66 LITERARY AND SCIFNTIFIC. 



observed, to be another power in nature upon which the various forms of matter 

 greatly depend. It is that power which occasions in us the sensation of heat, and 

 is now called caloric. 



While attraction of cohesion is always endeavouring to bring the particles of 

 matter nearer to each other, caloric is endeavouring to separate them to a greater 

 distance — hence result the various forms of solid, liquid, and gaseous bodies. 

 When attraction of cohesion predominates, the substance acted upon is solid, — 

 when cohesion and calorific repulsioli balance each other, the substance assumes a 

 liquid state, — when calorific repulsion prevails, the substance becomes aeriform or 

 gaseous. This is exemplified in the several states of ice, water, and steam. 



Suppose the power of cohesion were suddenly withdrawn from the earth, leaving 

 its antagonist, caloric, to exert its power uninfluenced, what would be the effect ? 

 The particles of matter of every kind, even of the hardest rocks, would separate 

 from each other and be driven into the immensity of space, leaving no appearance 

 of anything material. How easily by such an act might the Almighty destroy a 

 world. 



Mr. W. illustrated the nature of cohesion by a variety of experiments. 



The next agent, observed Mr. W., is light— -ihe influence of which upon the 

 animal and vegetable kingdoms is particularly manifest. The infinite variety of 

 colours in the vegetable kingdom, the delightful odours of flowers, and their 

 delicious fruits, depend entirely upon the genial influence of the light and warmth 

 of the sun. But even unorganized matter is in some degree under the influence 

 of light, and many chemical phenomena are produced by its presence. The com- 

 bination of chlorine and hydrogen gases, which constitute muriatic acid, does not 

 take place without the presence of light. The crystallization of bodies is greatly 

 influenced by light. Steel needles are rendered magnetic by the violet-coloured 

 ray of light. 



The last agent which it will be necessary to notice is electricity. The influence 

 of this agent in the economy of nature is exceedingly important, and in many cases 

 most surprising. Among the natural phenomena dependent upon electricity, we 

 may enumerate the formation of clouds, of dew, rain, hail, and snow, and probably 

 the aurora borealis. The vital principle of animals and of vegetables is considered 

 by some physiologists as dependent upon electricity. The simplest mode of 

 exciting the electricity of bodies is by friction, as was done in amber by the 

 ancients. But it may also be made sensible to us by other means. By heating 

 some crystalline bodies, as the tourmalin and boracite, they exhibit electrical 

 phenomena ; by the mere contact of two dissimilar metals, as was first shewn by 

 Volta, and hence it has been called Voltaic electricity ; and also by the mixture of 

 bodies chemically. It is very probable, indeed, that what is called chemical attrac- 

 tion or affinity, is entirely dependent upon the electrical relations of bodies. 



It has also been rendered highly probable by recent discoveries that magnetism 

 is identical with electricity. Magnetic attraction may easily be communicated to 

 a bar of iron by the influence of electricity. So extraordinary, indeed, is this 

 influence, that a bar of iron about two feet long may be instantly rendered so 

 powerfully magnetic as to support a weight of two or three hundred pounds, and 

 by a combination of such bars a weight of more than two thousand pounds has 

 been supported. 



Mr. W. exhibited this experiment by a very simple but powerful apparatus. 

 He then said, having briefly noticed the influence which attraction of gravitation, 

 heat, light, and electricity, have in the various operations of nature, I shall 

 proceed to consider more particularly what is called chemical attraction or affinity, 

 upon which depends the immediate combination of the elementary bodies with 

 each other. 



Chemical affinity only takes place at insensible distances — this may be shewn by 

 putting carbonate of soda and tartaric acid in powder together. Although the 

 particles of each appear to be in contact, yet no union takes place so long as they 

 remain dry, but on the addition of water, which dissolves them, and brings their 

 particles into closer contact, then chemical union is effected. Cohesive attraction 

 must be overcome before chemical aflSnity can take place — this is sometimes 

 effected by heal, as when copper and zinc are melted together to form brass. That 

 one or both of the substances to be united should be in a liquid state, was formerly 

 laid down as a chemical axiom, " Corpora non agunt nisi sint fluida ;" but to 



