OF SOME OF THE STAES AND NEBULAS. 
559 
My friend, Dr. William Allen Millee, visited the observatory on this evening, and 
kindly took part in the following observations. 
The general arrangement of the apparatus with which the comparison was made is 
shown in the following diagram. 
A glass bottle converted into a gas-holder, a, contained the olefiant gas. This was con- 
nected by means of a flexible tube, with a glass tube b, into which were soldered two plati- 
num wires. The part of the tube in front of the points of the wires had been cut away, 
and the surfaces carefully ground. A small plate of glass closed the opening by being held 
in its place by a band of vulcanized india-rubber. This tube was arranged in its proper 
position before the small mirror of the spectroscope c, by which the light of the spark was 
reflected into the instrument, and its spectrum was seen immediately beneath the spec- 
trum of the comet. The spectroscope employed was furnished with two prisms of 60°. 
The brightest end of the middle band of the cometic spectrum was seen to be coincident 
with the commencement of the corresponding band in the spectrum of the spark. As this 
limit of the band was well defined in both spectra, the coincidence could be satisfactorily 
observed up to the power of the spectroscope ; and may be considered to be determined 
within about the distance which separates the components of the double line D. As 
the limits of the other bands were less distinctly seen, the same amount of certainty of 
MDCCCLXVIII. 4 H v. 
