Mr. Atwood’s Theory for the Menfur niton 
the angle of incidence on the fixed fpeculum j the correfponding reparation of 
the images will tag?*”* * ^(P- 4=9-) which is the greateft poftlble 
V i - ?n l -f rn z f 
when p 
q — - iom+m L '--- 3- yn _ 
~~ Iff? 
fine of 35 
0 11' 47" ( ;r 
if m 
fm. 7% 
as ;n 
and s = fin. t o', asin tab. I. and IT.) being then = — , but if r^fin. 30", 
tab. III. the greateft reparation will be only JL-, correfponding to lefs than one- 
third of a decree for the images motion through to' in the field of the telefcope. 
In like manner let a line be drawn through the center of the field perpendicular to the 
line before defcribed, any deviation of the points in contact through a finall angle 
/in the direaion of this line will caufe the plane of refleaion at the fixed fpeculum 
to be inclined to the primitive fecondary with which it Ihould coincid e at a n an gle _ 
• 4.mp z s‘e xV'i-fxv'i-f* 
1. this will occafion a reparation of the images _ —======- 
rn 
rn -\-m~p 
{page 429. L being there fubftituted for d) which is the greateft polfible when 
^ If m - fin. 7 0 and s - fin. 10', as in tab. I. and II. 
4 m 
d 
the greateft reparation of the images will be — ig ^ I+g9 (, * but ,f 1 C “’ J 
, ttt • mi — e - ^ — , which anfwers to 
and m=fin* 7°, as in tab. IH. it will only - 2mio 
a divarication of lefs than l'" for the images motion through 10' in the field 
”f the telefcope, in the direflion of the line above defcribed, which is drawn 
though the center of the field, and perpendicular to the fixed plane of reflexion. 
It muft be remembered, that the legations of the images here elated are 
greater than can poffibly happen in thefe conftniftions, when t e in 
direaed to any other points of the circumference of the plane of motion i(*e 
difiance of the images from the center the field not exceeding ro ) are, 
even in this cafe, phyfically fpeaking, evanefcent. 
table 
