40 REPORT — 1878. 



into this column wherever it appeared that the interpolation could be inr.de with 

 sufficient safety. The wave-lengths of this list are wave-lengths in air of 700 millims. 

 pressure at Upsala and 10° C. temperature. 



Column 3 contains the reciprocals of the numbers in column 2, each multiplied by 10". 

 Each number in this column may accordingly be regarded either as the number of 

 times that the corresponding wave-length-in-air goes into one millimetre, or as the 

 number of complete oscillations in the time fir, where ft is the index of refraction 

 of air for that ray. 



Column 4 contains the correction for the dispersion of air of 760 millims. pressure and 

 16° temperature, deduced from Ketteler's observations. (See ' Philosophical Maga- 

 zine ' for 1866, vol. ii. p. 336.) 



Column 5 gives the oscillation-frequency of each ray in the time r, the time that light 

 takes to advance one millimetre in vacuo. Or the numbers of this column may be 

 regarded as the numbers of waves per millimetre in vacuo. 



Column 6 indicates the intensity and width of each ray between A and G, as determined 

 by Kirehhoff, and between G and H 2 , as determined by Mr. Burton, 6 being the 

 most intense and g being very wide, viz. about 0'15 of one degree of the scale of 

 oscillation-frequencies. 



Column 7 enumerates the substances which have been found to emit bright rays coincident 

 with dark solar rays, and contains some other remarks. 



Column 8. In the last column the rays are bracketed into the groups which strike the eye 

 in looking at the spectrum, and to each group is assigned a number winch suffi- 

 ciently indicates its position upon the standard scale. 



