﻿96 



S. P. Langley — Unrecognized Wave-lengths. 



We now consider as our second example a measurement at 

 5xAD 2 , where glass can hardly be used, and where its place is 

 supplied with the rock-salt prism, and that of the sun by the 

 arc. 



/Second example of measurement. With rock-salt prism. 

 (Extract from original record.) 



Station, Allegheny. 



Bate, April 15th, 1886 (p. m.). 



Wet bulb at 4 h 30 m (inside dark room artificially heated) = 

 21°-0 Cent. 



Dry bulb at 4 h 30 m (inside dark room artificially heated) = 

 26°-4 Cent. 



Aperture of slit S, = 4 mm . 



Aperture of slit S 2 = 1-25. 



Prism used, Hastings No. 1 (rock-salt). 



Lenses used, focus = 760 mm for visible rays. 



Grating used, Rowland No. 2. 



Galvanometer No. 3, damping magnet at 40 cm . 



Time of single vibration = 17*5 sec. with current. 



Bolometer No. 16 (aperture l mm ). 



Setting on slit — 0° 00' 00". 



Setting on B 2 (spectrum thrown east) = 41 o, 03' 00". 



Setting on Z> 2 (spectrum thrown west) = 319° 51' 40". 



Current of battery = 0-037 Ampere. 



Reader at circle, J. P. 



Reader at galvanometer, F. W. V. 



Arc managed by A. 



Objects determination with the great arc of the deviation in a 

 rock-salt prism corresponding to a wave-length of 5X^D 2 =2 /a, 945. 

 Spectrum thrown east. 



Deviation. 39° 21" 



39° 18' 



39° 15' 



39° 12' 



First series 1 1-3) 3-3) 



[ 1-3 U-4 

 1:3 ) 3-4 ) 



5-5 ) 

 5*4) 



2-3 ) 



U-9 

 3-4 ) 



Second series —10) 0*6) 



U0-9 U-1 

 -0-8 \ 1-6 ) 



7-5) 



6-3 ) 





Spectrum thrown west. 





Third series 1*0) 



U-7 



1 0:4 ) 



2-1) 



[2-4: 



2-7 ) 



4-1 ) 0-2 ) 



U-o U-i 



3-9) -0-1 ) 



Fourth series 1 — 0*1 ) 



2-3) 



U*4 

 2-4 ) 



3.4) _o-l ) 



[o-i 



0-2 ) 



J.3-5 

 3-6) 



0-3) 



