78 Mr. G. M. Whipple on [Feb. 7, 



perature of each barometer being also noted by the observer at the 

 time of observation. 



On the 25th and 26th of April Messrs. Ellis, Nash, and other Green- 

 wich observers made a set of nine comparisons, and on the latter day 

 Messrs. Baker and Foster, two Kew observers, went to Greenwich and 

 made twelve comparisons of the five instruments, and then dismounted, 

 packed, and brought them back to the Kew Observatory, again sus- 

 pending them in their places. 



On April 27th the four hack barometers (to use a term happily 

 suggested by Mr. Galton) were again read twelve times with the Kew 

 standard of reference barometer, Newman 34, by the same three Kew 

 observers. The result of this set of comparisons shows the mean 

 difference between Kew and Greenwich to have been (Greenwich — 

 Kew)=+ -0016 inch. 



2nd Comparison. 



The four hack barometers were again on the 1st of May compared 

 at Kew with Newman 34, and then conveyed to Greenwich, where 

 they were put up in the same place as before, and read again in a 

 similar manner to that employed on the occasion of the previous 

 visit. 



On the 1st the Kew assistants made twelve sets of readings ; on the 

 2nd and 3rd the Greenwich observers made twelve sets of comparisons. 

 On the 4th we made a like number of sets, returning the instruments 

 subsequently to Kew, where they were read on the 5th with the Kew 

 standard of reference. 



The result of the second series of comparisons gives a mean dif- 

 ference (Greenwich — Kew) + 0*0007 inch. 



3rd Gomjparison. 



Before making this comparison the tube of Adie 655 was accidentally 

 broken, and having been repaired and refilled, its index error was 



C C 



somewhat changed ; also barometers Negretti and Zambra— — and —— 

 & b 429 431 



having been removed from the Observatory by the makers, two other 



instruments, also by Negretti and Zambra, Nos. f 903 and f 1105, 



were selected with which to make the comparisons. 



On the 14th May these four barometers were all compared ten times 



with the Kew barometer (Newman 34), the observers being the same 



as before. 



The next day they were taken to Greenwich, and hung up in the 

 usual place. Due time having been allowed for them to become 

 settled, and the temperature equalised, ten sets of readings were made 

 precisely in a similar manner to the previous ones. 



