468 MR. A. FOWLER ON THE SPECTRUM OF MAGNESIUM HYDRIDE. 



ordinary solar spectrum is for several reasons inconclusive, but there is evidence that 

 very few, if any, of the thousands of faint lines tabulated by BOWLAND are to be 

 accounted for by this substance. 



In concluding this paper, I am anxious to express my indebtedness to those who 

 have rendered assistance in a somewhat laborious investigation. Mr. H. SHAW, 

 A.B.C.S., has made many of the calculations for checking my determinations of 

 wave-lengths, and Mr. A. EAGLE, B.Sc., has been especially helpful in the experi- 

 mental part of the work, which he has carried out with great skill. Valuable 

 assistance was also given by Mr. T. BA.NFIELD in preparing the photographs for 

 reproduction. 



Description of Table of Wave-lengths. 



The wave-lengths are expressed as nearly as possible on the scale of BOWLAND'S 

 " Preliminary Table' of Solar Spectrum Wave-lengths." They may be reconverted 

 to the "absolute" scale of FABRY and BUISSON, on which they were originally 

 calculated, by subtracting 0*22 from 5621 to 5365*1 inclusive, and 0*170 from 53651 

 to 4371. 



In the column headed " Int." (intensity), the brightest lines are represented by 10 

 and the fainter lines by numbers ranging down to 1, while the faintest lines, as in 

 BOWLAND'S tables, are denoted by 0, 00, and 000. The letter " n," following the 

 intensity number, indicates that the line is unusually nebulous or diffuse, while " s" 

 indicates that the line is of more than average sharpness ; d ? indicates that the line 

 is probably double, though not clearly measurable as such. Some of the lines marked 

 " 11 " may possibly also be double. 



In the table referring to the green band, the letters a, /3, &c., indicate the lines 

 which are probably associated in the respective series. 



It should be noted that some of the magnesium hydride lines may be masked by 

 the ordinary arc and spark lines of the metal magnesium which appear on the plates 

 from which the wave-lengths were determined, namely: the arc lines 5528*641, 

 5183791, 5172*856, 5167*497, 4703*177, 4571*275, and the enhanced line 4481*31. 



YELLOW-GREEN FLUTING. 



