244 HOW T0 WORK 



at the time of making any alteration in the fine motion. A lever 

 arrangement has been used to obviate this, but if employed with the 

 high powers it is extremely difficult to prevent a slight slip of the screw. 

 Mr. Legg employed a lever crank and arm over the top of the camera, 

 working on the milled head of the coarse rack and pinion motion. 

 Professor Rood, of Troy, N.Y., also made use of a rod and lever 

 beneath the camera, acting on the rack work, and a hinged mirror 

 placed this side of the ground glass to receive the image transmitted 

 to it while arranging the object on the stage plate, and attending to 

 the illumination. 



Dr. Maddox, who has much improved the before-mentioned 

 apparatus, after trying several methods for supporting the rod, gave 

 the preference to that described under his method of working with- 

 out a camera in a darkened room. The rod being placed beneath 

 the base-board, in which position it is less liable to accidental disar- 

 rangement, but in this case a stronger microscope will be required. 

 Messrs. Powell and Lealand have lately made for me, according to 

 some suggestions of Dr. Maddox, a stand which is steadier and pos- 

 sesses some advantages over that just described. 



The chief requirements in any form of camera, independent of 

 the objective or mode of illumination, are general facility of manage- 

 ment, compactness within a moderate range of extension, correct 

 centering, freedom from vibration, and the total exclusion of all light 

 except that which enters by the object-glass. 



33O. Dr. Itladdox's Arrangement for Working without a Camera. 

 In order to take photographs without a camera, a room has been 

 fitted up by Dr. Maddox as a dark chamber, the top sash of the 

 window being darkened, and the place of the lower sash when 

 thrown up supplied by a shutter with a large central opening ; an 

 oblong aperture exists at the right side of the shutter, protected 

 by a frame glazed with yellow glass, which slides up and down, 

 and is kept in position by a spring. The aspect happens to be 

 direct S.W., and, unfortunately, very much exposed to the strong 

 south-westerly winds ; therefore to try and avoid the tremor occa- 

 sioned by such a large surface as the shutter affords, no pait 

 of the microscope is fixed to it, but rests on a long stout base- 

 board, supported on four double triangle legs. The shutter end is 

 clamped by two screws, an upright piece at right angles, pierced to 

 permit the attachment of a 3|-inch solar condenser with its small 

 condensing lens, the mirror of which is passed through the aperture 

 in the shutter. This is worked by a double milled head from the 

 inside, the ammonio-sulphate of copper cell being placed between 

 the mirror and the condensing lens. The base-board with right 



