130 Prof. Nagaoka and Mr. T. Takamine on Crossed Spectra 



lie in horizontal rows and vertical columns. This is the 

 most convenient position for observation. By adjusting 

 the thickness of the air-plate, we can bring the interference 

 points due to a special line, which we wish to study, in 

 different positions with respect to the line of reference. 

 This combination is sometimes convenient for determining 

 a small difference in wave-lengths, for example, the relative 

 position of satellites. The crossed spectra of the green line 

 of mercury are shown in PL I. fig. 2. The fine structure of 

 the line is apparent at a glance, and what is more inter- 

 esting is the vagueness of the principal line, suggesting that 

 there is a structure in it, as remarked by Janicki *. The 

 accompanying diagram shows the position of the satellites 

 (%• 2). 



Fig. 2. 



A -242 



m 



\1 



=p -^ -=. ^ r 



+ SLIO 



Lunimer-Gehrcke Plate and Fabry-Perot Plate. 



The different distributions of interference points by 

 varying the thickness of air-plate present most interesting 

 features ; when the visual observation is possible, we can 

 judge from the relative displacement of interference points 

 the difference in wave-lengths, even if several orders of 

 spectra are overlapped. The method of coincidence can 

 be applied with more accuracy in the combination here 

 described than with the Fabry-Perot interferometer only. 

 From this practical point of view, the sliding interferometer 



* Janicki, loc. cit. 



