2140 Journal of Applied Microscopy 



of cold water can be carried through the cell when projecting living forms, if 

 desired. In order, however, to obviate the necessity of this procedure, for ordi- 

 nary work, two water cells are furnished, and when one becomes warm it is only 

 necessary to lift it out and set another in its place. Fig. 3 shows the construc- 

 tion of the condenser system and water cell in detail. Fig. 4 shows the parts 

 assembled for the projection of lantern slides. The steel bar carrying the 

 optical parts is mounted upon a base-board which is hinged to a wooden sup- 

 port at the rear end, and provided with elevating screws in front, so that the 

 circle of light may be centered upon the screen with the greatest facility. The 

 projection lens is carried upon the first support, to the front of the iron frame 

 of which it is attached by the catch and pins before described. The bellows 

 connects the lens with the support carrying the object carrier to prevent the 

 escape of light into the room, and to the rear of the object carrier is found the 

 condenser system with water cell. This water cell is a very great advantage 

 even in ordinary projection work, owing to its absorbing a large part of the heat, 

 and thus preventing the cracking of valuable slides, which occurs continually 

 unless some such precaution is used. At the rear of the condenser system 

 we find the lamp hood, of Russia iron, with door at the side and rear, open 

 space at the bottom and hood at the top, by which ventilation is secured to pre- 

 vent heating. 



The illuminant may be either acetylene, oxy-hydrogen, lime light, or electric 

 arc. The two former lights have not yet received much consideration, but a very 

 convenient hand feed electric arc lamp has been devised. This lamp consists of 

 a vertical support on which two arms at right angles are carried, the vertical arm 

 carrying the vertical carbon, and horizontal arm carrying the horizontal carbon 

 in the optical axis. Each carbon carrier is moved by a quick acting screw, the 

 horizontal screw being actuated by a non-conducting milled head projecting 

 through an opening in the rear door of the lamp-hood, thus being operated from 

 the outside when the door is closed. The vertical carbon is actuated by a simi- 

 lar milled head slightly smaller in size immediately back of the milled head actu- 

 ating the horizontal carbon, and connecting with the vertical carbon by means 

 of a horizontal shaft which traverses the length of the shaft operating the hori- 

 zontal carbon and connecting with the vertical quick acting screw by means of a 

 mitre gear, thus both carbons can be moved simultaneously by placing the 

 fingers upon the two milled heads, or each carbon can be moved independently 

 by actuating its respective milled head, at the rear, the condition of the arc being 

 observed through a dark-glass window in the side door. Vertical motion of the 

 whole lamp is accomplished by means of a non-conducting milled head placed 

 beneath the vertical carbon, and easily accessible, lateral motion being effected 

 by another milled head in close proximity to that by which the vertical motion is 

 secured. The whole lamp is carried on a slide piece by which it can be moved 

 backward and forward in the optical axis. A thumb-nut is provided for holding 

 it rigidly in position when the desired focal point has been secured, thus with 

 projection lenses of different foci, or for altering the focal point of the condens- 

 ing lenses in various physical experiments, it is desirable to alter the distance of 

 the arc from the rear condensing lens. This is very easily accomplished with- 



