A REFRACTING TELESCOPE WITH A FLUID CONCAVE LENS. 43 
when thrown out beyond its perpendicular position, as is necessary to bring the 
instrument to small angles of elevation. 
This counterpoise is not, however, sufficient ; another therefore is introduced, 
by suspending a chain from the swinging frame to the front stancheon ; to the 
centre of which a 56-pound weight is suspended, passing over another pulley 
on the brace into the same well-hole : by this contrivance the tension of the 
chain increases as it approaches most to a straight line ; that is, when the 
frame is thrown furthest out, and where its weight acts with greater force. 
By a slight adjustment of the length of the chain and weight, we may thus 
produce a perfect equilibrium in the whole machine, and the telescope is of 
course obedient to the slightest power sufficient to overcome the friction. 
Things being thus equipoised, in order to render the motion as gentle as 
possible, a wheel and pinion are attached to the barrel last mentioned, similar 
to the one already described, but with four cross handles like those belonging 
to the screw. The power thus gained is 2 to 1 by the pulleys, 4 to 1 by the 
wheel and pinion, and about 9 to 1 by the handles, equivalent to 72 to 1 . The 
slightest touch therefore of one of these handles will produce a change of ele- 
vation of the telescope, either to increase or diminish it, accordingly as that 
motion tends to pull in or out the swinging frame. 
The operation therefore of putting the instrument on a star is : first, to swing 
round the whole stand towards the star, on the circular curb ; then to bring it 
nearly to its proper altitude by the apparatus first described; then, being 
seated at a proper height, the eye being applied to the finder, with the handle 
belonging to the screw in one hand and that belonging to the altitude motion 
in the other, the star is brought immediately to the centre of the field, and is 
of course then in the large telescope. The observer is thus seated at perfect 
ease and follows the star at pleasure, one of the four handles on each side 
being always ready to receive a touch of the finger, which is sufficient for the 
purpose. 
I have observed that this stand acts with considerable accuracy as an alti- 
tude and azimuth instrument : it may therefore be proper to say a few words 
on this subject. Such a purpose was not contemplated in its construction, and 
therefore, notwithstanding the usual accuracy of millwright workmanship, it 
could hardly have been expected to find the stand susceptible of such a degree 
g 2 
