: 111 \i M'f 



113 



For heating o'ojects under the microscope, we have long 

 Used a thick copper wire coiled in the flat so as to lie on the 

 stage and with a projecting end which may be heated by a 

 lamp. It is not difficult to adapt a small thermometer so as to 

 indicate very nearly the temperature to which the object is 

 subjected. To regulate the degree of heat employed we pass 

 the end of the wire through a copper tube which is made to act 

 as a chimney to the lamp, and by moving this tube in or out, 

 the coil on which the object lies may be made more or less hot. 



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, 

 with 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 have been made about the year 1856, or even 

 earlier. Thin stages, on the same principle, called Diatom Stages, 

 have been recently introduced by several makers, thus affording 

 another illustration of the aphorism that history repeats itself. 



The same object is also attained by means of the secondary 

 stage, invented by Mr. Lewis Eutherfurd. 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. Rays of great obliquity may thus be passed 

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

 admirable safety 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 advantange of this 

 principle, and so formed the under side of the stage in some of 

 his stands, that the object may be pressed against it by the 



