Prof. Kelland on the Theory of Molecular Action, 263 



I now bid adieu to my theory of galvanism and my formulae 

 and to those who have neither time nor inclination to dive 

 into these mysteries, I would say, — remember, in all operations 

 that the sum of the resistances does not exceed the sum of the 

 intensities ; and that in increasing the circuit, every part is 

 equally enlarged : — to those who have devoted themselves to 

 these properties — remember they will be useless if not brought 

 into active operation ; thus, if any difficulty occurs in your 

 voltaic circuit, refer it at once to its proper head, and the 

 operator may be sure that a continual practice and habit of 

 using these formulas will enable him to conduct his proceedings 

 with a certainty never obtainable by blind experiment. 



In concluding these formulae, I herewith leave theory and 

 rationale altogether, for having completed the principles, as 

 far as I am capable, of everything relating to electro-metal- 

 lurgy, I shall enter at once into the applications of the science 

 for the direct purposes of the arts ; and although everything 

 that will be contained in the subsequent parts of this work has 

 already been .comprised in the parts already finished, yet there 

 are many little practical difficulties to be surmounted — many 

 little circumstances to be pointed out which the operator is 

 likely to overlook or forget in conducting his operations, and 

 these are the circumstances to which the concluding pages 

 will more especially be devoted. Henceforth the work will 

 be entirely practical, as heretofore it has been exclusively 

 theoretical. There is a reproach attached to the very word, 

 theory ; the sense in which it is employed means rather ratio- 

 nale than theory, for whilst it has been my constant endea- 

 vour to shun theories without facts, I have tried and tried 

 hard to generalize all extensive series of facts, and to give the 

 rationale of every circumstance which is likely to occur to the 

 operator. 



XLV. Reply to some Objections against the Theory of Mo- 

 lecular Action according to Newton's Law. By the Rev. P. 

 Kelland, M.A., F.R.SS. L. $ E., F.C.F.S., $c, Professor 

 of Mathematics in the University of Edinburgh, late Fellow 

 and Tutor of Queen's College, Cambridge. 

 [Continued from p. 208.] 



MR. EARNSHAWS first argument is, " Dispersion in 

 a refracting medium cannot be accounted for on the finite- 

 interval theory, unless there be also dispersion in vacuo. Now 

 as there is no dispersion in vacuo, I infer generally, that the 

 finite-interval theory cannot account for dispersion" (pres. vol. 

 p. 47). 



The difficulty which is here brought forward is the same 



