420 
MR. W. HUGGINS AND DR. W. A. MILLER ON 
December 31, 1863, March 15 and 19, and April 12, 1864. The solar lines were per- 
fectly well seen, appearing exceedingly sharp and fine. The line D was well divided, 
and its components were observed to coincide with those of sodium. Coincidence of 
the magnesium group with the three lines forming b was also observed. The lunar 
spectrum is indeed full of fine lines, and they were well seen from B to about halfway 
between G and H. On all these occasions no other strong lines were observed than 
those which are visible in the solar spectrum when the sun has a considerable altitude. 
Previously to the observations of March 15 and 19 and April 12, 1864, the appa- 
ratus was directed to the sun when near the horizon, and the relative positions and 
characteristic appearances of the atmospheric lines in the orange and red were carefully 
observed. These portions of the spectrum were closely scrutinized when the moon’s 
light was afterwards examined ; but no indication of similar lines could be detected. On 
each of the three evenings just mentioned successive portions of the moon’s illuminated 
surface from the centre to the circumference were brought before the slit of the spec- 
trum apparatus. The quantity of light from different parts was observed to be very 
different, but not the smallest change in the lines of the spectrum could be perceived, 
either in respect of relative intensity or the addition or disappearance of any lines*. 
The result of this spectrum analysis of the light reflected by the moon is wholly 
negative as to the existence of any considerable lunar atmosphere f. 
9. The Planets Venus, Mars, Jupiter, and Saturn . — The very sensible and rapidly 
changing appearances of the disk of Jupiter, other than those due to the rotation of the 
planet, present very strong evidence of the existence of a very considerable atmosphere 
about Jupiter. The same, though in a much less marked degree, is probably true of 
Saturn and Mars. In addition, the diminished brightness of the disk of Jupiter near 
the periphery supports the inference that an atmosphere exists about that planet. 
The planet Jupiter was observed on April 12, 1862, and April 14 and May 1, 1863. 
* [With, the spectrum apparatus described at page 421, the spectra of particular and very limited regions of 
the moon’s surface can be examined. The opening of the slit of the apparatus corresponding to a spectrum that 
can be separately observed is about gyy inch x inch. The image of the moon formed by the object-glass 
of the telescope has a diameter of 1-04 inch. Practically it is found that the light reflected from an area upon 
the surface of the moon of about one-third that of Tycho can be analyzed in the instrument. 
The particular spot of the moon’s surface under observation can be ascertained by means of the finder attached 
to the telescope. Eor this purpose, however, a special set of wires, accurately adjusted, and an eyepiece of 
considerable power are necessary. When the part of the moon’s surface under observation presents marked 
inequalities of illumination, the spectra of these differently illuminated portions can be easily recognized by the 
differences in their comparative brightness. In these observations the cylindrical lens may be removed. — 
August 31, 1864.] 
f [A remarkably favourable opportunity of observing the effect upon the solar spectrum of transmission 
through a very large extent of the earth’s atmosphere presents itself on the occasion of an eclipse of the moon. 
We had made preparations to observe the copper-coloured light reflected from the moon during the eclipse of 
June 1, 1863. The small altitude of the moon on this occasion rendered the observation impossible, from the 
circumstance that the eye end of the telescope, increased in length by the spectrum apparatus, came too near 
the wall of the observatory. — August 31, 1864.] 
