248 Prof. S. Arrhenius on the Influence of Carbonic Acid 



X=1'5/a, after which it increases rapidly to a maximum at 

 X=2'6 fi, and attains a new extraordinarily strong maximum 

 at \ = 4*6 (Langley's Y). According to Angstrom the ab- 

 sorption of carbonic acid is zero at X = 0'9 /ju, and very weak 

 at X=l*69 /jl, after which it increases continuously to \=4*6//. 

 and decreases again to \= 60//.. This behaviour is entirely 

 in agreement with the values of log x in Table II. From 

 the value zero at 40° (A, = 1*0 /a) it attains a sensible value 

 (-0*0296) at 39°'45 (X=l*4/i), and thereafter greater and 

 greater values (-0*0559 at 39°*30, and -0-1070 at 3b°-15) 

 till it reaches a considerable maximum (—0*3412 at 39°, 

 X=4*3/Lt). After this point the absorption decreases (at 

 38°-45 = 5-6^1og^=-0-2035). According to Table II. the 

 absorption of carbonic acid at 38 o, 30 and 38°*15 (\=7*t> 6. 

 and 8*7 //,) has very great values (log x= —0*2438 and 

 —0*3730), whilst according to Angstrom it should be o insensible. 

 This behaviour may be connected with the fact that Angstrom's 

 spectrum had a very small intensity for the larger wave- 

 lengths. In Paschen's curve there are traces of a continuous 

 absorption by the carbonic acid in this whole region with 

 weak maxima at X=5*2//., X=5*9 //,, \=6'6/jl (possibly due 

 to traces of water-vapour), X = 8*4 fi, and X=8'9 /ju. In 

 consequence of the strong absorption of water-vapour in this 

 region of the spectrum, the intensity of radiation was very 

 small in Langley's observations, so that the calculated ab- 

 sorption-coefficients are there not very exact (cf. above, 

 pp. 242-243). Possibly the calculated absorption of the car- 

 bonic acid may have come out too great, and that of the 

 water-vapour too small in this part (between 38°*30 and 38°*0). 

 This can happen the more easily, as in Table I. K and W 

 in general increase together because they are both propor- 

 tional to the ** air-mass." It may be pointed out that this 

 also occurs in the problems that are treated below, so that the 

 error from this cause is not of so great importance as one 

 might think at the first view. 



For angles greater than 38° (\>9*5/a) we possess no 

 direct observations of the emission or absorption of the two 

 gases. The sun's spectrum, according to Langley, exhibits 

 very great absorption-bands at about 37°*50, 37°*25, 37°, and 

 36 o, 40°. According to my calculations the aqueous vapour 

 has its greatest absorbing power in the spectrum from 38° to 

 35° at angles between 37°*15 and 37°*45 (the figures for 

 35°*45, 35 o, 30, and 35°* 15 are very uncertain, as they de- 

 pend upon very few measurements) , and the carbonic acid 

 between 36°*30 and 37°*0. This seems to indicate that the 

 first two absorption-bands are due to the action of water- 



