414 Mr. W. Huggins and Dr. W. A. Miller on the 



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 spectrum-apparatus. The quan- 

 tity of light from different parts was observed to be very differ- 

 ent ; 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 consider- 

 able lunar atmosphere f- 



9. The Planets Jupiter, Saturn, Mars, and Venus. — The very 

 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 



* [With the spectrum-apparatus described at page 415, 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 ¥ <^ inch X -^oo inch. The image of 

 the moon formed by the object-glass of the telescope has a diameter of J '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 ascer- 

 tained by means of the finder attached to the telescope. For 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 cy- 

 lindrical 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 cir- 

 cumstance 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.] 



The authors observed the partial eclipse of the moon on October 4, 1865. 

 The spectrum of the penumbra appeared singularly shortened at its more 

 refrangible end. The atmospheric groups near D were distinctly seen in 

 the light of the penumbra. 



One of the authors observed the disappearance of the spectrum of 

 e Piscium at its occultation on January 4, 1866. No dark lines additional 

 to those belonging to the star were seen as the moon's dark limb approached 

 and occulted the star. The disappearance of the spectrum was not pre- 

 ceded by any sensible failure of the blue or red rays, but the spectrum ap- 

 peared to remain unaltered in the relative intensity of its different parts up 

 to the moment of extinction. (Monthly Notices of the Royal Astronomical 

 Society, vol. xxv. p. 60.)] 



