Comparison of Magnetic Instruments at Kew Observatory. 157 



Taking into consideration the above facts, and the further fact 

 that M. Moureaux's visit occurred at the end of a month, it was 

 decided to standardise the curves exclusively from Mr. Baker's 

 special observations, on July 27 to 29. These gave three or more 

 complete determinations of each element, under conditions which 

 might be described, on the evidence of the curves, as an almost per- 

 fect magnetic calm. 



Mr. Baker's absolute observations and the corresponding curve 

 measurements were in good agreement, especially in the case of the 

 horizontal force, where the individual calculated values for the base 

 line of the curves showed no difference greater than 0*00002 C.G.S. 

 unit. 



Owing to the less direct method of comparing the inclinometers, 

 I regard the results obtained for them as somewhat less trustworthy 

 than the others. 



The figures under the heading " Observatory — Moureaux " are to 

 be regarded as the excess in the readings of the absolute Kew instru- 

 ments over those of M. Moureaux's instruments, supposing the 

 former to have been read simultaneously with the latter. The 

 times specified are actually those occupied by M. Moureaux's obser- 

 vations. 



Declination. 







Kew 





Observatory — 



Date. 



Time. 



Observatory. 



Moureaux. 



Moureaux. 



July 26 



3.47— 4.2 p.m. 



17° 5-9' 



17° 5-7' 



+ 0-2' 



" 27 



10.5 —10.18 A.M. 



4-8 



5-0 



-0-2 



27 



10.22—10.32 „ 



60 



5-7 



+ 0-3 



28 



9.9 — 9.24 „ 



21 



1-3 



+ 0-8 



28 



9.28— 9.40 „ 



30 



1-9 



+ 1-1 



29 



11.37—11.49 „ 



99 



93 



+ 0-6 

















Horizontal Force.* 













Observatory — 







Kew 





Moureaux. 







Observatory. 



Moureaux. (Unit being 10~ 5 



Date. 



Time. 



C.G-.S. 



C.G-.S. 



C.G-.S. unit). 



July 26 



4.13— 4.42 p.m. 



0-18354 



0-18356 



- 2 



27 



10.41—11.10 A.M. 



25 



24 



+ 1 



28 



9.48—10.18 „ 



28 



49 



-21 



28 



10.43—11.11 „ 



20 



39 



-19 



29 



10.24—10.56 „ 



20 



43 



-23 



29 



11.1 —11.31 „ 



20 



27 



- 7 • 









Mean. . . . 



-0-00012 C.G-J 



unit. 



* [jSov. 15, 1897. M . Moureaux requests me to explain that in the present com- 

 parison of horizontal force at Kew — as well as in his recent comparisons at 



