474 INDUCTION. 



in the sulphate produced from a small portion 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 chemical ingredients : witness 

 iodine, brome, selenium, and the new metals accompanying 

 platina in the experiments 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 same author, f " have resulted from the consideration of 

 residual phenomena of a quantitative or numerical 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 the 

 fixed stars. Thus, also, aberration and nutation resulted as 

 residual phenomena from that portion of the changes of the 

 apparent places of the fixed stars which was left unac- 

 counted for by precession. And thus again the apparent 

 proper motions of the stars are the observed residues of 

 their apparent movements outstanding and unaccounted for 

 by strict calculation of the effects of precession, 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 possible, 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 effects mutually produced 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 consideration solely of their gravitation 



* Discourse, pp. 156-8, and 171. t Outlines of Astronomy, 856. 



