22 



thread directly between the stars, and when the Comet ap- 

 proaches the horizon try again whether it continues in the 

 same right lino, between the same two stars. If there be any 

 sensible parallax which depresses the Comet, it will not be 

 seen in the same right line in both situations, but if the line 

 is threaded by the two stars and Comet, it is a convincing 

 proof that they have in these positions no sensible parallax, 

 and must be at an enormous distance ; refi'action in this case 

 will equally effect both Comet and Stars, and therefore need 

 not be regarded. 



The approximate distance of a Comet from the Earth — and 

 its distance from the Sun, may be found by Plane 

 Trigonometry. The length of a line drawn on a celestial 

 globe or chart, from the position of the Sun to that of the 

 earth, is known fi'om the last transit of Venus to be 95,273,868 

 miles, a second line then drawn from the position of the Sun 

 in the direction of the Comet's tail, and meeting a third line 

 drawn from the earth to the Comet, will form a triangle, from 

 which the two latter sides, or distance of the Comet from 

 the Sun and earth may be computed, and if carefully conducted, 

 especially if cleared from parallax and refraction, they will be 

 found sufficiently near to correct the many contradictory and 

 embarrassing statements, that during the apparition of the late 

 Comet have found their way into the public prints. They are 

 also sufficient for identification, and will enable anyone to 

 ascertain whether the computed elements differ from authorised 

 catalogues, upon the inclination of the plane of the orbit ; 

 upon the longitude of the node ; and upon the longitude of 

 perihelion distance. When these parabolic elements are found 

 none resemble any of those recorded in catalogues of cal- 

 culated Comets, we are justified in concluding that it had not 

 been observed before. 



From the foregoing rule the recent Comet's approximate 

 distance was found by a vertical angle to be on tho 21st 

 January — From the earth, 88,000,000 of miles ; from the Sun, 

 42,000,000 of miles. January 28th — From the earth, 

 92,000,000; from the Sun, 62,000,000. February 4th— 

 From the earth 98,000,000; from the Sun, 73,000,000. 

 February 18th— From the earth, 110,000,000 ; from the Sun, 

 98,000,000. Assuming the Sun's distance from the earth to 

 be 93,500,000 of miles, which, from more recent observations, 

 is probably nearer the truth, from these distances it will be 

 apparent that the Comet was receding from the earth at its 

 first appearance, on the 17th January, and must have passed 

 the perihelion before it was seen at Hobart Town. 



The low position of the Comet, together with the unusual 

 cloudiness of the evenings, rendered it difficult to get suitable 

 stars to observe with it. In obtaining the following positions 



