i885.] 



NEW-YORK MICROSCOPICAL SOCIETY. 



from the sub-stage lamp runs along the jointed arm /, then be- 

 hind the stand and by the side of the stage to c, and thence it 

 accompanies the first wire. Besides these there is a third wire, 

 also insulated, and passing downward, which is attached to the 

 stage. Between c and r the three are bound together in one 

 bundle. The communication between the binding-screw at p 

 and the lower end of one or other of the three wires entering 

 the box at the orifice r, takes place through an important sub- 

 sidiary apparatus, the rheostat, and is regulated by means of the 

 switches g and /. The switch / and the spiral German-silver 

 wires, v i h, constitute the rheostat, by means of which the elec- 

 tric current can be strengthened or weakened at pleasure. The 

 wires have different diameters, and thus oppose to the current 



3. 



different degrees of resistance. If a small battery of two ele- 

 ments be used, the rheostat is superfluous. But if a powerful 

 battery be employed, the current will, unless subdued, be too 

 strong for the lamps and will destroy them. 



' The operator begins work by sliding the switch g to the 

 proper point. He will move it to the knob I if he wish to use 

 the upper lamp, to the knob II if the lower, and to the knob 

 III if he desire the current to traverse the stage {B) alone. 

 Next, to adjust the current to the size of the lamp, the power 

 of the objective, and the character of the object under investi- 

 gation, he will first place the switch /"on knob i, and then will 

 cautiously slide it to knobs 2, 3, 4, etc., until the required de- 

 gree of illumination is obtained.' 



Dr. Stein next gives the construction of what he would call 

 an " Electrically-heated Stage." Between the two plates of the 



