80 The Spectroscope in Mint Assaying. January, 
desirable. With the view of probing for new fa¢ts in this 
direction, a limited but promising field of experiment has 
lately been adopted simultaneously, but independently, in 
the assay departments of the Royal Mint in England, and 
of the U.S. Mint at Philadelphia, and the attempt has 
been made to insert the wedge of future investigation by 
obtaining from the spectroscope a quantitative analysis of 
the composition of metallic alloys. 
In a late annual report of the Royal Mint, Mr. Wm. 
Chandler Roberts, the chemist of the Mint (who with 
Mr. J. Norman Lockyer, the pioneer in spectroscopic re- 
search, has been conduéting a series of experiments), states 
he is satisfied that by means of the spectroscope very minute 
differences in composition of gold-copper alloys can be as- 
tained. He, however, ‘“‘ refrains from describing the process, 
as the exact method of manipulation had not been deter- 
mined upon. In the following paper, which also appears in 
No. xcvili. of the ‘‘ Journal of the Franklin Institute,” the 
attempt is made to narrate, not technically, the process 
adopted, and the conclusion arrived at, in the experiments 
made in Philadelphia, the details of which are contained in 
a report by the writer to the chief assayer of the Mint, 
dated May, 1874, and published in the “‘ Proceedings of the 
American Philosophical Society” of the 15th of that month, 
vol. xiv., page 162. 
The beautiful parti-coloured band of light, resembling a 
section of a miniature rainbow, resulting from the passage 
of a ray of white light through a prism, is familiar to every 
one; this simple experiment forms an appropriate introduc- 
tion to the fascinating study of spectrum analysis. 
Every kind of light not stri€tly mono-chromatic may, by 
means of the prism, be resolved into its component colours. 
The speCtroscope is a simple combination of prisms and 
lenses for the scientific examination of these different colours 
or spectra. 
The numerous terrestrial elements, when in the state of 
incandescent vapour, give their own distin¢tive colours, 
which appear in the spectroscope as lines of light arranged 
in definite positions, whereby each element may be easily 
recognised. 
The passage of powerful ele¢tric sparks (from an indu¢tion 
coil) between two terminal points of the metal to be ex- 
examined, vaporises a small portion of the metal, and this 
incandescent vapour transmits to the eye of the spectroscopic 
observer its luminous autograph which nature never counter- 
feits. Should either or both of the metallic points, or elec- 
