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III. — On a Hot or Cold Stage for the Microscope. 

 By W. H. Symons, F.E.M.S., RC.S. 



{Read Uth December, 1881.) 



This stage consists essentially of a copper or brass box A, Fig. 2, 

 8 cm. long, 5 cm. broad, and 1 • 5 cm. deep ; an open tube F, 

 5 X 2 cm., communicates with the interior, and allows of the 

 expansion of the contents and for filling. In the upper and lower 

 sides of the box are apertures H, for the passage of light, 2 cm. 

 in diameter, the lower covered by a thin glass cover, 2-5 cm. in 

 diameter, and the upper by one which constitutes the working 

 stage, 3-5 cm. in diameter. Both covers are kept in position 



Fig. 2. 



between pairs of vulcanized rubber rings by means of brass plates 

 D, clamped on with screws E, the plates being furnished with 

 apertures slightly smaller than the thin covers. A thin copper 

 pipe B B, 5 mm. in diameter, is carried round the bottom of the 

 inside of the box A, one end being forked, and all three branches 

 furnished with taps. This pipe serves to convey the heating or 

 cooling agent to the water or other liquid contained in the box. 



The temperature is ascertained by means of a thermometer C, 

 having its bulb bent in a circle slightly smaller than the aperture 

 for light ; it is placed in the box with the bulb almost touching the 

 upper thin glass cover. Between the thermometer and the copper 

 pipe is a copper partition, having a number of slots in its base to 

 allow of the circulation of the water. In this way the thermometer 

 is protected from undue heat, and as all water which reaches the 

 upper thin glass must pass it, a very near approximation to the 

 temperature of the object upon the thin glass is obtained, espe- 

 cially if the object is protected from currents of air by a cardboard 

 shade. 



The most convenient heating agent is steam, a small flask 

 100 c.c. capacity will work for over an hour, and the temperature 

 may be varied from normal to 95° G. at pleasure ; steam, however, 

 gives out its latent heat immediately on coming in contact with 

 the tube, and therefore that portion of the box or bath nearest to 

 the supply becomes warm very much sooner than that further 



