338 ANNUAL OF SCIENTIFIC DISCOVERY. 



solar system, and they are constantly entering the atmosphere of 

 our earth as meteors, the heat and light being caused by the enor- 

 mous friction of the stones against tlie air. Toward the centre of 

 attraction of the system — that is to say, the sun — these bodies 

 must be much more numerous, and if we were only certain that 

 a great mass of stones and rocks were constantly striking the sur- 

 face of the sun, it can be mathematically proved that this cause is 

 sufficient to produce these effects of intense light and heat which 

 we see. The intense light of the sun, and the smallness of the 

 hypothetical stones, make telescopic observation of no use in solv- 

 ing this problem, though on one occasion, as two observers were 

 looking at a sun-spot, they saw a brilliant body pass across it, and 

 at the same instant the magnetographic needles at Kew Observa- 

 tory were violently deflected. The zodiacal light appears to con- 

 sist of an intinity of small solid bodies revolving round the sun, 

 because the light is l^righter at one time than at another, just at 

 that anffle where it should grow brighter if its light came from 

 the sun by reflection. When the planet Venus is at the self-same 

 angle between the sun and the earth, it is also brighter, for the 

 very same reason. Now, the fact just ascertained in India sup- 

 ports the above views, towards which philosophers are at present 

 inclined to lean, because it would be difficult to suppose that enor- 

 mous solid protuberances could be present where such violent ac- 

 tion is going on, and w^here all chemical substances are probably 

 in a state of gas and fusion. 



Hansen's theory of the physical constitution of the 



MOON. 



Prof. S. Newcomb read a paper on this subject at the 1868 

 meeting of the American Association, designed to show that as- 

 tronomer's celebrated theory, that the centre of gravity and the 

 centre of figure of the moon do not coincide, to be erroneous. 



According to Hansen the moon is lap-sided, her centre of gravity 

 being some 35 miles more distant from us than her centre of 

 figure. Consequently^ though there was no atmosphere on this 

 side of the moon, there might be on the other side, and specula- 

 tors eagerly seized upon the theory to show that plants and ani- 

 mals might occupy that invisible region. He argued that the 

 whole result flowed from an oversight in Hansen's reasonino', and 

 that the whole doctrine was totally devoid of logical foundation. 

 There is not the slightest reason for supposing that the moon, in 

 this respect, differs from the other heavenly bodies in being per- 

 fectly symmetrical with respect to her centre of gravity. 



The circumstance from which it is concluded is, that the per- 

 turbations of the moon, derived from measurement, are slightly 

 greater than those deduced from the theory of gravitation. The 

 moon revolves on her axis with a uniform motion, so that if she 

 revolved around the earth uniforml}' she would always present 

 accurately the same face to us. But owing to the inequality of 



