S. P. Langley—Selective Absorption of Solar Energy. 185 
Very early the obeerynnen with this efficient RODATNAE (the 
daily, whenever o puiebe hat eve vy E portion of the curves 
here given, to the smallest infetion, been observed — 
three to twenty times, and the accidental variations due 
momentary paneer of solar toh by invisible clouds sis 
been, it is hop arly eliminated. 
The bolometric pier represented by the preceding 51 days’ 
observations, may be here regarded as being divided into two 
classes having distinct ihonile related objects. 
ee To determine the general selective absorption of = 
earth’s atmosphere throughout the entire spectrum in conn 
v 
whole forming a “series,” and these ‘‘series” are observed at 
least twice daily: namely, at meridian, and when the air mass 
is approximately double that at meridian; or else three times 
daily—at meridian, when the mass of air traversed is approxi- 
mately 14 times that at meridian, and again when it is approxi- 
mately 14x14=24 times that at meridian. 
It will be observed by reference to the map, that the points 
chosen for measurement coincide, as a rule, with the summits 
of the energy-curve, but separate investigations are still in 
* Nevertheless, as the thread, however Pracsiicih is not absolutely linear, it feels 
the cad before its center coincides with the center of the line. om interruptions 
of the energy curve are thus in fact all ina slight + degree too wide, especially at 
the Sianhasseniels of pts depression, a and it is yom that the aaa we have 
args: are really due to an aggregation of finer line 
Am. Jour. — SERIES, Wee. XXV, No. ve —Marcoxn, 18383. 
