obtained by Combinations of Different Interferometers* 135 



of the interferometer does not indicate the true temperature 

 of the air. The coordinates of interference points were 

 read by means of a micrometer microscope detached from a 

 geodetic comparator, one division of the drum being equi- 

 valent to lfi, which reduced to angular measure in the 

 focal plane of the photographic objective was equivalent to 



The following measurements were made for the difference 

 in wave-lengths between the satellites —242 and +123 of 

 the green line, the appearance of the nearly coincident points 

 being given in PI. I. fig. 3. 





e. 



P'-P. 



(P'-P)-. 

 v 'in 



P'S. 



8\. 



PI. No. 7... 



49-081 mm. 



12 



(T) +0-00029 



+0-01468 



365-0 m.A.U. 









(N)+ 0-00029 



+001851 



365-1 „ 



PL No. 10... 



49-085 mm. 



12 



(T) +0-00039 



+001320 



3649 









(N) +0-00039 



+001581 



3650 „ 



PI. No. 21... 57-180 mm. 



14 



(T) +0-0001 2 



-0-00121 



365-0 „ 







(N)+0-00012 



+0-00267 



3651 „ - 



PI. No. 43...;57'161 mm. 



14 



(T) +0-00034 



-0-00320 



365-1 







(N) +0-00034 



-000255 



365-1 



These measurements show that the first decimal place of 

 m.A.U. is generally reliable. By crossing the Lummer- 

 Gehrcke plate with the Fab ry-Perot interferometer, we found 

 8\— 364-4 m.A.U. for these two lines. The discrepancy 

 between the two will have close connexion with the discussion 

 raised by Kolacek already mentioned. 



When P ; — P is large more exact values can be obtained. 

 The following example gives the difference in wave-lengths 

 between the yellow lines of mercury : — 





e. 



P'-P. 



$\(A.U.). 



PI. No. 72 



16-8194 mm. 



212 



(T) 21-0610 



PI. No. 92 



16-7364 mm. 



211 



(T) 21-0610 



(N) 21 -0605 



PI. No. 115 



48-9892 mm. 



618 



(Tj 21-0610 

 (N) 21-0607 



PI. No. 117 



48-9894 mm. 



618 



(T) 21-0607 









(N) 210611 



