ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



465 



The lower part of the aperture is closed by a small glass diaphragm, let 

 into a copper ring. On the other side of the large bos is fitted D' Arsonval's 

 caoutchouc regulator ; on the front side is a cylindrical diverticulum like 

 that of a hot filter. On the upper surface are two brass tubes ; to the front 

 one is fixed, by means of a caoutchouc ring, a glass pipe into which the 

 water rises in order to determine the pressure and consequently the regula- 

 tion of the escape of gas ; the other tube, closed by a caoutchouc plug, is 

 that through which the box is filled with water and freed from gas or air. 

 In front another tube passes through the chamber ; in this is inserted a 

 thermometer insulated by means of a piece of Bristol board. On the 

 right side of the smaller box is a lateral opening for the insertion of the 

 slide, and as the upper part of the larger box is wanting towards the right, 



Fig. 107. 



Showing the appearance of the hot stage arranged on the Microscope. A, hot chamber 

 b, water tube ; c, glass pressure tube ; d, D' Arsonval's regulator ; e, heating cylinder ; 

 F, burner with glass chimney ; t, thermometer. 



the defect serves for the easier manipulation of the slide. The hot stage 

 proper is 5 mm. high, 75 mm. long, and 40 mm. broad, and in order not to 

 lose heat a small door drops down just so far as not to interfere with the 

 slide. The gas burner is inclosed in a glass chimney, in order to keep the 

 flame quite steady. 



The apparatus is put in working order as follows : The pressure tube 

 having been arranged, the chamber is filled with boiling water, and is 

 shaken from time to time in order to disengage any inclosed air. The 

 apparatus is then placed on the stage, the gas lighted, and the regulator 

 tap turned down until the flame begins to diminish. The tube is 



