page 486; and in the Journal de Physique for 1788.

III.

Of Ebullition.

Under an exhausted receiver, water will boil at the heat of 92° of Fahrenheit's thermometer; whereas, under the usual pressure of the atmosphere, it does not boil till it is heated to 212°; though, as the atmosphere varies in density, it occasions some little variation in this respect; for Sir George Shuckburgh found by experiment, that when the barometer was at 26 inches, water boiled at less than 205 degrees, but when it was at 31 inches it required to be heated to near 214° before it would boil.

Under the common pressure of the atmosphere

Dr. Black made experiments upon several liquids in vacuo, and found that in general they all boiled with about 140 degrees of heat less than when bearing the weight of the atmosphere. Vitriolic ether (if the pressure of the atmosphere be removed) will boil when 52 degrees below the cold sufficient for freezing water. See pages 49 and 97.

IV.

Of the Combinations of Caloric.

When water is in the state of ice, it combines with caloric, without discovering by the thermometer any rise of temperature; but the moment the whole becomes fluid, every addition of caloric expands the mercury in the thermometer till the water arrives at 212", when on a sudden the thermometer ceases to rise, though the water continues to receive and combine with a vast quantity of caloric. On these curious facts Mr. Murray has remarked, "We see no cause why, for a great extent of the thermometrical scale, bodies should receive caloric without entering with it into any intimate combination; why, when the temperature is raised to a certain point in each body, this combination should suddenly take place; and why, after another interval in the thermometrical scale, it should be renewed;-for example, why water at 82°, and, under the