Measurements in the Extreme Infra-red Spectrum. 



Series a.. 

 a-h = 360 

 b -i = 36-0 



773 



Series (3. 

 a -h =36*2 



b-i =36-0 



a'-tf = 35-7 

 b'-i' = 35-8 



A = 35-9 

 . _359 

 Al -TT 

 35'9 

 1(5 



X,= 



. 20-91 = 53-6 /^. 

 .20 91 = 46-9/*. 



$2 



a'-A'= 36*0 

 ZM' = 35-2 



A = 35-9 

 0-23 



7i = 



72 



0-20 



* 



= 0-66, 



The fact is here again emphasized that the energy- 

 distribution curve, as calculated from the above constants 

 (corresponding to fig. 8), is only an approximation. In 

 view of the high reflectivity of rock-salt for Reststrahlen 

 of sylvine *, it is most probable that the slope of the energy 

 curve toward greater wave-lengths is a more gradual one 

 than fig. 8 indicates. 



Reststrahlen of Sylvine {Potassium Chloride). 

 Three series of observations were recorded, one of which 

 was made with the wedge-shaped plates. All are in good 

 agreement. That observed under the most favourable con- 

 ditions is indicated in fig. 4 ; the numerical data follow : — 



Maxima. 



.Minima. 













w = 17 ; a -i' = 50'0 











a'-k = 50-0 



a 



201-0 



a' 



1980 



6-^=60-1 



b 



194-7 



// 



191-4 



b'-l =49-5 



c 



188*4 



<• 



185-5 



c -I' = 49-4 



d 



L82-3 



d' 



1791 



h'-r = 50-0 



e 



1762 



e' 



173-7 



i -,-' = 50-0 



f ... 



170-7 



/ 



1680 



i'-s = 50-2 



a 



1650 



g' 



1625 



k -s'= 51-0 



h 



159-6 



//' 



1570 



k'-t = 506 



i 



153-9 



i' 



1510 







k 



1480 



// 



144-6 



50-1 



/ 



141-9 



1' 



139-0 





VI 



1360 



m' 



133 6 



X,= ^. 20-91 =616 u. 



17 r 



n 



[298 



// ' 



L273 



o 



1240 



o' 



121-6 





/' 



118-8 



v 



1160 



X a =X 1 g=69-9^. 



q 



1130 



q' 



110-1 



/■ 



8 



1070 

 100-8 



r' 



s' 



1039 

 97-0 



7l =0-074, y, = 0-084. 



t 



94 



t' 



90-9 



^ =0-63. 



it 



87"2 



u' 



84-4 



V 



81-0 







ti 



H. R 



ubens anc 



IE. As 



chkinasSj 



Wied. Ann. lxv. p, 253 (1808 



