WITH THE MICROSCOPE. 245 



angled head-piece is brought almost to touch the shutter, and the light 

 around the upright piece excluded by a thick curtain. The micro- 

 scope, which is a heavy one, is placed horizontally, and depending 

 from the screw. Fastening the arm of the instrument to the rack, is 

 a stiff piece of flat brass, pierced at its lower part to support the end 

 of a rod suspended beneath the base-board, and provided at the end 

 with a grooved pulley of the same diameter as the milled head of 

 the fine adjustment, which is also grooved, a small endless band 

 connecting them. The depending piece passes through a slot cut 

 in the base-board, equidistant from the sides, and permits the rack of 

 the coarse motion being worked, or the movement of the microscope 

 backwards or forwards, the rod following it. This was the plan 

 recommended in the last edition. The rod is placed beneath the 

 board to be out of the way, and not to interfere with the traversing of 

 the frame which carries the screen or sensitive plate. This frame is 

 made with a heavy base the width of the board, and has side clamping 

 screws. By means of a central pin, between the two parts which form 

 the heavy base, it is capable of slight rotation on its vertical centre, 

 to compensate for any want of parallelism in the parts right and 

 left of the object, or for stereoscopic negatives. The square frame 

 is hinged to the top of this base, to allow of slight motion forwards 

 or backwards, being supported at the sides by two brass struts which 

 have a clamping pin on each side. To arrange for glasses of various 

 sizes, two bars undercut slide up and down the uprights of the frame 

 and can be fixed at any distance apart by clamping nuts. The 

 motion of the frame will often help to secure a perfect parallelism 

 with the object on the slide. The screen may be either plane finely 

 ruled plate glass, a collodion prepared washed plate over which a 

 little albumen or tannin has been flowed, or the plate employed 

 occasionally by Dr. Maddox ;* or the plate may be prepared as has 

 been recommended for ordinary camera purposes by Mr. M. Carey 

 Lea, of Philadelphia (whose contributions to the British Journal of 

 Photography are marked with much originality and utility). Thin 

 well-boiled starch is filtered through muslin, then poured to the 

 depth of the tenth of an inch on to a clean polished plate of glass, 

 set level, and allowed to dry spontaneously, but quickly. It must 

 not be put in a drawer, for fear of it drying too slowly and the 

 surface being irregular. Or, as in Mr. Wenham's method, p. 236, the 

 image can be examined on a card, held as the glass screen or 

 sensitised plate, by two springs from the transverse sliding bars. 



* Some closely filtered stale milk, either with or without a little weak solution 

 of gelatine, poured on a plate of glass set parallel, and dried quickly. 



