SIE B. C, BEODIE 0^' THE CALCULUS OF CHEMICAL OPEEATIONS. 783 



In our present system these signs have been replaced by letters marking the weights 

 of the atoms, and the circles have been removed. But no fundamental change has been 

 made in his conception, and in the arrangement of letters Hg, O2, H2O and the like, we 

 still retain the image of Dalton under another form. Indeed where special clearness 

 is required we not unfrequently find the circles restored to the picture ; and the most 

 recent representation of the nature of matter consists in a modification of this concrete 

 symbol to meet the necessities of modem ideas*. On this view that arrangement of 

 letters in the symbol which we call a formula is to be regarded as a figure by which the 

 arrangement of atoms in the substance is represented ; the symbolic system being a sort 

 of orreryf, in which is imperfectly imitated the structure and movements of that unseen 

 molecular world, on the mechanism of which chemical transformations are assumed to 

 depend. A still more exact comparison would perhaps be to a diagram of Euclid, which 

 bears a certain, though a confessedly inexact, resemblance to the object signified, and 

 serves by this likeness to bring it vividly before the imagination:}:. 



This molecular interpretation is, it must be admitted, rather a matter of tacit con- 

 vention than of express statement, and the above remarks, without qualification, would 

 be too general. For it is a striking feature in our science that no system of chemical nota- 

 tion has yet been devised of such a nature as to receive universal and unqualified assent, 

 or even a uniform interpretation. Berzelius §, who is generally regarded as the originator 

 of our present method, considered that the letters which he employed simply represented 

 certain weights of matter, and that in the symbol of a chemical substance the sign -|- was 



* See EEKXTii, ' Lehrbuch der organischen Chemie,' 1861, p. 160, where the following diagrams are given : — 



Hydrochloric acid . . (pjO 



Water C^ 



@® 



Anunonia W><>< 



Nitric acid S-c><><><> 



Oxygen 



o 

 o 



t " But formulse may be iised in an entirely different and yet perfectly definite manner, and the use of the 

 two distinct points of view will perhaps not be unserviceable. They may be used as an actual imago of what 

 we rationally suppose to be the arrangement of the constituent atoms in a compound, as an orrery is an image 

 of what we conclude to be the arrangement of our planetary system." — " On the Constitution, of Salts," by A. "W. 

 WiiiiAiisoN, Journal of the Chemical Society, vol. iv. p. 351. 



J An interesting account of the development of our present system of notation, and its relation to the atomic 

 theory, is given in the article " Notation " in Wattb's Dictionary of Chemistry, by Professor G. C. Fostek. 



§ Bekzeuus, ' Trait<S dc Chimie,' 1845, vol. i. p. 119; and ' Jahresbericht,' voL xv. p. 201. 



•5o2 



