178 S. P. Langley on the Selective Absorption of Solar Energy. 



nishes continuously as the wave-length increases (save for the 

 interruptions already cited) to the extremity of our charts. 



The graphic representation of this and other extratelluric 

 curves of energy will be given in a later memoir, in such a 

 form as to show from the mean of a year's observations the 

 percentage of absorption suffered by each ray in the entire 

 spectrum, visible and invisible. 



The reader who may desire still fuller details as to the appa- 

 ratus, the original observations, and their treatment, is referred 

 to the forthcoming official publication already mentioned. In 

 the later memoir will be found a description of the method 

 used for determining the wave-lengths corresponding to mea- 

 sured deviations, and the formulas for deducing from the 

 prismatic spectrum the distribution of the energy and the 

 extent of the spectrum on the normal scale. 



Summary. 



As one result of this present research, the chart of the pris- 

 matic spectrum as observed at Allegheny with the bolometer 

 is now presented (Plate III.). The abscissae are proportional 

 to deviations, and the ordinates to measured energies. The 

 second chart now given (Plate III.) represents the normal 

 spectrum as deduced from the prismatic; as it has been thought 

 advisable to present it here for the reader's convenience, in 

 advance of a description of the means used for making it. 

 The abscissas on this are proportional to actually measured 

 wave-lengths, and the ordinates to measured energies. In 

 both charts the area between ordinates corresponding to like 

 wave-lengths is the same; and hence the total areas are the 

 same. Their very dissimilar contour is due to the prismatic 

 distortion. 



Faint indications of solar energy below the lowest point 

 here shown have been found; and these, with some considera- 

 tions as to the nature of the new absorption-bands, may be 

 given hereafter, together with tables (already prepared) of the 

 absorptive action of the solar atmosphere for each spectral ray. 

 These will, it is hoped, give with a satisfactory approximation 

 the distribution of the energy before any absorption whatever 

 at the source — that is, of the energy in the photosphere itself. 



The extent of the newly observed region may be most 

 clearly seen by reference to the map of the normal or diffrac- 

 tion-spectrum (Plate III.). Previous maps end at or near 

 wave-length 1^*2. Beyond this point (with the exception of 

 the single band near wave-length ]/**4) every line, and 

 every ordinate representing heat, is believed to be new. The 

 extent of the region here newly mapped is then considerably 



