232 PHILOSOPHICAL TRANSACTIONS. [anNO 1792. 



course of lectures in 1791- In these experiments, he was assisted by Mr. Eg- 

 ginton, of Queen's College, Cambridge, who attended that course. The pro- 

 ducts were shown, and the experiments mentioned to several members of the 

 K. s. the beginning of last winter, particularly to the President, who honoured 

 the author with his attendance during several of the processes. 



The substance produced by M. Raymond, referred to in the Annales de Chimie, 

 is a humid combination of phosphorus and lime, and does not decompound cold 

 water; it is therefore a very different composition from the phosphur of lime de- 

 scribed in the above paper. 



XVI. Observations on the Atmospheres of Venus and the Moon, their res- 

 pective Densities, Perpendicular Heights, and the Tivilight occasioned by 

 them. By Johji Jerome Schroeter, Esq., of Lilienthal, in the Duchy of 

 Bremen. Translated from the German, p. 309. 



On the atmosphere of Venus. — Although the evidence afforded us by the most 

 recent observations and discoveries, not only of the existence, but also of the 

 various and singular properties of the atmospheres of Saturn, Jupiter, Mars, 

 and the Moon, be in a manner incontrovertible; yet so inconclusive are the few 

 observations hitherto made on the atmosphere of Venus, that several of the 

 greatest astronomers have lately thought themselves authorized to doubt its very 

 existence. 



What convinced me 12 years ago, when I first began to observe Venus with 

 a good 3-feet achromatic telescope that it actually has an atmosphere of no small 

 extent, was the striking diminution of light which I noticed on the planet in its 

 various phases from its exterior limb towards the interior edge of its illuminated 

 surface, and especially near the latter: and this appearance it was which induced 

 me to make further observations on the subject, especially as I found that the 

 phenomenon recurred as often as I looked at the planet with an Herschellean 4 

 and 7-feet reflector, armed with the higher magnifying powers. 



The great number of observations I have now made on this object, for a series 

 of years, being on the whole very similar in their nature and results, it would no 

 doubt be not only tedious, but also supjerfluous, to describe them here at length: 

 but the following general remarks it may be necessary to premise, in order to ob- 

 viate all misapprehension, and the false conclusions that might be deduced from 

 hasty and inaccurate observations. 



The light appears strongest at the outward limb, whence it decreases gradually, 

 and in a regular progression towards the interior edge or terminator, and this not 

 only towards its middle, but also near the two cusps, the light becoming so dim 

 immediately at this border, that it commonly loses itself in a faint bluish grey, 

 forming a very indefinite ragged margin, scarce discernible with the best teles- 



