I c4 Mr. Goodricke's Obfervations 



inclined to think, that the extent of its variation is Hvelve days 

 and nineteen hours^ during which time it undergoes the fol- 

 lowing changes. 



1. It is of the third magnitude for ahout two days. 



2. It diminifhes in about one day and a quarter. 



3. It is between the fifth and fourth magnitude for lefs thau 

 a day. 



4. It increafes in about two days. 



5. Itr is of the third magnitude for about three, days. 



6. It dinnniflies in about one day. 



7. It 's fomething larger than a ftar of the fourth magnitude 

 for little lefs than a day. 



8. It increafes in about one day and three quarters to the firft 

 point, and fo completes a whole period. 



Thefe eight points of the variation are perhaps Inaccurately 

 afcertained ; and indeed it cannot be expeded to be otherwife in 

 efiiimations of this nature, where it is very poffible to err even 

 feveral hours. 



The relative brightnefs of /G Lyras, at its obfcuration in the 

 third and feventh points, is nearly as follows. When in that of 

 the third point, it is lefs than f and x, and nearly equal to 

 ^ Lyras ; and when in that of the feventh point, it is rather 

 lefs than £ and ^ Herculis, and much brighter than f, y,^ and 

 I Lyras. At its greatefl brightnefs in the firft and fifth points, 

 it is fometimes brighter than y Lyras, but lefs than /G Cygni, 

 and fometimes only nearly equal to it ; but in thofe points it 

 feems to alter in its brightnefs feveral times in the fame night, 

 and that generally In a pretty confiderable degree. However, 

 this may perhaps be only owing to fome fallacy of obfervation ; 

 for I have often perceived, that the relative brightnefs of ftars 

 is affedled not only by the different flates of the air, but alfo by 



their 



