KXAMTLES OF THE FOUR METHODS. 249 



of souiul. Tlu' iiKjuirv into tlio cause of soiiiul had led to coiielusioiis 

 respecting its mode of propagation, from which its vehxity in the aix* 

 couhl he precisely calculatecl. The c^dculations were performed; 

 but, when compared with fact, though the agreement was quite suffi- 

 cient to show the general cttrrectuess of the cause and mode of propa- 

 gation assigned, yet the loholc velocity could not be shown to arise 

 from this theory. There was still a residuid velocity to be accounted 

 for, which placed dynamical philosophers for a long time in a great 

 dilemma. At length Laplace struck on the happy idea, that this 

 might arise from the heat developed in the act of that condensa- 

 tion which necessarily takes place at every vibration by which sound 

 is conveyed. The matter was subjected to e.xact calculation, and 

 the result was at once the complete explanation of the residual phe- 

 nomenon, and a striking confirmation of the general law of the devel- 

 opment of heat by compression, under circumstances beyond artificial 

 imitation." 



" Many of the new elements of chemistry have been detected in the 

 investigation of residual phenomena. Thus Arfwedson discovered 

 lithia by perceiving an excess of weight in the sulphate j)roduced from 

 a small portion of what he considered as magnesia present in a mineral 

 he had analyzed. It is on this principle, too, that the small concen- 

 trated residues of great operations in the arts are almost sure to be the 

 lurking places of now chemical ingredients : witness iodine, brome, 

 selenium, and the new metals accompanying platina in the expeiu- 

 ments of Wollaston and Tennant. It was a happy thought of Glauber 

 to examine what everybody else threw away."* 



The disturbing effects mutually produced by the earth and planets 

 upon each other's motions were first brought to light as residual phe- 

 nomena, by the ditference which appeared between the observed 

 places of those bodies, and the places calculated on a consideration 

 solely of their gravitation towards the sun.' It was this which deter- 

 mined philosophers to consider the law of gravitation as obtaining be- 

 tween all bodies whatever, and therefore between all particles of 

 matter ; their first tendency having been to regard it as a force acting 

 only between each planet or satellite and the central body to Vvhose 

 system it belonged. Again, the catastrophists, in geology, be their 

 opinion light or wrong, support it upon the plea, that after the effect 

 of all causes now in operation has been allowed for, there remains in 

 the existing constitution of the earth a large residue of facts, proving 

 the existence at former periods either of other forces, or of the same 

 forces in a much greater degree; of intensity. To add one more 

 example : if it be possible to establish, what is generally rather as- 

 sumed than proved, that there is in one human individual, one sex, or 

 one race of mankind over another, an inherent and inexplicable supe- 

 riority in mental faculties, this must bo proved by subtractingfrom the 

 differences of intellect which we in fact see, all that can be traced by 

 known laws either to the ascertained differences of physical organiza- 

 tion, or to the differences whi<;h have existed in the outward circum- 

 stances in which the subjects of the comparison have hitherto been 

 placed. Wliat these causes might fail to account for, would constitute 

 a residual phenomenon, which and which alone would be evidence of 



* HERsCHEr., ul supra, pp. 78-9, and 86. 

 I I 



