[ 418 ;] 
XVII. Some account of the transit instrument made by Mr. 
Dollond, and lately put up at the Cambridge Observatory, 
Communicated April 13, 1825. By Robert Wood house, 
A. M. F. R. S. 
Read May 19, 1825. 
As I am inclined to hope that the observations to be made 
at the Observatory lately established at Cambridge may, at 
some future period, be useful to astronomical science, I beg 
leave to send a brief description of our transit telescope, the 
only large instrument which we are at present possessed of. 
The annexed drawings, which I have caused to be made of 
the instrument, will explain its construction. 
Its dimensions are nearly the same as those of the Green- 
wich transit made by Mr. Troughton. 
Ft. In. 
Its focal length is - - - 9 10 
Its aperture - - -05 
The length of the axis between the piers 3 6 
The weight of the instrument is 2oolbs. 
The instrument is counterpoised ; and the whole lengths 
( 2 inches ) of the pivots rest on the Y s. 
Seven fixed wires are placed in the fociis of the object 
glass, and two other wires moveable by a micrometer screw ; 
the interval of which wires is equal to the interval between 
any two of the fixed wires, and, equatorially , is i7*.88. 
The two small graduated circles (see the figure) with 
their spirit levels, fixed near to the eye- piece, are for the 
