WUEWELL'S WRITINGS AND CORRESPONDENCE. 

 On this Mr Todhuntar very properly observes : 



"Of wm Uwr* to practical uncertainty a* to this principle; but Dr \VTicwell seems to allow 

 lu nadm to ioMCtM IfcM it ia of the came nature as the axiom that 'two straight lines cannot 

 iaeloip a mea,' TU*e u, however, a wide difference between them, depending on a fact which 

 Dr Wtowvil baa Mm** 1 * raooynued in another place (nee vol. i. p. 224). The truth is, that strictly 

 i-miidf UM weight of the whole compound is not equal to the weight of the separate elements; 

 for UM weight ittfW** upon the poaition of the compound particles, and in general by altering 

 UM poeitiaa of UM particle*, the resultant effect which we call weight is altered, though it may 

 he to an inappreciable extent" 



It U evident that what Dr Whowell should have said was : " The mass of 

 the whole compound must be equal to the sum of the masses of the separate 

 elements." This statement all would admit to be strictly true, and yet not a 

 single experiment has ever been made in order to verify it. All chemical 

 measurements are made by comparing the weights of bodies, and not by com- 

 paring the forces required to produce given changes of motion in the bodies ; 

 and as we have just been reminded by Mr Todhunter, the method of comparing 

 quantities of matter by weighing them is not strictly correct. 



Thus, then, we are led by experiments which are not only liable to error, 

 hut which are to a certain extent erroneous in principle, to a statement which 

 is universally acknowledged to be strictly true. Our conviction of its truth must 

 therefore rest on some deeper foundation than the experiments which suggested 

 it to our minds. The belief in and the search for such foundations is, I think, 

 the most characteristic feature of all Dr Whewell's work. 



