282 HERSCHEL. 



manner we must endeavour to distinguish separately the 

 two members of certain double stars very close to each 

 other. He said if you wish to assure yourself that n 

 Coronas is a double star, first direct your telescope to a 

 Geminorum, to f Aquarii, to /" Draconis, to p Herculis, 

 to a Piscium, to e Lyras. Look at those stars for a long 

 time, so as to acquire the habit of observing such objects. 

 Then pass on to Ursae majoris, where the closeness of 

 the two members is still greater. In a third essay se- 

 lect i Bootis (marked 44 by Flamsteed and i in Harris's 

 maps) *, the star that precedes a Orionis, n of the same 

 constellation, and you will then be prepared for the more 

 difficult observation of y Coronas. Indeed n Coronas is a 

 sort of miniature of i Bootis, which may itself be consid- 

 ered as a miniature of a Gem. (Philosophical Trans- 

 actions, 1782, p. 100.) 



As soon as Piazzi, Olbers, and Harding had discov- 

 ered three of the numerous telescopic planets now known, 

 Herschel proposed to himself to determine their real 

 magnitudes ; but telescopes not having then been applied 

 to the measurement of excessively small angles, it became 

 requisite, in order to avoid any illusion, to try some ex- 

 periments adapted to giving a scale of the powers of those 

 instruments. Such was the labour of that indefatigable 

 astronomer, of which I am going to give a compressed 

 abridgment. 



* In the selection of i Bootis as a test, Arago has taken the precau- 

 tion of giving its corresponding denomination in other catalogues, and 

 Bailey appends the following note, No. 2062, to 44 Bootis. " In the 

 British Catalogue this star is not denoted by any letter: but Bayer 

 calls it, and on referring to the earliest MS. Catalogue in MSS. vol. 

 xxv., I find it is there so designated; I have therefore restored the 

 letter." (See Bailey's Edition of Flamsteed's British Catalogue of 

 Stars, 1835.) The distance between the two members of this double 

 star is 3" -7 and position 23 -6. See " Bedford Cycle." Translator. 



