364 A SHORT HISTORY OF SCIENCE 



It may be questioned whether the celebrated periodic law of New- 

 lands, Lothar Meyer and Mendelejeff, which has brought some order 

 into the atomic and other numbers referring to the different elements, 

 and has even made it possible to predict the existence of unknown ele- 

 ments with definite properties, stands really in a firmer position than 

 the once well-known but now forgotten law of Bode, according to 

 which the gap in the series which gives the distances of the planets 

 from the sun indicated the existence of a planet between Mars and 

 Jupiter. 



CHEMICAL STRUCTURE. - - Crystallography a science of the 

 nineteenth century established an important connection be- 

 tween chemistry and geometry. Haiiy made mineralogy "as 

 precise and methodical as astronomy. . . . He was to Werner and 

 Rome de 1'Isle, his predecessors, what Newton had been to Kepler 

 and Copernicus." 



In the early years of the atomic theory Wollaston had predicted 

 that philosophers would seek a geometrical conception of the 

 distribution of the elementary particles in space a prophecy 

 first practically fulfilled by Van't Hoff s Chemistry in Space (1875). 



The chemical character is dependent primarily upon the arrange- 

 ment and number of the atoms, and in a lesser degree upon their 

 chemical nature (V. Meyer) . The atomic view first became a scientific 

 instrument, when arithmetical relations of a definite and unalterable 

 kind were proved to exist ; it became a yet more useful instrument, 

 when to the arithmetical there were added geometrical conceptions. 



M erz. 



PHYSICAL CHEMISTRY: ELECTROLYTIC AND THERMODYNAMIC 

 DEVELOPMENTS OF CHEMISTRY. In the latter part of the nine- 

 teenth century much light was thrown on a wide range of physical 

 and chemical phenomena by the study of solutions and their 

 electrolytic behavior. Much had already been accomplished by 

 Davy in the decomposition of substances by the electric current, 

 leading for example to the first isolation of the elements, sodium 

 and potassium. Faraday showed that for a given substance the 

 amount decomposed is dependent solely on the quantity of 

 electricity passed through and that for different substances the 



