82 Rev, Mr, Emmeit on a curious Phanomenon [Aug. 



elliptical cavities, which are visible in almost every part of 

 the moon. 



April l?**, 9''. Scarcely a trace of the nebulous matter. 

 Powers 70, 130, 200 ; all which were used in the last obser- 

 vation. 



May 11, 12, 13, 15 ; June 9, 10. The three spots distinctly 

 visible ; but no trace of the nebulous matter ; powers, 130, 

 200, 400, 800. Appearances the same on all tlie above-men- 

 tioned days, with an aerial refractor of 18 feet ; powers 60 and 

 200. The general appearance is represented in ouUine in the 

 figure, in which a represents Alopecia; ^theN spot in Russell's 

 maps, but not noticed by Hevelius or Cassini; c the spot which 

 is the subject of this paper, surrounded with the nebulosity. 

 The nebulous appearance here spoken of is not to be confounded 

 with a darkish shade which is always to be seen near the same 

 part of Ma&otis, and which was distinctly visible at the same 

 time : the nebulosity in question was very much blacker ; it 

 was so conspicuous as to strikis the eye immediately. On the 

 12th April it was so intense that the spot c could not be very 

 readily discerned. It was a more conspicuous object than any 

 spot m Moeotis, and therefore it has not been permanently 

 visible ; had it been so, it is almost impossible that Hevelius, 

 Cassini, and Russell, who have noticed far less conspicuous 

 objects, within a few seconds of it, should all have omitted it; 

 and this part of the moon being one which during several years, 

 for reasons which will appear when a sufficient series of obser- 

 vations shall have been made, I have examined very minutely, I 

 can positively state, that the nebulous appearance never pre- 

 sented itself, in any of the numerous observations I have made, 

 from the year 1814 to the present time. Respecting the spot c 

 from which the nebulosity seemed to issue which is now visible, 

 I cannot speak so positively. It is not noticed by Hevelius, 

 Cassini, or Kussell ; and it is well known that the latter devoted 

 nearly 30 years to making his maps ; that he used the best 

 instruments ; and that he has carefully delineated almost every 

 visible speck. 1 do- not recollect to have seen it previously to 

 the 12th of April. 



I regret that 1 had no scientific friend with me whose testi- 

 mony might give additional weight to this account of the 

 observation of the 12th April ; however, I hope that some other 

 astronomers ibay have been fortunate enough to see the phseno- 

 menon. I should have communicated the inteUigence at an 

 earlier period, had it not been requisite to observe the moon at 

 about tne same age afterwards: this has been done during two 

 successive lunations. 



It is scarcely safe to hazard a conjecture respecting the cause 

 of this phsenomenon : I shall, therefore, merely propose a query. 

 Was it the smoke of a volcano? or was it cloudy matter? The 



