[ 139 ] 
II. On the Spectra of some of the Chemical Elements. 
By William Huggins, Esq., F.R.A.S. Communicated by Dr. W. A. Miller, Treas. B.S. 
Received November 5, — Read December 10, 1863. 
1. I have been engaged for some time, in association with Professor W. A. Miller, in 
observing the spectra of the fixed stars. For the purpose of accurately determining the 
position of the stellar lines, and their possible coincidence with some of the bright lines 
of the terrestrial elements, I constructed an apparatus in which the spectrum of a star 
can be observed directly with any desired spectrum. To carry out this comparison, we 
found no maps of the spectra of the chemical elements that were conveniently available. 
The minutely detailed and most accurate maps and tables of Kirchhoff were confined 
to a portion of the spectrum, and to some only of the elementary bodies ; and in the 
maps of both the first and the second part of his investigations, the elements which are 
described are not all given with equal completeness in different parts of the spectrum. 
But these maps were the less available for our purpose because, since the bright lines 
of the metals are laid down relatively to the dark lines of the solar spectrum, there is 
some uncertainty in determining their position at night, and also in circumstances 
when the solar spectrum cannot be conveniently compared simultaneously with them. 
Moreover, in consequence of the difference in the dispersive power of prisms, and the 
uncertainty of their being placed exactly at the same angle relatively to the incident 
rays, tables of numbers obtained with one instrument are not alone sufficient to deter- 
mine lines from their position with any other instrument. 
It appeared to me that a standard scale of comparison such as was required, and 
which, unlike the solar spectrum, would be always at hand, is to be found in the lines of 
the spectrum of common air. Since in this spectrum about a hundred lines are visible 
in the interval between a and H, they are sufficiently numerous to become the fiducial 
points of a standard scale to which the bright lines of the elements can be referred. 
The air-spectrum has also the great advantage of being visible, together with the spectra 
of the bodies under observation, without any increased complication of apparatus. 
2. The optical part of the apparatus employed in these observations consists of a 
spectroscope of six prisms of heavy glass. The prisms were purchased of Mr. Browning, 
optician, of the Minories, and are similar in size and in quality of glass to those 
furnished by him with the Gassiot spectroscope. They all have a refracting angle 
of 45°. They increase in size from the collimator; their faces vary from 1*7 inch by 
1*7 inch to 1*7 inch by 2 inches. 
The six dispersing prisms and one reflecting prism were carefully levelled, and the 
mdccclxiv. u 
