ON THE PHYSICAL VIEW OF NATURE. 



161 



portion as experimental science has taken the place of 

 that purely mathematical treatment which obtained at 

 the beginning of the century, notably in the Continental 

 schools, and which thought it could exhaust the infinite 

 variety of natural phenomena by a few easily defined 

 properties measured by constants. The narrowness of 

 this view has been gradually overcome by the influence 

 of the great experimental philosophers in this country, 

 and the independent development of chemical research 

 abroad. Beside Faraday must be especially named Thomas 

 Graham 1 and Thomas Andrews, whose original experi- 39. 



Graham and 



ments did so much to extend and deepen our knowledge Andrews, 

 of the less obvious properties of matter. Graham car- 

 ried on, between 1825 and 1850, extensive experiments 

 on the diffusion of liquids and gases, on absorption, and 

 on the phenomena of osmosis or gradual filtering of sub- 

 stances through porous partitions, showing how in liquids 

 motion and pressure exist similar to that which is now 



1 Thomas Graham (1804 - 69), 

 for many years professor at Uni- 

 versity College, London, then 

 Master of the Mint, cultivated the 

 unexplored regions of physics and 

 chemistry in an original spirit and 

 yet with very simple apparatus, 

 some of which is still used under 

 his name. His ingenious labours 

 attracted the attention of Liebig, 

 through whose influence was brought 

 about the translation of ' The Ele- 

 ments of Chemistry ' into Ger- 

 man by Otto. This work in its 

 subsequent enlarged editions has 

 formed for sixty years, next to 

 Gmelin's ' Handbook,' a corner- 

 stone of chemical literature in 

 Germany, where Graham's name 

 is a household word. The dis- 

 coveries of Graham on the move- 



VOL. II. 



ment and " miscibility " of gases 

 led to the well-known law, " that 

 the diffusion rate of gases is in- 

 versely as the square root of their 

 density." From gases he advanced 

 to the more complicated study of 

 liquids, divided bodies into two 

 classes, " crystalloids " and " col- 

 loids," studied the " transpiration " 

 of gases through fine tubes, and 

 their " osmosis " or gradual filtering 

 through porous (and many ap- 

 parently non - porous) partitions. 

 In many directions he anticipated 

 later discoveries and collected in- 

 valuable materials for subsequent 

 theories. Inter alia, he established 

 the existence of " alcoholates," 

 compounds analogous to "hydrates," 

 and maintained the metallic nature 

 of hydrogen. 



