242 HOW TO WORK 



The whole of these arrangements are fixed firmly by the screw 

 and nut at the jointed ends of the stem, to a rectangular cross piece 

 of 3-i6ths iron bar about two inches wide, the screw passing through 

 a hole near its centre. This cross piece is turned down at right 

 angles on each side so as to bring the centre of the short microscope 

 tube in the centre of the camera, then again turned at right angles 

 and firmly screwed to a stout base-board of deal i^ inches thick, 

 1 2 inches wide, and 48 inches long, and clamped at each end to 

 prevent warping. This is supported over a wide moveable triangle, 

 having stout double-hinged triangle legs of a height convenient for 

 the operator (3 to 4 feet), pi. LIII, fig. 304 A. About 12 inches 

 from the end of the base-board where the microscope is fixed, is 

 hinged a stout square frame with a sliding door having a central 

 aperture to allow the end of the microscope tube to work through. 

 The inside of the aperture is lined with leather, and a thick velvet 

 collar is made to slide along the tube and abut against the aperture 

 in the door, so that when in use the entrance of any extraneous light 

 is effectually prevented. The frame with door is turned on its 

 hinges, until it stands exactly at right angles with the axis of the 

 microscope, and is kept firmly fixed in this position by two stout 

 brass strutts with clamping screws, that rise from the base-board on 

 each side of the frame at an angle of 60. At the opposite end of 

 the stout plank is placed an ordinary camera with a moveable door- 

 front having a large central aperture. One end of an expanding 

 bellows body is fastened to it, the other end being attached to the 

 door that slides into the vertical frame. This bellows part is made 

 of two thicknesses of black twilled calico, having pasted between 

 them a corresponding sized sheet of stout brown paper, and folded 

 into one-inch plaits when damp, then turned over square to the size 

 corresponding to the sliding doors, the corners bent down like the 

 bellows of a common accordion, and the overlapping edges which 

 are turned so as to face the base-board are double sewn together 

 throughout their length ; or for this may be substituted a body of 

 black calico, of treble thickness, attached at each end to the doors, 

 and kept apart laterally by elastic bands sewn along its four edges, 

 lengthwise. The camera is made to slide along the supporting board 

 between wooden guides screwed to its upper surface near the sides, 

 extending from the near end to the vertical frame. These have 

 small holes at corresponding equal distances of half an inch, and 

 projecting from each side of the body of the camera is a pierced 

 horizontal ledge of brass plate, about 5-8ths wide, that travels over 

 tie upper surface of the guides on the to and fro movement of the 

 camera, a moveable pin on each side fixing it in the place desired. 



