EXAMPLES OF T*HE tOVU METHODS. 



281 



when compared with fact, though the 

 agreement was quite sufficient to show 

 the general correctness of the cause 

 and mode of propagation assigned, yet 

 the whole velocity could not be shown 

 to arise from this theory. There was 

 still a residual velocity to be accounted 

 for, which placed dynamical philoso- 

 phers for a long time in 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 exact calculation, and the result 

 was at once the complete explanation 

 of the residual phenomenon, and a 

 striking confirmation of the general 

 law of the development of heat by 

 compression, under circumstances be- 

 yond 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 produced from a small por- 

 tion of what he considered as magnesia 

 present in a mineral he had analysed. 

 It is on this principle, too, that the 

 small concentrated residues of great 

 operations in the arts are almost sure 

 to be the lurking-places of new chemi- 

 cal ingredients : witness iodine, bro- 

 mine, selenium, and the new metals 

 accompanying platina in the experi- 

 ments of Wollaston and Tennant. It 

 was a happy thought of Glauber to 

 examine what everybody else threw 

 away." * 



" Almost all the greatest discoveries 

 in Astronomy," says the Bameauthor,+ 

 •' have resulted from the consideration 

 of residual phenomena of a quantita- 

 tive or ujmerical kind. ... It was 

 thus that the grand discovery of the 

 precession of the equinoxes resulted 

 as a residual phenomenon from the 

 imperfect explanation of the return of 

 the seasons by the return of the sun 

 to the same apparent place among 



* Discourse, T>p. 156-158, and 171. 

 t Ouiliius oj Astronomy, § 856. 



the fixed stars. Thus, also, aberra- 

 tion and nutation resulted as residual 

 phenomena from that portion of the 

 changes of the apparent places of the 

 fixed stars which was left unaccounted 

 for by precession. And thus again 

 the apparent proper motions of the 

 stars are the observed residues of 

 their apparent movements outstand- 

 ing and unaccounted for by strict 

 calculation of the effects of preces- 

 sion, nutation, and aberration. The 

 nearest approach which human theories 

 can make to perfection is to diminish 

 this residue, this caput mortuum of 

 observation, as it may be considered, 

 as much as practicable, and, if pos- 

 sible, to reduce it to nothing, either 

 by showing that something has been 

 neglected in our estimation of known 

 causes, or by reasoning upon it as a 

 new fact, and on the principle of the 

 inductive philosophy ascending from 

 the effect to its cause or causes." 



The disturbing eflfects mutually pro- 

 duced by the earth and planets upon 

 each other's motions were first brought 

 to light as residual phenomena, by 

 the difference which appeared between 

 the observed places of those bodies 

 and the places calculated on a con- 

 sideration solely of their gravitation 

 towards the sun. It was this which 

 determined astronomers to consider 

 the law of gravitation as obtaining 

 between 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 whose system 

 it belonged. Again, the catastro- 

 phists, in geology, be their opinion 

 right or wrong, support it on 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 exist- 

 ence at former periods either of other 

 forces, or of the same forces in a much 

 greater degree of intensity. To add 

 one more example : those who assert, 

 what no one has shown any real 



