VOL. LXXV.] PHILOSOPHICAL TRANSACTIONS. 653 



diameter not greater than Q", which sufficiently shows that this diameter sup- 

 posed 7" in the mean distance is also too great. 



IX. Observations of a Neiv Variable Star. By John Goodriche, Esq. p. 153. 



On Sept. 10, 1784, while my attention was directed towards that part of the 

 heavens where (3 Lyrae was situated, I was surprized to find this star much less 

 bright than usual, on which I suspected that it might be a variable star : my 

 suspicions were afterwards confirmed by a series of observations, which have 

 been regularly continued since that time, and which will presently follow in their 

 proper place. At first I thought the light of this star subject to a periodical 

 variation of nearly 6 days and 9 hours, though the degree of its diminution did 

 not then appear to be constant ; but now, on a more close examination of the 

 observations themselves, I am inclined to think, that the extent of its variation 

 is 12 days and 1Q hours, during which time it undergoes the following changes. 



1. It is of the 3d magnitude for about 2 days. — 2. It diminishes in about one 

 day and a quarter. — 3. It is between the 5th and 4th magnitude for less than a 

 day. — 4. It increases in about 2 days. — 5. It is of the 3d magnitude for about 3 

 days. — 6. It diminishes in about 1 day. — 7. It is something larger than a star 

 of the 4th magnitude for little less than a day. — 8. It increases in about 14 day 

 to the 1st point, and so completes a whole period. 



These 8 points of the variation are perhaps inaccurately ascertained ; and in- 

 deed it cannot be expected to be otherwise in estimations of this nature, where 

 it is very possible to err even several hours. The magnitudes of the stars to 

 which |3 Lyrae was compared during the progress of its variation, are as follow : 

 (3 Cygni and y Lyrae of the 3d magnitude ; g and 9 Herculis of between the 4th 

 and 3d magnitude ; Herculis is something less than a star of the 4th magni- 

 tude ; £, x, and S Lyrae are stars of between the 4th and 5th magnitude, if not 

 nearer the 5th. The relative brightness of these stars follows the order in which 

 they are set down. Then follows a series of daily observations and comparisons, 

 from Sept. 10, 1784, till Jan. 6, 1785. From which Mr. G. deduced his con- 

 clusions relative to the 8 points of the variation, as above stated. 



With regard to the period of the variation, Mr. G. proceeds, it is evident 

 from a collation of the preceding observations in a coarse way, that it is nearly 

 12 days and £ . To determine it with greater accuracy is a subject of consider- 

 able difficulty, in the present case ; for unless we can obtain very exact points of 

 comparison, the period would come out erroneous, especially if deduced from 

 intervals consisting of only a very few periods, as is the case here. However, as 

 I have been able to obtain a few observations of the middle of its obscuration in 

 the 3d point accurate enough for our purpose, I have formed the following 

 calculation. 



