160 S. P. Langley on the Selective Absorption of Solar Energy, 



atmospheric transmission, by the comparison of the noon and 

 afternoon measures. Those days on which noon measure- 

 ments were taken which were rendered useless for this purpose, 

 by subsequent changes in the condition of the sky or by other 

 causes, are indicated by an asterisk. It will be seen that of 

 twenty-nine days of observation only ten observations could 

 be fully utilized. 



Dates:— 1880, Nov. 12,* Dec. 11,* Dec. 18.* 1881, 

 Jan. 12,* Jan. 18,* Jan. 28, Feb. 2, Feb. 3,* Feb. 5,* 

 Feb. 17, Feb. 19,* Feb. 22,* Feb. 26,* March 2,* March 10,* 

 March 11,* March 25,* March 28,* April 7,* April 16,* 

 April 22, April 23, April 28% April 29, April 30, May 4,* 

 May 26,* May 27,* May 28. 



The following table gives the observed galvanometer-deflec- 

 tions reduced to a scale on which the readings are proportional 

 to the current passing through the galvanometer. 



dj = galvanometer-deflection with high sun, 

 d„= „ „ „ low sun. 



Table I. 



X= Om-375 -400 -450 -500 -600 700 -800 -900 1-000 



To„ o« 1QQ1 f*i — 101 - 374 383 320 221 144 102 

 jan.zo, io»i.., |^ _ 43 _ 167 26g 215 221 116 7g 



™ oK „ (d t 34 80 215 289 307 293 175 ... 93 



* eD '^ \d„ 3 20 61 104 141 195 91 ... 47 



t^k 17 (d, 23 62 120 232 260 227 188 ... 71 



* 60 - u \d„ 8 25 58 110 133 151 80 ... 39 



A™199 M 19 435154 236 262 2395 177'5 123-5 98 



Apm ^ [d„ 6-5 17 63 119-5 171-5 180-5 122-5 89-5 84 



Ar,ril9qAM l d > - 59 152 206 263 227 191 12 1 94 

 April ;W, A.M.... j^ _ 41 124 lg9 25g 257 lg7 122 g6 



. - 19 o „ fd, ... 59 152 206 263 277 191 121 94 

 Aprils, p.m..,. | ^ ^ 32 103 124 18g 1Q8 140 g0 6g 



j,,,,,, fd, 13 29 113 151 235 235 139 100 89 

 April ^y,A,M....|^ 1Q 22 65 126 156 197 135 93 g6 



a™19Q ™ M 13 29 113 151 235 235 139 100 89 

 Aprii-y, p.m..., K^ 5 8 49 62 107 116 72 58 66 



. ., on id, 21 55 121 186 245 259 175 119 90 



ApmdU \d„ 18 33 97 148 220 232 166 97 80 



M^9« f d i 8 34 " 109 144 134 89 64 52 



mayzo " {d„ .... 2 9 27 52 66 61 33 39 



The next table gives the sun's position, and the correspond- 

 ing air-mass for each series in the previous table. 



In this table, /3 denotes the reading of the barometer, and 



