1836.] 



Results at the Madras Observatory. 



53 



In addition to which I might now swell this list, by giving the par- 

 ticulars with regard to observations made of Halley's Comet — the oc- 

 cupation of stars and planets by the moon— the transit of Mercury 



over the sun'a disc observations made during the hot land-wind, 



compared with those made at other times, &c. &c. — all of which, al- 

 though eminently tending to advance the cause of Astronomy, would, 

 nevertheless, increase this article to a length which would be consider- 

 ed tedious, and beyond that which 1 had intended at its commencement. 



I will therefore further notice two points, only, which have been 

 canvassed in the Madras Results. The first is the annual parallax of a 

 Aquitog. 



If an observer, situated at any fixed star, were to measure the sub- 

 tense of the diameter of the earth's orbit, by an easy trigonometrical 

 computation, we should at once arrive at a knowledge of the distance of 

 the said star ; but if, as generally has been supposed, the earth's orbit,, 

 190,000,000 miles, subtends no appreciable angle, in this case the dis- 

 tance of the star falls short only of infinity. 



The star in question ( a Aquilce) has, with several others, engaged 

 the attention of those Astronomers who possess the means of making 

 observations of this nature, from the earliest times ; and, in proportion 

 as the means for obtaining an accurate result have increased, just in 

 that same ratio has the assigned quantity of parallax diminished. 



On one occasion, the Astronomer Royal of Dublin obtained the gold 

 medal of the Royal Society, for having detected in «- Aquilce an annual 

 parallax of two or three seconds; and, in the succeeding year, 

 the Astronomer Royal at Greenwich obtained the same medal for 

 proving that such was not the case. 



It would be disingenuous here to offer an opinion upon the modus ope- 

 randi pursued by these individuals, (on which the result mainly depends). 

 I will therefore proceed to state, that the Dublin results have been com- 

 pletely confirmed by the Madras Observations ; the annual parallax 

 amounting to i'96, giving the distance of this star from the earth 

 19,104,200,000,000 of miles. 



Lastly (since it is the last result obtained from the Madras Observa- 

 tions), we will examine the determination of the proper motions (as they 

 are called) of the fixed stars. 



By reason of refraction, and the earth's motion in its orbit, combined 

 with the velocity of light, the distance of one fixed star from another, 

 as measured by astronomical instruments, is continually liable to change ; 

 and, in the case if stars situated so near the Earth as a Aquiloe, a 

 further cause of change is found. When these knoicn variations are 

 computed and allowed for, if the place of the star from year to year 

 does not conform to the known variations of its place, it follows, either 

 that the star must have some motion of its own, or that its place has 

 changed from a movement of our system. In either case the amount 



