96 Mr. S. U. Pickering on Mr. Lupton's Method of 



need only answer Mr. Lupton, as I did Arrhenius, by chal- 

 lenging him to point out one single equation or one single 

 constant in the whole of my papers. 



6. Of the objections which Mr. Lupton considers " impugn 

 the extreme accuracy of the experimental results " (p. 425), but 

 which apparently, " even if admitted, do not impugn their 

 great accuracy"* (p. 429), the first is, that these results do not 

 agree with those quoted by Mendeleefff. This is incorrect ; 

 I clearly stated that the latter " showed such a very good 

 general concordance with my own results that they may be 

 taken together with these as affording a further illustration 

 of the effect of temperature on the figure" (loc. cit. p. 79). 

 It was only in my interpretation of the results that I dif- 

 fered from Mendeleeff ; and if Mr. Lupton will but compare 

 together the two figures on page 81, loc. cit., I scarcely think 

 that he will say that I was not justified in doing so, or that 

 the accuracy of my results is impugned by the expression of 

 this difference of opinion. 



7. Mr. Lupton alludes to the well-known objections against 

 the piknometer. I have nothing to say in favour of this 

 instrument in its usual imperfect form : the only question 

 worth considering is whether the particular instrument which 

 I used gave correct results or not, and I have given Mr. 

 Lupton ample means for judging for himself on that point. 

 I have shown that the error was less than that which might 

 reasonably be attributed to the errors of the balance and 

 thermometer used, that they were as small as those expe- 

 rienced by the best experimentalists when using a Sprengel 

 tube, and moreover that the actual values which I obtained 

 with water at different temperatures agreed most completely 

 with those of Kopp and Pierre (loc. cit. p. 70, and Phil. Mag. 

 xxx. p. 406). It may be worth mentioning that the only one 

 of the well-known objections to the ordinary piknometer which 

 Mr. Lupton cites is a mistaken objection, namely " that the 

 stopper does not go in to exactly the same position when un- 

 equally pressed." Such a defect would cause an error which 

 would be greater the greater the density of the liquid used ; 

 whereas the reverse is the case, as Mr. Lupton might have 

 ascertained by experiments with a faulty bottle. The real source 

 of inaccuracy in density-bottles is the fact that the imperfect 



* The italics are Mr. Lupton 's. 



t Mr. Lupton quotes me as having said " MendeleefFs values ; " but I 

 was careful to point out that the values used by Mendeleeff were col- 

 lected from the results of other physicists (pp. 66, 79). It would ill 

 become me to impugn the accuracy of any of Mendeleeft's own deter- 

 minations. 



