xxv.] ACCOKDANCE OF THEORIES. 569 



Clausius, 1 Favre and other experimentalists have made 

 determinations by less direct methods. Experiments on 

 the mechanical properties of gases give 426 kilogram- 

 metres as the constant ; the work done by a steam-engine 

 gives 413 ; from the heat evolved in electrical experiments 

 several determinations have been obtained ; thus from 

 induced electric currents we get 45 2 ; from the electro- 

 magnetic engine 443 ; from the circuit of a battery 420 ; 

 and, from an electric current, the lowest result of all, 

 namely, 4OO. 2 



Considering the diverse and in many cases difficult 

 methods of observation, these results exhibit satisfactory 

 accordance, and their mean (423-9) comes very close to 

 the number derived by Dr. Joule from the apparently 

 most accurate method. The constant generally assumed 

 as the most probable result is 423*55 kilogrammetres. 



Eesiducd Phenomena. 



Even when the experimental data employed in the 

 verification of a theory are sufficiently accurate, and the 

 theory itself is sound, there may exist discrepancies 

 demanding further investigation. Herschel pointed out 

 the importance of such outstanding quantities, and called 

 them residual phenomena. 3 Now if the observations and 

 the theory be really correct, such discrepancies must be 

 due to the incompleteness of our knowledge of the causes 

 in action, and the ultimate explanation must consist in 

 showing that there is in action, either 



(i) Some agent of known nature whose presence was 

 not suspected ; 



Or (2) Some new agent of unknown nature. 



In the first case we can hardly be said to make a new 

 discovery, for our ultimate success consists merely in 

 reconciling the theory with known facts when our in- 

 vestigation is more comprehensive. But in the second 

 case we meet with a totally new fact, which may lead us 



1 Clausius in Philosophical Magazine, 4th Series, vol ii. p 119. 



2 Watts' Dictionary of Chemistry, vol. iii. p. 129. 



3 Preliminary Discourse. 158, 174. Outlines of Astronomy, 4th 

 edit. 856. 



