164 Scientific Intelligence. 
precaution, which gives the appearance of extraordinary accuracy 
to the adjustment, is practically an impossibility with the appara- 
tusemployed. Minimum deviation of the D line as a whole could 
not under these circumstances be distinguished from that of either 
of its components, nor could that of D, be distinguished from that 
of D,. Moreover, it is difficult to understand why he adjusts to 
minimum deviation for D’ and not for G, near which the work 
is to be done. Instead of D’, the line for which his apparatus 
was adjusted should have been chosen in the photographic por- 
tion of the spectrum, for example between G and H. 
n page 265, line 25, the author says that this “is 
to find that in getting his oxygen spectrum, he uses only “two 
flint glass prisms of 60°” and for objectives, “ achromatics of 
ten inches focus.” The bright line spectrum of oxygen taken 
ttac W ’ 
vision battery of nine prisms and an observing telescope of forty- 
two inches focal length. The original negatives taken with the 
g spe 
ru m spectrum. The graphic method, employed to 
supplement the direct method, does not appear to help the com- 
parison, since the author nowhere gives both codrdinates to the 
curve constructed. 
ixth, it is more than questionable whether the measurements of 
upon the paper scal 
to measure to one hundredth of a scale-division would require the 
or nine apparently), required to give the wh h 
spectrum, must, unless special precaution was taken (of W ich 
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