148 Mr. G. M. Minchiu. [May 16, 



A thin plate of brass AA with a circular hole of about '75 cm. 

 diameter in the centre of its vertical face (not represented in the 

 figure) is fitted with a screw, S, at one end. This screw pushes 

 forward another thin brass plate, DD, which moves backwards and 

 forwards in a grooved space in the plate AA. The plate DD has 

 likewise a hole in its centre and is moved in one direction by S and 

 in the opposite direction by the finger applied to a screw F, attached 

 to DD near one end. A small thin brass plate, gg, is attached to 

 DD, and can move up and down (i.e., at right angles to the plane of 

 the figure) in a grooved space in DD by means of a screw which is 

 not represented in the figure. This plate gg has also a hole in its 

 centre over which is cemented a thin circular glass plate carrying 

 crossed spider lines, represented in the figure by + The point of 

 intersection of these cross-lines is capable of being brought into any 

 desired position by means of the horizontal motions of the plate DD 

 and the vertical motions of gg. 



To the face of AA opposite to that on which DD moves is attached 

 a thin brass plate, BB, which moves in a grooved space in AA. 

 Through BB passes a screw, s, which penetrates a short distance into 

 a special groove in BB which is terminated at the points marked 1 

 and 2. These points are, therefore, stops to determine the extreme 

 positions of the sliding plate BB on the fixed plate AA. 



The plate BB has a circular hole of about '75 cm. in diameter in its 

 middle, and also another, h, a little to the side. Over In, is cemented 

 a thin plate of glass on which can be marked two cross-lines marked 

 + in the figure, or a dot. 



An ebonite block with a cylindrical hole, C, into which fits the 

 cell represented in fig. 2 is screwed to BB just over the central hole 

 inBB. 



The plate BB is moved backwards and forwards by a projecting 

 handle, H. 



The fixed plate AA is screwed to a stout cylindrical tube about 

 two inches long (not represented), and this tube fits on the telescope 

 instead of the usual eye-piece. AA can be adjusted, if necessary, 

 to various positions relative to this tube, i.e., relative to the 

 telescope. 



To set the apparatus for a star, the procedure is this : move the 

 plate BB (and with it of course the cell) by the handle H until it is 

 stopped by the stop 2 ; move the intersection of the cross-lines on gg 

 by means of the screw S and the screw which moves gg vertically 

 until this point of intersection is exactly opposite the centre of the 

 sensitive surface of the cell (which is, of course, visible through all 

 the holes in the plates) ; bring back BB by means of H until it is 

 stopped by the stop 1 ; the glass plate covering the hole h is now 

 visible opposite gg or rather through h we can see the intersection 



