Mercurial Atmosphere. — New Comet. 151 



MERCURIAL ATMOSPHERE. 



Mr. Faraday states (in the Quarterly Journal of Science) that 

 a small piece of leaf-gold attached to the under part of the 

 stopper of a bottle, the bottom of which was covered, about an 

 eighth of an inch deep, with mercury, having been set aside in a 

 dark and cool place for six or eight weeks, was found at the end 

 of that time whitened by the mercury. This experiment has 

 been repeated several times, care being taken that mercury 

 should not get to the gold, but by passing through the air in the 

 bottle, and always with the same result. It has long been ad- 

 mitted, that in the upper part of the barometer and thermome- 

 ter there is an atmosphere of mercury, even in common tem- 

 perature ; and now it is proved that even in the air mercury is 

 always surrounded by an atmosphere of the same substance. 



NEW COMET. 



We announced in our last, that a new comet had been seen 

 at the Royal Observatory, Paris, on the 21st of December. We 

 now learn that the same comet was discovered on the same 

 night about seven o'clock by Signer Pons, astronomer of the 

 Duchy of Lucca. It appears like a white spot, not thick nor of 

 a kernel form, and with a very small tail. On the 2"2d, Signer 

 Pons continued his observations, and perceived that the comet 

 had not changed its position, but that its tail was becoming more 

 visible, and its light had acquired greater intensity. He thence 

 concluded that this comet will become rapidly more luminous, 

 and to such a degree as to be visible by the naked eye. Astro- 

 nomers have fixed its right ascension at deg. 30 niin., and its 

 northern declination at 18 deg. between the stars of the sixth 

 magnitude ^ and u of Pegasus. 



ASTRONOMY. 



Sir, — I have been very anxious to meet with a variety of good 

 observations of the late solar eclipse, in order to determine the 

 error of the lunar tables. From the observations of Mr. Evaiis, 

 inserted in your Number for December, it appears that the ta- 

 bles of M. Burckhardt came nearer the truth, on this occasion, 

 than those of M. Burg. 



In calculating the elements from both these tables, I found 

 the greatest differences in the moon's semidiamcter and hori- 

 zontal parallax. These two elements, taken from Burckhardt, 

 unite in making the instant of commcncemei:t later than it comes 

 out by Burg's tables ; but, for the end, their eflfccts nearly coun- 

 terbalance one another, so that the instant of last contact comes 



out 



