1 72 Mr. P. Jenkin on the Question of the 



nearly the same time ; they were both extremely well adjusted, 

 as I stated at that time in my Report ; andj am not aware that 

 since 1862 any material advance has been made in the adjust- 

 ments. 



I do not quite understand whether Dr. Siemens means to state 

 that the coils called by me " Siemens, London/' had been only 

 roughly adjusted by the method of weighing in 1859 and then 

 readjusted in 1862 before exhibition; but whatever be the case, 

 the two sets were equally well adjusted when exhibited, and as 

 good in themselves as any set of coils I have since 'seen. The 

 charge therefore of unfairness in publishing observations on 

 rude coils, made by an imperfect method, arises from some mis- 

 take of Dr. Siemens as to the condition in which the coils were 

 when exhibited by the London firm. Moreover let me point 

 out that in the Report referred to I give the values of coils 

 adjusted by Mr. White of Glasgow in 1859, under Prof. Thom- 

 son's supervision, and also exhibited in 1862. These are, and 

 were, in excellent adjustment, with the exception of one coil. 

 They were subjected to the same treatment as to travelling and 

 use as Messrs. Siemens's coils; and I will not do Messrs. Sie- 

 mens the injustice to suppose that in 1859, when the coils ex- 

 hibited were first made, they knew less of the art of copying 

 resistances than we did in England. 



This value of Prof. Thomson's old unit, based on the old 

 1859 coils, has been repeated by me in every Table published, 

 although it tells against the absolute unit as a standard, about 

 as much as Messrs. Siemens' s old coil tells against the mercury 

 unit. Similarly I have repeated Weber's various discrepant 

 determinations. 



To resume. No serious error could have occurred in my ex- 

 periment without being corrected by Messrs. Siemens at the 

 time, for which they had every opportunity. The coils were not 

 rudely adjusted when exhibited, nor were they even originally 

 made at the time when the art of copying resistances was scarcely 

 known. No explanation of the difference which could be sub- 

 stantiated was given me, and I believed that the difference was 

 probably due to bad reproduction ; but I abandon that opinion 

 since I understand Dr. Siemens to say that no change in the 

 standard has been made. I have only repeated their value in 

 Tables in which I repeated still worse discrepancies in so-called 

 absolute determinations, and in which the value of coils as old 

 as those of Dr. Siemens were also given. 



Dr. Siemens has himself allowed that the standard in 1864 

 did not, even by his experiments, truly represent his definition 

 within 0*287 per cent. Surely it was no unfair criticism to 

 point this out; and this is the only point urged by me in the 



