Mr Exley''s Prmciples of Natural Philosophy. 351 



able men, and that it threatens to become an epidemic in the once salubri- 

 ous fields of physical inquiry. 



Within the last two or three years no fewer than three works of this kind 

 have been given to the world. The first of these, published in 1827, by 

 our able countryman Dr Blair, is entitled, ScienUfic Aphorisms, being 

 the outline of an attempt to establish fixed principles of Science ; and to ex- 

 plain from them the general nature of the construction and mechanism of the 

 material system, and the dependence of that system on mind. This work 

 evinces great knowledge and profound thought ; and may be read with ad- 

 vantage by those who cannot adopt the hypotheses of jaculatory atoms, 

 and molecules with spinous processes. The next work of this kind is the 

 Explication Universelle by H. Azais, with the imposing motto of Tout 

 expliquer, cest tout unir. In this work, which is one of the highest pre- 

 tensions, the author does not limit himself, like our grave countryman, to 

 the constitution merely of compound bodies. The heavens above, and the 

 earth beneath, and all things under the earth, present no difficulties to hi» 

 reasoning imagination. The movements of the planets, the puzzles of 

 animal and vegetable life, and the conformation of the soul itself, are all ex-, 

 plained in a Paris garden, to crowded audiences, and admiring disciples. 



The third work to which we have alluded, is that of Mr Exley, which 

 is of an intermediate character, neither ballasted by the patient thought 

 of the Scotch philosopher, nor buoyed up by the levities of the French 

 lecturer. Mr Exley unites mathematical acquirements with an extensive 

 knowledge of chemistry and physics, and as he describes every phenomenon 

 in a separate paragraph, and then adds its explanation, the reader may col- 

 lect a good deal of information by reading the details of the separate phe- 

 nomena, even though he overlooks the speculative views which tread upon 

 their heels. But while we make this admission in favour of Mr Exley, we 

 must at the same time declare, that, like all theorists, he often states only 

 what he thinks he can explain, and thus presents important physical facts in 

 a meagre and a mangled form. 



If we thought it would be either instructive to our readers, or useful to 

 Mr Exley, we should give various specimens of his descriptions of pheno- 

 mena, and point out not only their imperfections, but the absolute defects of 

 the explanations which he has given of them- We shall content ourselves 

 with a single specimen, which relates to one of the most curious and well 

 known facts in science, and which embraces the consideration of properties, 

 both chemical and physical, viz. the production of the prismatic colours on 

 steel, by raising it to different temperatures. 



" Phenomenon 50. In raising the temperature of the steel through va- 

 rious degrees, it assumes successively the prismatic colours- 



" Explanation. As the temperature is raised, the superficial atoms 

 are more and more separated, and the enclosed ethereal atoms become 

 more and more diffused as the heat increases ; hence the surface acquires 

 different conditions for the reflection of different sorts of ethereal atoms,"" 

 and the different colours, doubtless, arise from the differences in the* 

 forces and spherules of the ethereal matter which constitutes light, toge-; 



