146 SP. Langley—New method in Solar Spectrum Analysis. 
constantly so arranged each experiment, that I remained in in- 
tentional ignorance as to which spectrum came from the eastern, 
and which from the western limb, until I had determined the 
point by the different behavior of these solar and terrestrial lines, 
which I have been able to do thus far correctly in every instance. 
I believe, in fact, that the effect under proper conditions 1s so 
marked that the observer hereafter need not take pains to 
Useful tests of the desired condition are the duplication of 
such lines as 1529 of Kirchoff’s scale, and the more celebrates 
“1474.” known as a close double since Professor Youngs 
used have been principally those of the Allegheny Observatory, 
to which institution my services belong, I should have been 
Allegheny Observatory, April 14, 1877. 
