S. P. Langley—New method in Solar Spectrum Analysis. 148 
they meet, at the outer surface, and these owing to the excel- 
lent workmanship, still close so as to admit no light when held 
Up against thé sun. Over this slit, with their bases. almost in- 
no more in the spectrum than a particle of dust, and in. fact, 
the division between the two spectra is with difficulty distin- 
diameter.” Over them is a hood, carrying a screen, which 
recelves the image projected by the equatorial telescope. This 
image is nearly one and three-quarters inches in diameter, 
optical condition, as far as possible, similar, except as they may 
differ at their origin in the sun itself. It shows the difficulties 
of the method of research successfully employed by Mr. Huggins, 
and at Greenwich, that when the instrument is turned directly 
on the sun (i. e. so that each spectrum receives light from all 
parts of the sun’s disc), the-two sets of spectral lines will not 
ordinarily be continuous. Theoretically they should be, prac- 
Heally, we find they are not, owing to numerous latent causes 
