Comparison of Magnetic Instruments at Keiv Observatory. 159 



After this remark, I tliink I may safely utilise the present com- 

 parison to extend a table,* in which Professor Riicker and Mr. "W. 

 Watson embodied the results of their comparison of the standard 

 instruments at various English and Irish observatories, made by 

 means of travelling instruments, in 1895. The differences between 

 the declination, horizontal force, and inclination instruments are 

 given in order, one below the other, the unit in the case of the 

 horizontal force being 0-00001 C.G-.S. unit. 



The table is to be read as follows : — " Standard declinometer at 

 Kew reads higher than that at Pare Saint-Maur by 0'5', but lower 

 than that at Falmouth by OS'," and so on. The last column gives 

 the differences from the mean instrument, so to speak, of the five 

 observatories. 



Kew Observa- 

 tory 



Pare Saint- 

 Maur .... 



Falmouth . . . 



Stonyhurst . . 



Valencia (Ca- 

 hircrveen) 



The apparent agreement between the standard instruments at 

 Pare Saint-Maur and Stonyhurst is noteworthy. The fact that the 

 Kew standard instruments agree so closely with the imaginary mean 

 instruments was, it may be observed, not noticed by the writer until 

 after he had constructed the table. In his opinion the phenomenon 

 is probably purely -fortuitous. In searching, however, for explana- 

 tions of the discrepancies between the several instruments, or in 

 attempting to remove them, a consideration of the departures from 

 the means might be profitable. 





Pare 



Fal- 



Stony- 







Kew. 



Saint-Maur. 



mouth. 



hurst. 



Yalencia. 



Mean. 





+ 0'5' 



- 0-8' 



+ i-r 



o-o 7 







-12 



-18 



- 6 



+ 29 







+ 2-0' 



- 1-6' 



+ 2-2' 



- 1-8' 



+ 0-2' J 



- 0-5' 





- 1'3' 



+ 0-6' 



- 0-5' 



- 0-3' 1 



+ 12 - 





- 6 



+ 6 



+ 41 



+ 11 L 



- 2 0' 





- 3 -6' 



+ 0-2' 



- 3-8' 



- 1-8' J 



+ 0-8' 



+ T3' 





+ 1-9' 



+ 0-8' 



+ 1-0' "1 



+ 18 



+ 6 





+ 12 



+ 47 



+ 17 y 



+ 1-6' 



+ 3'6' 





+ 3-8' 



- 0-2' 



+ 1-8' J 



- l'l' 



- 0-6' 



- 1-9' 





- 11' 



- 0-9' ] 



+ 6 



- 6 



-12 





+ 35 



+ 5 , r 



- 22' 



- 0-2' 



- 3-8' 





- 4-0' 



- 2-0' J 



00' 



+ 0-5' 



- 0-8' 



+ 1-1' 





+ 0-2' I 



-29 



-41 



-47 



-35 





-30 )■ 



+ 1-8' 



+ 3'8' 



+ 0-2' 



+ 4*0' 





+ 2-0' J 



* ' Brit. Assoc. Report ' for 1896, p. 97. 



