THE EXACT MEASUREMENT OF PHENOMENA. 325 



bisulphide, and other media, so that unless general laws 

 can be detected, this one phenomenon of solution can 

 never be exhaustively treated. The same kind of questions 

 recur as regards the solution or absorption of gases in 

 liquids, the pressure as well as the temperature having 

 then a most decided effect, and Professor Roscoe s re 

 searches on the subject present an excellent example of 

 the successive determination of various complicated laws 11 . 



There is hardly a single branch of scientific research 

 in which similar complications are not ultimately en 

 countered. In the case of gravity, indeed, we arrive at 

 the final law, that the force is invariably the same for all 

 kinds of matter, and depends only on the distance of 

 action. But in other subjects the laws, if simple in their 

 ultimate nature, are disguised and complicated in their 

 apparent results. Thus the effect of heat in expanding 

 solids, or the reverse effect of forcible extension or com 

 pression upon the temperature of a body, will vary 

 from one substance to another, will vary as the tem 

 perature is already higher or lower, and will probably 

 follow a highly complex law, which in some cases gives 

 negative or exceptional results. In crystalline substances 

 the same researches have to be repeated in each distinct 

 axial direction. 



In the sciences of pure observation again, such as those 

 of astronomy, meteorology, and terrestrial magnetism, we 

 meet with many interesting series of quantitative deter 

 minations. The so-called fixed stars, as Giordano Bruno 

 divined, are not really fixed, and may be more truly 

 described as vast wandering orbs, each pursuing its own 

 path through space. We must then determine separately 

 for each star the following questions : 



1 . Does it move 1 



2. In what direction I 



Watt s Dictionary of Chemistry, vol. ii. p. 790. 



