LITERARY AND SCIENTIFIC. 65 



Having thus introduced the elementary bodies, Mr. W. proceeded to direct the 

 attentionof his audience to the laws which regulate their union with each other. 



The matter of which the elementary bodies are composed is conceived by most 

 philosophers of the present day to consist of exceedingly small particles or atoms, 

 difTering in weight from each other, but incapable of division — hence they must be 

 considered as hard and penetrable. Some philosophers have indeed argued, and 

 with great plausibility, that matter is capable of indefinite division. It is certain 

 we can have no idea of a particle of matter th«,t has been divided, whose half may 

 not again be divided, and so on, ad infinitum. But here is one of the barriers to 

 human knowledge — here we are compelled to confess our ignorance of the original 

 formation of matter. In reasoning, however, upon various chemical phenomena, 

 and observing the constant, the uniform, and definite proportions of the elements, 

 and the unchangeable nature of these elements, it is found, if not more reasonable, 

 at least more convenient, to consider them as atoms or particles, hard, impenetrable, 

 and incapable of further division. But these atoms of themselves would be totally 

 inert, and exhibit no disposition to combine, were it not for certain properties with 

 which they are indued, or for certain subtle agents which govern their action upon 

 each other. These agents, or properties of matter, are, attraction of gravitation^ 

 heat, light, and electricity. They are sometimes called imponderable agents, 

 because they do not appear to possess weight ; and subtle, because they cannot be 

 confined in any way, or obtained in an uncombined state. Although it is usual to 

 consider the phenomena of attraction, of gravitation, heat, light, and electricity 

 separately, and as resulting from distinct causes, yet it is not improbable that some 

 of them are modifications of each other, and may be considered as belonging to 

 the same family, as the offspring of one common parent. 



Attraction of gravitation is that power which causes a stone or any other 

 substance, when thrown into the atmosphere, to fall back to the earth. It acts 

 upon all bodies in proportion to their density — its influence is universal — it ex- 

 tends to the planets, and tends to preserve them in their respective orbits. 



If a ball be discharged from a piece of artillery, it will describe a curve, and at 

 length fall to the ground — the impulse given to the ball endeavours to drive it 

 in a right line, but the attraction of the earth gradually draws it towards 

 itself. These two forces are termed the centripetal and centrifugal forces. If 

 the impulse given to the ball were exerted to a certain extent in free space, having 

 no atmosphere to resist its motion, it would continuously revolve round the earth, 

 as the planets do round the sun, in consequence of the equilibrium of these two 

 forces. 



At the surface of the earth gravitation is most powerful. It decreases as we 

 approach the centre of the earth, as the distance from the surface increases — but 

 it decreases as we recede from the earth, as the square of the distance — hence 

 bodies in falling acquire an increase of velocity. These laws were first clearly 

 demonstrated by Sir Isaac Newton, and by them he explained the motions of the 

 planets and the various systems of the universe. 



When bodies are brought very near to each other, so as to appear in actual 

 contact, they attract each other still more powerfully by a force which is probably 

 only a modification of gravitation, but which is usually termed attraction of cohesion, 

 or aggregation. Two flat pieces of glass or lead, when brought together, adhere 

 firmly, in consequence of attraction of cohesion. Water in a glass vessel assumes 

 a concave surface, mercury a convex surface; the former being attracted by the 

 sides of the glass, while the latter has more attraction for its own particles than 

 for the glass. By this power, metals, stones, wood, and all the most solid ma- 

 terials of the globe preserve their respective forms. The dew that falls upon the 

 leaves of many vegetables, particularly upon the cabbage-leaf, forms itself into 

 beautiful spheroidal drops, and as a poet has expressed himself of the tear that 

 flows down the cheek — 



" That very law which moulds a tear, 

 And bids it trickle from its source. 

 That law preserves the earth a sphere, 

 And guides the planets in their course." 



Mr. W. here exhibited several experiments in illustration of attraction of 

 cohesion, and then proceeded to the consideration of heat. There appears, he 

 February, — vol. ii. no. vii. k 



