in the Air upon the Temperature of the Ground. 247 



strong absorption-bands in this interval, among which those 

 marked p, c, t, and (f> are the most prominent*, and these 

 absorption-bands belong most probably to the aqueous vapour, 

 That Paschen has not observed any emission by water-vapour 

 in this interval may very well be accounted for by the fact 

 that his heat-spectrum had a very small intensity for these 

 short- waved rays. But it may be conceded that the absorption- 

 coefficient for aqueous vapour at this angle in Table II. is 

 not very accurate (probably too great), in consequence of the 

 little importance that Langley attached to the corresponding 

 observations. After this occurs in Langley's spectrum the 

 great absorption-band ty at the angle 39*45 (\=1*4 /a), where 

 in Paschen 's curve the emission first becomes sensible 

 (log y=. — 0" 1105 in Table II.). At wave-lengths of greater 

 value we find according to Paschen strong absorption-bands 

 at \ = 1*83^ (H in Langley's spectrum), i.e. in the neigh- 

 bourhood of 39°*30 and at \ = 2'64/x (Langley's X) a little above 

 the angle 39°' 15. In accordance with this I have found 

 rather large absorption-coefficients for aqueous vapour at 

 these angles (log?/ = - 0'0952 and —0-0862 resp.). From 

 X=3*0 \a, to X = 4*7yLt thereafter, according to Paschen the 

 absorption is very small, in agreement with my calculation 

 (logy = —0*0068 at 39°, corresponding to X = 4*3/a). From 

 this point the absorption increases again and presents new 

 maxima at A,= 5*5/i>, X=6*6 /u,, and \=7'7 fi, i.e. in the 

 vicinity of the angles 38°*45 (\ = 5'G fi) and 38°*30 (X=7 1/x). 

 In this region the absorption of the water-vapour is con- 

 tinuous over the whole interval, in consequence of which the 

 great absorption-coefficient in this part (log y— — 0'3114 and 

 — 0*2362) becomes intelligible. In consequence of the de- 

 creasing intensity of the emission-spectrum of aqueous vapour 

 in Paschen's curve we cannot pursue the details of it closely, 

 but it seems as if the emission of the water-vapour would also 

 be considerable at X = 8"7//, (39 c *15) ? which corresponds with 

 the great absorption-coefficient (log y= —0*1933) at this 

 place. The observations of Paschen are not extended farther, 

 ending at \=9*5yu,, which corresponds to an angle of 39°*08. 

 For carbonic acid we find at first the value zero at 40°, in 

 agreement with the figures of Paschen and Angstrom f. The 

 absorption of carbonic acid first assumes a sensible value at 



* Langley, Ann. Ch. et PJiys. ser. 6, t, xvii. pp. 323 and 326, 1889, 

 Prof. Papers, No. 15, plate 12. Lamansky attributed his absorption-bands, 

 which probably had this place, to the absorbing power of aqueous vapour 

 (Pogg. Ann. cxlvi. p. 200, 1872). 



t It must be remembered that at this point the spectrum of Paschen 

 was very weak, so that the coincidence with his figure, may be accidental, 



