VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 213 



If neither of the stars should be in the ecliptic, nor have the same longitude 

 or latitude, the last theorem will still serve to calculate the total parallax whose 

 maximum will lie in e. There will also arise another parallax, whose maximum 

 will be in the conjunction and opposition, which will be divided, and lie on dif- 

 ferent sides of the large star; but as we know the whole parallax to be exceed- 

 ingly small, it will not be necessary to investigate every particular case of this 

 kind; for, by reason of the division of the parallax, which renders observations 

 taken at any other time, except where it is greatest, very unfavourable, the forms 

 would be of little use. 



To finish this theory, I shall only add a general observation on the time and 

 place where the maxima of parallax will happen. When 2 unequal stars are 

 both in the ecliptic, or, not being in the ecliptic, have equal latitudes, north or 

 south, and the larger star has most longitude, the maximum of the apparent 

 distance will be when the sun's longitude is gO c more than the stars, or when 

 observed in the morning; and the minimum when the longitude of the sun is 

 go less than that of the star, or when observed in the evening. When the small 

 star has most longitude, the maximum and minimum, as well as the time of 

 observation, will be the reverse of the former. When the stars differ in latitudes, 

 this makes no alteration in the place of the maximum or minimum, nor in the 

 time of observation; that is to say, it is immaterial whether the largest star has 

 the least or the most latitude of the two stars. 



XII. Catalogue of Double Stars. By Mr. Herschel, F.R.S. p. 112. 



Introductory Remarks. — The following catalogue contains not only double 

 stars, but also those that are treble, double-double, quadruple, double-treble, 

 and multiple. The particulars I have given of them are comprehended under the 

 following general heads. 1 . The names of the stars and number in Flamsteed's 

 catalogue; or, if not contained there, such a description of their situation as 

 will be found sufficient to point them out. 2. The comparative size of the stars. 

 On this occasion I have used the terms equal, a little unequal, pretty unequal, 

 considerably unequal, very unequal, extremely unequal, and excessively unequal, 

 as expressing the different gradations to which I have endeavoured to affix always 

 the same meaning. 3. The colours of the stars as they appeared to me when I 

 viewed them. Here I must remark, that different eyes may perhaps differ a 

 little in their estimations. I have, for instance, found, that the little star which 

 is near a. Herculis, by some to whom I have showed it has been called green, 

 and by others blue. Nor will this appear extraordinary when we recollect that 

 there are blues and greens which are very often, particularly by candle-light, mis- 

 taken for each other. The situation will also affect the colour a little, making 

 a white star appear pale red when the altitude is not sufficient to clear it of the 



