222 Prsesepe Group; Measurement and Reduction 



Schlesinger : Kretz : 



v = — 0.00017 mm. v = — 0.00025 »nm. ■ 



± 0.000034 ± 0.000030 



These two values are not very accordant, but they agree suffi- 

 ciently well for present purposes. As, however, some doubts 

 were entertained as to whether the plates had been thoroughly 

 cooled in the intervening three hours, and as to whether it 

 would not be better to measure the distance between the 

 specks at a season when artificial heat could be entirely dis- 

 pensed with, the following third series of observations was under- 

 taken by myself, several days elapsing between the various 

 measurements. No artificial heat was allowed in the measuring 

 room during the whole period. 



May 20, 1897. Temperature = 73. °6. 

 104.1530 mm. 

 10 

 18 





30 





58 





48 





25 





68 



Mean, 



104.1536 ± 0.00047 



May 22, 1897. 



Temperature = 69. °6. 





104.1534 mm. 





36 





26 





44 





34 





39 





54 





76 



Mean, 



I04.I543 ± O.OOO36 



May 29, 1897. 



Temperature = 71. °o. 





104.1548 mm. 





26 





28 





64 





34 





28 





36 





34 



Mean, 104.1537 =b 0.00031 



