1 836.] 



Results at the Madras Observatory. 



51 



density of this ether has been computed, from the observations hitherto 

 made, to be eight hundred times lighter than atmospheric air. 



8th. Observations to determine the annual parallax of the principal 

 fixed stars. 



9th. Observations of the proper motion of double stars around one 

 another, and of the fixed stars generally. It has been supposed and it 

 appears very probable, that the solar system is in motion in space ; to 

 determine which, accurate, as well as long continued, observations of 

 the proper motions of the fixed stars are necessary. 



There are, in addition to the above, several other desiderata, which, 

 being of minor importance, and forming a very numerous class, it might 

 be tedious here to notice. 



With regard to the points, to which the observations made at the 

 Madras Observatory have been directed, I may call them those of a 

 general nature ; hence it will be as well to mention them in the order in 

 which they occur in the Madras Results. 



In the first place, the determination of the mean diameter of the sun, 

 is one to which some considerable attention has been paid, with a view 

 to discover if any difference existed between the solar and equatorial 

 diameters. Our observations of all the planets (including the Earth), 

 shew that the difference of their equatorial andpolar diameters varies, in 

 proportion to the rapidity of the motion on their respective axes : a fact 

 which immediately results from supposing the particles composing the 

 planets to be capable of yielding. In the case of the sun, then, which 

 revolves on its axis in 26 days, a very small amount of difference should 

 result. M. La Place computes its amount to be less then one second of 

 space. 



The observations made here for this purpose are as follows : 1 " 



From 965 observations of the Equatorial semi-diameter 16 1,48 



141 .Polar semi-diameter , 16 1,59 



The small difference which is here observed, in a contrary direction 

 to what might be expected, is no doubt due to error of observation. This 

 accounted for, we may assure ourselves that the sun is perfectly spheri- 

 cal, and that it is composed of solid and unyielding materials. 



"With regard to the Sun's distance from the Earth, the observations 

 made of the planet Mars, and of stars situated near to his path at the 

 times of opposition in 1832 and in 1834, when compared with similar 

 observations made at the Cape of Good Hope Observatory, enable us to 

 compute the angle, under which an observer situated at the planet 

 Mars, would view these two observatories. 



Now the relative distances of the planet Mars and the Earth from 

 the Sun, are known from the laws of gravity ; hence, from the above 

 measure of the angle under which the Madras and Cape Observatories 

 appear at the planet Mars, we can compute what would be its measure 

 at the Sun, and, the geographical situation of the observatories being 



