266 
Proceedings of the Royal Society 
2. On Bisulphide of Carbon Prisms. By Dr Daniel Draper. 
Communicated by Professor Piazzi Smyth. 
New York Meteorological Observatory, 
May Zlth, 1885. 
C. Piazzi Smyth, 
Astronomer Royal of Scotland. 
Dear Sir, — I take pleasure in answering your kind note of May 
9th, in regard to the experiments made by my brother Dr Iienry 
Draper, on bisulphide of carbon prisms. 
In this letter I shall only refer to those portions of my brother’s 
experiments, which did not appear in sufficient detail in the paper 
published in the American Journal of Science , by Professor George 
F. Barker of the University of Pennsylvania. 
My brother was led to perform these experiments with bisulphide 
of carbon prisms, with the stirrer, and uniform temperature bar, on 
account of the trouble he had experienced while working upon 
“ Oxygen in the Sun ” in his old laboratory, in getting coincidences 
between the solar spectrum, and the spectra of various other sub- 
stances with the electric spark. He found that sometimes the lines 
of the overlapping spectra would coincide, and at other times there 
would be discrepancies, although the experiments appeared to have 
been made in exactly the same manner each time. 
On continuing these experiments on oxygen in his new laboratory 
he found that the discrepancies were much greater than before. 
This led him to suspect that the lack of coincidence was due to 
temperature. 
At about this time Mr Lewis M. Rutherfurd told my brother of 
his experience, in shaking the bisulphide of carbon prisms just before 
using them, and the surprising results they gave, and also the short 
time of their continuance to give good results. 
My brother and I, in talking this subject over, decided to see if 
some simple plan could not be devised to keep the fluid in the 
prism continually stirred, or shaken by some small steady motor 
power. To try this device brother Henry borrowed from our 
brother-in-law, Dr Mytton Maury, his Edison electric pen, which 
consists of a very small magneto-electric engine, mounted on the 
upper end of a (stylus) or light tube, through which a needle point 
