Parsons.—On a Reflecting Telescope made in Wellington. 125 
S; and because a uniformly accelerating 
force is measured by twice the space 
described from rest in one second, and 
it is found by experiment that the force 
of gravity on the earth’s surface causes 
a body to fall from rest a distance of 
16:1 feet in the first second of time, 
consequently the force of terrestial 
gravity g= 32-2 feet, that is, this 
force continuously soliciting a falling 
Fig. 5. body, will accelerate its velocity 32-2 
feet every second; therefore 2AE expresses the intensity of gravity acting 
on A. Join BA ; then since the are AB differs insensibly from its chord 
(for the time of devcthinn it may be made as small as we please) we may 
regard ABA’ as a right — plane triangle since the angle B is in a 
semicircle, therefore AE: AB : A’ 
AB? AB? AB? v? 
S AE=7p = ag 2AE=Tg => 
Now 2AE represents the accelerating force at S, or taken in an opposite 
direction, it represents the centrifvgal force 4 and AB i aca the velocity 
vin the curve ; consequently the centrifugal force f= as where 7 =radius. 
If, as is usual, n be made to stand for the number 3'14159, etc., the whole 
circumference of the circle will be 2nr ; therefore calling the whole time of 
describing the circumference—that is the periodic time, t—then the uniform 
velocity v being equal to the whole space divided by the whole time we have— 
Dnr 4n2r 
ft ge monies t $ remmend 2 ? 
i Qnr ww nr Aner 4 72 
for if v= ; the = =; 
Deviation from the parabolic figure arising from the earth’s sphericity only 
amounts, to of an inch at the circumference of a speculum four feet in 
diameter. 
871200 
Art. XIL.— Description of a Reflecting Telescope made in Wellington by 
W. F. Parsons. Communicated by James HECTOR, MD, FRS 
[Read before the Wellington Philosophical Society, 23rd October, 1872.] 
THE instrument which I exhibit is a Newtonian model, with a silvered-glass 
speculum, and with the exception of the eye-pieces has been wholly made in 
Wellington by following the directions given in a paper by Mr. W. Purkiss, 
