154 A/A Goodricke's Obfervations 
inclined to think, that the extent of its variation is twelve days 
and nineteen hours , during which time it undergoes the fol- 
lowing changes. 
j . It is of the third magnitude for about two days. 
2. It diminifhes in about one day and a quarter. 
3. It is between the fifth and fourth magnitude for lefs than 
a day. 
4. It increafes in about two days. 
5. It is of the third magnitude for about three days. 
6. It diminifhes in about one day. 
7. It is fomething larger than a flar of the fourth magnitude 
for little lefs than a day. 
8. It increafes in about one day and three quarters to the firfl 
point, and fo completes a whole period. 
Thefe eight points of the variation are perhaps inaccurately 
afcertained ; and indeed it cannot be expected to be otherwile in 
eflimations of this nature, where it is very poffible to err even 
feveral hours. 
The relative brightnefs of j 3 Lyras, at its obfeuration in the 
third and feventh points, is nearly as follows. When in that of 
the third point, it is lefs than f and and nearly equal to 
^Lyrae; and when in that of the feventh point, it is rather 
lefs than | and 0 Herculis, and much brighter than x, and 
J.Lyrae. At its greatefl brightnefs in the firfl and fifth points, 
it is fometimes brighter than y Lyrae, but lefs than /3 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 flars 
is, affedted not only by the different flates of the air, but alfo by 
their 
