37 ° Dr. Herschei/s Account of the Changes 
minuteness of the two that have been observed with tt, as well 
as the distance of the farthest, render a connection between the 
three stars very improbable; nor can the change of situation be 
owing to parallax, as this would have occasioned a retrograde 
motion of the small star, which, on the contrary, has been direct. 
From these considerations we may conclude, that tt Arietis has 
a proper motion, to which we must look for the cause of the 
observed change. 
vi Corona. I, 1 6. 
This very minute double star has undergone a great alteration 
in the relative situation of the two stars. Sept. 9* 1781, their 
position was 59 0 19' north-following ; and. Sept. 6 , 1802, by a 
mean of two very accurate measures, it was 89° 40' north-pre- 
ceding; which amounts to a change of 31 0 1', in 20 years and 
362 days. The distance of the two stars has not been subject to 
any sensible alteration. Sept. 9, 1781, a very small division 
might be seen, with 460. August 30, 1794, they were so close 
that, with a' 10-feet reflector, and power of 600, a very minute 
division could but just be perceived. April 13, 1803, with a 
10-feet reflector, a very small division was also visible, with 400, 
though better with 600. And, May 15, 1803, I saw the sepa- 
ration between the two stars, with the same 7-feet reflector, and 
magnifying power of 460, with which I had seen it 22 years 
before. The stars differ very little in magnitude ; so that we 
•have no reason to expect any effect from a difference of parallax. 
Besides, if the small one were out of the reach of it, a parallactic 
motion of the largest alone, would have occasioned the small one 
to move apparently according to the order of the signs ; but the 
motion has been retrograde. 
