OF THE M1CKOSCOPE. 113 



importance that both polarizer and analyzer should be kept 

 stationary, while the object itself rotates between them. 



The stage attached to the New "Working Microscope of Mr. 

 George Wale, and shown separately in Fig. 25, has a novel 

 device for rotating the object. In this case the clips move 

 round the stage. As ordinarily constructed they do not carry the 

 object with them, but it would be easy to effect this by making 

 each clip double, and clasping the object between the two clips. 



The little diatom stage devised by the author, and described 

 and figured in a subsequent paragraph, also affords very simple 

 and convenient means for rotating many kinds of objects. 



Stages for Special Purposes. It may be safely asserted 

 that there has never yet been constructed a stage which would 

 suit the requirements of every worker with the microscope. 

 Indeed, each investigator seems to require special modifications 

 of his own. Thus, it will be found that the ordinary stage, 

 Avith all its appurtenances, is too thick to admit the use of that 

 very oblique illumination which is required by the worker on 

 diatoms, while if the stage be made thin enough it loses the 

 necessary rigidity. Some makers have sought to obviate this 

 by supplying two stages a stout one for common work, and a 

 thin one for diatoms. A microscope now in our possession is 

 furnished with an extra thin stage, which, by a very simple 

 and ingenious device, can be instantly substituted for the heavy 

 one. The microscope is said to have been made by Spencer or 

 Tolles, and must be over twenty years old. Thin stages, on 

 the same principle, called Diatom Stages, have been recently 

 introduced by several makers, thus affording another illustra- 

 tion of the aphorism that history repeats itself. 



The same object is also attained by means of the secondary 

 stage, invented by Mr. Lewis Kutherfurd. This is simply a 

 skeleton stage, which is placed on the ordinary stage, -and is 

 raised so far above it that the illumination may be applied 

 between them. Kays of great obliquity may thus be passed 

 through the object. Rutherfurd's skeleton stage forms also an 

 admirable safely stage, since the object, being held against the 

 under side of the skeleton stage, yields to the slightest pressure 

 of the objective. Mr. Spencer has also taken advantage of this 



