188 W. Harkness— Observations on Comet b, 1881, 
Fraunhofer lines in the continuous spectrum of the nucleus, 
and if this really is the case its light must be at least partly de- 
rived from the sun, and should show traces of polarization. As 
just stated, I failed to discern any with the double image prism ; 
but that is not a very delicate test, although, owing to the small 
size of the nucleus, it is almost the only one practicable. Un- 
der the magnifying power used the coma filled the field of 
view with bright light, and yet exhibited not a trace of polari- 
zation when tried by that most delicate of all tests, the Savart 
polariscope; thus apparently confirming the testimony of the 
' spectroscope that the coma is self-luminous. 
On the evenings of June 28th, and July 1st and 2d, I exam- 
ined the spectrum of the comet with a spectroscope having a 
single sixty-degree prism through which a beam of light 0°82 
of an inch in diameter is passed. The wave-lengths of the 
bands in the comet’s spectrum were determined by measuring 
the interval between them and the D line given by the flame of 
a spirit lamp with a salted wick held before the object glass of 
the telescope to which the spectroscope was attached; the 
measurement being effected by a micrometer which showed a 
bright point in the field of view. Owing to the unfavorable 
position of the comet, the only telescope upon which the spec- 
troscope could be used was my three inch of 48°6 inches focus, 
which is mounted upon a portable tripod stand, but is destitute 
of clamp and tangent screws. 
Notwithstanding the brightness of the comet, it gave a spec- 
trum very ill-defined, and difficult to measure. e spectrum 
of the nucleus seemed to be continuous, and its approximate 
extent was from D to G. I did not detect any Fraunhofer 
lines in it, but possibly they may exist and yet have been 
obliterated by the rather wide opening of the slit, which was 
00125 of an inch. With a narrower slit it was difficult to 
keep the comet in the field of the spectroscope. The coma 
gave a spectrum consisting of three bright bands, so ill-defined 
that no precise measures of the wave-lengths of their edges 
could be made, but the wave-lengths of their brightest parts 
were respectively, 549°8, 512°4 and 467-2. This seems to be 
the ordinary comet spectrum. e measurement of the wave- 
length of the middle band is tolerably accurate, but the 
measurements of the other two are liable to considerable uncer- 
tainty, owing to the faintness of the bands. I estimated their 
relative brightness to be 5, 30 and 1. On July 1st a slight 
haziness of the atmosphere sufficed to render the third band in- 
visible. At a short distance from the head of the comet this 
band always faded out, and the spectrum of the tail seemed to 
consist of the first and second bands only—that is 549°3 and 
“4. 
