201 



munication had been received by him in acknowledgment of a 

 donation of coins which he had made to the Society; where- 

 upon, on motion, it was resolved that a duplicate of the usual 

 letter of thanks be transmitted by the Secretaries to Mr. 

 Brown. 



The Committee, consisting of Dr. Patterson, Prof. Bache, 

 and Prof. Park, to whom was referred the paper of Prof. Ken- 

 dall, entitled " Observations on Encke's Comet," &c, reported 

 in favour of its publication in the Society's Transactions; and 

 the publication was ordered accordingly. 



Mr. S. C. Walker communicated to the Society the follow- 

 ing- extract from a letter of Prof. S. Alexander, dated Prince- 

 ton, N. J., July 14th, 1842, containing the Professor's theory 

 for explaining the remarkable appearance presented by total 

 and annular eclipses of the sun. Prof. A. had taken this early 

 opportunity of laying his views before the Society on a subject 

 which will doubtless cause much speculation in Europe, owing 

 to the occurrence of the remarkable total eclipse of the 7th in- 

 stant. Prof. A. intended, at some future meeting, to exhibit 

 his reasons in full for the conclusions here announced. 



1. If the moon be surrounded by any substance, which can with 

 propriety be termed an atmosphere, the limit of its sensible action 

 upon light will be reduced, in consequence of a permanent terrestrial 

 and anti-terrestrial tide, which will be subject to moderate oscillations 

 of about the same extent with the moon's librations; which tide, how- 

 ever, will preserve a continual accumulation of atmosphere near the 

 point which seems to be the centre of the moon's disc, and that which 

 is diametrically opposite. The elevation of the zone of atmosphere 

 which, in such case, would surround the edge of the disc, must, in con- 

 sequence, be invariably less than that of almost any other portion. 

 The force of the earth's gravity, tending to produce a tide at the 

 moon's surface, would be more than twenty times as great as that of 

 the moon at the earth's surface, and owing to the feeble gi-avitation of 

 the moon at her own surface, the same force there would raise a tide 

 some six times as high as at the earth's surface. So that an atmos- 

 phere similar to ours would have a tide from the action of the earth 

 about 158 times as high as our atmospheric tides from the action of 

 the moon. 



2. Whatever be the constitution of the substance or substances at 



