MOKKIS'S OBJECT-HOLDER. — GLASS STAGE-PLATE. 129 



joint in its centre, into the ball of which can be fitted by a tapering 

 stem either a holder for small cardboard disks, or a larger holder 

 suitable for carrying an ordinary slide. By the free play of the 

 ball-and-socket joint in different directions, the object may either 



Fig. 77. 



Morris's Object-Holder. 



be made to rotate, or may be so tilted as to be viewed obliquely or 

 almost laterally. This instrument can, of course, be used only by 

 side-illumination, and in order to turn it to the best account, the 

 objects to be viewed by it must be mounted on special disks ; but 

 it has an advantage over the preceding in being applicable also to 

 objects mounted in ordinary slides. 



96. Glass Stage-Plate.— Every Microscope should be furnished 

 with a piece of Plate-Glass, about 4 in. by li in., to one margin of 

 which a narrow strip of glass is cemented, so as to form a ledge. 

 This is extremely useful, both for laying objects upon (the ledge 

 preventing them from sliding down when the Microscope is in- 

 clined), and for preserving the Stage from injury by the spilling of 

 sea-water or other saline or corrosive liquids, when such are in use. 

 Such a plate not only serves for the examination of transparent,' 

 but also of opaque objects ; the dark back-ground being furnished 

 by the Diaphragm-plate, and the Condensing-lens being so placed 

 as to throw a side-light upon them.— A small addition may be 

 conveniently made to the glass stage-plate, which adapts it for use 

 as a Growing- Slide. A circular aperture of about the diameter 

 of a test-tube is made near one end of the plate (the length of 

 which, for this purpose, had better be not less than 5 inches)', and 

 in this is to be fitted a little cup, formed of the end of a test-tube, 

 about three-quarters of an inch deep, in such a manner that its, 

 rim shall project a little above the surface of the plate. The cup 

 may be closed by an ordinary cork, or (to avoid danger of splitting 

 it) by a disk of glass cemented to a ring of cork which shall 

 embrace the exterior of the tube ; but a small aperture must be 

 left by grinding a notch in the rim of the cup, sufficient to admit 

 the passage of two or three threads of lamp-cotton. The manner 

 in which the ' growing-slide ' is used is this :— Supposing we wish 

 to follow the changes undergone by some minute Alga or Infu- 



K 



