jr eat magnifying Powers ufed by Mr, Hedchel. 177 
light iti the object, and a very confiderable aberration which 
takes place, and makes the picture too indidinft to be very ac- 
curate in the meafure, and of courfe larger than it ought to be; 
and this will account for the excefs in the meafures of my two 
larged: powers. However, when I employed 6450 upon the 
diameter of a Lyras, 1 incline to think the method I had ufed 
when I determined that power, ought to be preferred, becaufe 
mv Lamp-micrometer gives the meafure of an object as it ap- 
pears in the telefcope, and therefore this aberration is included, 
ard fhould be taken into confideration. 
' *- f 
To prevent any miftakes, I wifh to mention again, that I 
have all along proceeded experimentally in the ufe of my powers, 
and that Ido not mean to fay I have ufed 6450 (or 5786) upon 
the planets, or even upon double dars ; every power I have 
mentioned is to be underftood as having been ufed jud as it is 
related ; but farther inferences ought not as yet to be drawn. 
For indance, my obfervations on e Bootis mention that I have 
viewed that dar with 2010 (or as in the above table with 2175) 
extremely didinfl ; but upon feveral other celedial objects I 
have found this power of no fervice. Many plaufible fug- 
gedions have already occurred to account for thefe appearances; 
but I wait till farther experiments fhall have furnifhed me with 
more materials to reafon upon. The ufe of high powers is a 
new and untrodden path, and in this attempt variety of new 
phenomena may be expected, therefore I wifh not to be in 
a hade to make general conclufions. I fhall not fail to purfue 
this fubje£t, and hope foon to be able to attack the celedial 
bodies with a dill dronger armament, which is now pre- 
paring. 
A a 
Vol. LXXII. 
It 
