1S6 The Foundations of Physical Science. 



changeable particles/' is assuredly not ascertained to be true, and 

 there was not the slightest occasion to make a doubtful guess, 

 as in the word we have given in italics, or it may be an 

 erroneous assertion, the foundation of a superstructure built up 

 in accordance with logical rules. So distinctly does Dr. Arnott 

 assert the doubtful doctrines connected with the word atom, 

 that he gives as an illustration of the assertion, just cited, the 

 case of a piece of metal, bruised, broken, cut, dissolved or 

 otJierwise transformed, a thousand times, but which still " can 

 always be exhibited again as perfect as at first." Dr. Arnott 

 probably did not intend to convey all that this passage plainly 

 means and implies, and he would surely hesitate to affirm all 

 its unproved assertions, if they were drawn up in due form 

 and presented to his eye. He does not hiow that there are 

 such things, for example, as <c indestructible unchangeable 

 particles" of iron. There could only be such particles of simple 

 substances, and who can tell what substance really deserves 

 that name t All compound substances may have an atomic com- 

 position — that is to say, they may not be susceptible of division 

 beyond a certain limit without being decomposed ; but if so, 

 the smallest possible particle of a compound will consist of 

 two or more still smaller particles of its elements, whatever 

 they may be. The principles of mechanics do not depend upon 

 any of the gratuitous assertions made in Dr. Arnott' s so called 

 " first fundamental truth,'' and it does not coincide with his 

 usually careful and luminous statements concerning either 

 argument or fact. 



An accural e knowledge of the elementary principles and 

 facts of physics forms the only possible foundation for the study 

 of more complicated' branches of physical science, and it is 

 unfortunately surprising to find how feAV persons have taken the 

 trouble — or, if Dr. Arnott were the guide, we should say 

 enjoyed the pleasure — of learning these primary truths. 



The processes of the tinman organism developc many 

 forces, but man as a worker creates none; all that he can 

 accomplish is to use his own muscular force, or some other 

 power, so as to accomplish bis will. If he boils water ami 

 avails himself of the expansive force of steam, lie has not made 

 ihiii force. !!•• bas merely placed fuel, water, certain masses 

 <>f metal mid other articles so as to be acted upon, in given 

 directions and lor a, given time, by certain properties of beat. 



In what are catted the mechanical powers (level's, etc.) lie does 



somewhat less, and his action depends upon a lew simple 

 principles ami facts. This is well expressed in the opening 

 lines of the analysis to the second section of Dr. Arnott's 

 work : — "The bodies or musses composing the universe may bo 

 at rest or motion, and to change any present state, force 



