Wave-lengths in the Invisible Prismatic Spectrum. 209 



sures, where the wave-lengths of cold lines are given with most 

 accuracy. Of these it is just to distinguish those by Abney 

 as possessing a degree of exactness before unknown. There 

 are some doubts about the band at F"35 having really been 

 observed before, but I have included this among those whose 

 existence was known or suspected before my measures. 



The values here given were obtained by me in 1882, and 

 first published in the Comptes Rendus of the Institute of 

 France, for September 11, 1882, in the form of charts, which 

 were drawn from them. These charts were so much reduced 

 by the first engraver that, though these values are still deter- 

 minable from them, it may be convenient to repeat them here 

 in their original tabular form, with the addition of the pro- 

 bable errors (Table V.). 



Lines known to previous Investigators. 



(0*815). Near the utmost limit of visibility. Appears to 

 coincide with Capt. Abney's Z and Draper's a. 



(0*85). Apparently agrees with Abney's 8540. 



(0*89). An inconspicuous line. Abney has a heavy line 

 near here. Possibly corresponds to Draper's /3. 



(0*91). Inconspicuous; possibly a part of Draper's 13. 



(0*94). Very heavy line ; marks the extreme limit of 

 Draper's investigations, according to his own statement, and 

 seems to be identifiable with the last definite gap in La- 

 mansky's curve. (Allegheny observations make it probably 

 telluric.) 



(1*12). Still colder than preceding. The gap represented 

 bv this line was taken by Lamansky for the end of the 

 spectrum. (Allegheny observations make it probably of tel- 

 luric origin.) 



(1*26). Inconspicuous line. 



(l*35- # 37). Very remarkable band. Almost absolutely cold 

 and black. So broad and diffuse that it is difficult to mark 

 its limits, but coldest part seems to have a wave-length of 

 1*36 and 1'37. (Allegheny observations make it probably of 

 telluric origin.) Possibly the "-v/r" of Abney's chart. It 

 seems to be the extremest limit of previous investigations. 



Newly-discovered Lines and Cold Bands. 



(1*55 and 1*59). Inconspicuous lines. 



(r81-l'87). Great cold band, first discovered on Mount 

 Whitney. Probably of telluric origin. It is not the furthest 

 Phil. Mag. S. 5. Vol. 1 7. No. 105. March 1884. P 



