SIE B. C. BEODIE ON THE CALCULUS OF CHEMICAL OPEEATIONS. 855 



The atomic theory may be compared to a sort of " abacus" or simple mechanical instru- 

 ment which chemists have invented to facilitate their calculations. It is useless to pre- 

 tend that any demonstration can be given of this theory, which, at best, can only be re- 

 garded as a possible hypothesis suggested by the facts ; but nevertheless it has a very real 

 claim upon our consideration from the practical advantages which it has afforded in the 

 study of the science. The atoms of the chemist fulfil a similar purpose in his calculations 

 to that fulfilled by balls in the estimation of probabilities. They afford a simple and not 

 inaccurate image of the subject with which he is concerned, by which he is enabled to 

 reduce his problems to a concrete form, and thus at once to realize and to isolate them. 

 To forbid the use of such an image would be to impose a very unnecessary restriction 

 upon scientific methods. A ball as the concrete sytabol of an indivisible whole, may 

 advantageously represent, as occasion requires, a unit of weight, a simple weight, an 

 event. We are perfectly free, when it suits our purpose, to make use of such concep- 

 tions. It is, however, a fatal illusion to mistake the suggestions of fancy for the realities 

 of nature, and such a symbol becomes open to serious objection unless we carefully dis- 

 criminate between conjecture and fact. Under the baneful influence of such hypotheses 

 the methods of positive science lose their hold upon the mind, until at length we are 

 actually informed by the consistent advocates of these ideas that the science of chemistry 

 has no other field for its activity than the obscure region of atomic speculations. 



Now a symbolic calculus aflFords the same indispensable aid which is given by the 

 atomic theory, but in a more truthful and effectual way. In the place of molecules 

 and atoms it offers, as the subject of scientific contemplation, a system of marks and 

 combinations of letters, which, however, we are not free to arrange and to interpret 

 according to the dictates of caprice, but of which each has a specific meaning assigned 

 to it in the calculus, from which the laws are deduced according to which it is permitted 

 to operate upon it. We are thus enabled to construct an accurate symbolic representa- 

 tion of the phenomena before us, on the fidelity of which we can rely. Such a system 

 is indeed based, in the most absolute sense, upon fact, for it presents only two objects 

 to our consideration, the symbol and the thing signified by the symbol, the object of 

 thought and the object of sense; and it is not the least among the advantages which 

 such a method affords, that through it we are enabled to dispense altogether with less 

 truthful modes of representation, as no longer calculated to serve even a useful purpose. 



Every mark or sign which we employ for the purposes of thought is in a certain 

 sense a symbol, and in their actual system of chemical notation, chemists are already in 

 possession of an imperfect symbolic method. It appeared to me inexpedient to attempt 

 any interference with this method, which has already been subject to so many modifica- 

 tions, and which, moreover, satisfies certain real demands. I must confess also that it 

 seemed to me incapable of development, as being destitute of those essential conceptions, 

 in the growth of which the development of such a method consists. 



Now it is the introduction of the conception of chemical operations which, as has 

 before been said, especially distinguishes this calculus. ITie symbols here employed 



6z2 



