1 6 6 Mr. herschel’s Defcription of 
to a hook at o (not expreflfed in the figure being at the back of 
the arm L), and palling along the groove from oh to q is turned 
over a pulley at q , and goes down to a fmall barrel e , within 
the plane of the circular board, where a double-jointed handle 
eP commands its motion. By this contrivance we fee the arm 
L may be lifted up to any altitude from the horizontal pofition 
to the perpendicular, or be fuftered to defcend by its own 
weight below the horizontal to the reverie perpendicular fitua- 
tion. The weight of the handle P is fufficient to keep the 
arm in any given pofition ; but if the motion fhould be too 
eafy, a friflion fpring applied to the barrel will moderate it at 
plea fu re. \ 
In front of the arm L a fmall Aider, about three inches 
long, is moveable in a rabbet from the end L towards the cen- 
ter backwards and forwards. A firing is faflened to the left 
fide of the little Aider, and goes towards L, where it pafles 
round a pulley at m, and returns under the arm from m, v, 
towards the center, where it is led in a groove on the edge of 
the arm, which is of a circular form, upwards to a barrel 
(railed above the plane of the circular board) at r, to which 
the handle rD is faflened. A fecond firing is faflened to the 
Aider, at the right fide, and goes towards the center, where it 
pafles over a pulley n, and the weight w, which is fufpended 
by the end of this firing, returns the Aider towards the center 
when a contrary turn of the handle permits it to afl. 
a and b are two fmall lamps, two inches high, i\ in breadth 
by 1 1 in depth. The fides, back, and top, are made fo as to 
permit no light to beleen, and the front confifls of a thin brafs 
Aiding door. The flame in the lamp a is placed three-tenths of 
an inch from the left fide, three-tenths from the front, and 
half an inch from the bottom. In the lamp b it is placed at 
the 
