384 ANNUAL OP SCIENTIFIC DISCOVERY. 



being to cause a sudden glance of light analogous to that we may see 

 in micaceous rocks. 



It has been observed by De la Rue that the high grounds of the 

 moon's southern hemisphere are more easily photographed than the 

 low lands of the northern hemisphere. The so-called lunar seas are 

 certainly optically as well as chemically fainter than the rest of the 

 surface, and the more rugged and mountainous regions are brighter 

 to the eye just as they are chemically brighter. If the moon were 

 polished perfectly smooth, we should not see its limb at all, but only 

 an image of the sun formed at a virtual focus by reflection from its 

 surface : the visibility of its outline, then, is entirely due to its as- 

 perities. 



Mr. Bond inclines to the opinion that we have never obtained a 

 view of the solid nucleus of Jupiter ; the planet is probably envel- 

 oped in a dense mantle of clouds, the luminosity of which may possi- 

 bly explain its apparent excess of brightness. In our own atmosphere 

 the luminosity of clouds is a well-established fact ; and our brilliant 

 auroral exhibitions are also unquestionable evidence that the earth 

 itself shines with a certain amount of native light ; it is, therefore, not 

 unreasonable to infer a similar property in Jupiter. 



SOLAR ECLIPSE OP I860. 



The following is an account of the great Solar eclipse of 1860, 

 given to the British Association, at its last meeting, by request, by 

 Professor Airy, Astronomer Royal of Great Britain. 



He proposed, he said, to commence with a few remarks upon eclip- 

 ses generally, and he should then state certain observations made in 

 the year 1842 for the first time, and continued up to the present 

 time, and should endeavor to point out the deduction which he 

 thought might legitimately be inferred from them. When first man- 

 kind began to observe total eclipses, there was no great difficulty in 

 conceiving that eclipses of the sun were caused by the interposition 

 of the moon ; but in a very short time it became obvious that this 

 interposition, which prevented the light from coming to us, was not 

 the interposition of a body at the same distance as the luminous body, 

 but that the circumstance of an eclipse must depend upon other cir- 

 cumstances, namely, the distance of the moon as related to the dis- 

 tance of the sun, and the direction in which the moon was seen as 

 related to the direction in which the sun was seen, by means of the 

 orrery. Professor Airy rendered this plainer by explaining the rel- 

 ative motions of the earth, sun, and moon, and showing the reasons 

 why some eclipses were merely partial, and others annular. 



There was a recurrence, he said, in eclipses of a very singular na- 

 ture, which had been known from the most distant period of time, 

 namely, at the termination of two hundred and twenty-three luna- 

 tions, which would occupy eighteen years fifteen days and eight 

 hours. When this period had elapsed, there was an eclipse in all 

 its important circumstances similar to the first eclipse, but in conse- 

 quence of the time required being eight hours, as well as eighteen 

 years fifteen days, the same side of the earth would not be presented 



