1884.] 



MICROSCOPICAL JOURNAL. 



223 



regulated by controlling the current. 

 The air, which passes upward through 

 the opening in the stage, is thus 

 heated, and conveys the heat to the 

 object on the slide 

 by convection. 

 For a warm-stage 

 this seems to be 

 the most conveni- 

 ent device yet sug- 

 gested. A metal 

 thermometer can 

 be placed be- 

 tween the heat- 

 ed spiral and 

 the object, so 

 that the tem- 

 perature can be 

 read oft' at an}- 

 moment from 

 the scale ; or 



Fig 3a. Electric Lamp Stand a thcrmo-elec- 



tric arrangement can be applied 

 for the same purpose, a galvanom- 

 eter needle then indicating the 

 temperature. 



In Fig. 33 is shown what seems 

 to be a very convenient applica- 

 tion of electricity for photograph- 

 ing objects. Only one battery-cell 

 is shown, but we infer that two are 

 used in practice. The lamp s is of 

 i^ or 2 Volt's tension, and two such 

 elements will 

 suffice to give 

 it an intense 

 white heat. 

 The lamp can 

 be moved up 

 and down on 

 the mirror-bar, 

 according to 

 the iljumina- 

 tion required. 

 The photo- 

 graphic camera /F; 

 is attach- 

 ed to the 

 micro- 

 scope by 

 the screw 

 c. 

 For low- 



powers, of 20 to 100 diameters, an 

 exposure of 15 to 20 seconds suf- 

 fices when dry plates are used, the 

 correct time being easily learned by 

 experiment. When higher powers 

 are used even 10-12 minutes may be 

 required, and several trials must be 

 made to determine the proper expo- 

 sure. 



The electric light has already been 

 used considerably in microscopy, and, 

 in fact, by a few persons for a number 



33. — Photograpli > 



