2334 



Journal of Applied Microscopy 



least one whole turn. As constructed for our paraffine baths the coil is a some- 

 what flexible cylinder, about half an inch in diamater, with copper covering. 

 With its attached insulated wires such a coil is shown hanging on the wall at 

 the left in Fig. 1. The resistance metal used in the coil was a copper-nickel 

 alloy. In the case of the parafBne baths this coil was simply shoved into the 

 bath through an inch hole made in the top of the bath. The knob with con- 

 necting wires protrudes outside, and the coil rests on the floor of the bath, im- 

 mersed, of course, in water. In the case of the thermostats used for incubating 

 purposes, etc., a hole was cut in the side or bottom of the water reservoir, and 

 the coil, after being introduced, was soldered in place so as to close the hole. 



To devise a regulator was more difficult. The use of an ordinary rheostat 

 proved to be impracticable, because it was not possible to make sufficiently fine 



Mg.3 



Mg.2 



Fig. 2. — Diagram to show the connections of heating coil and circuit with relay 

 battery, electro-magnet and meicurial regulator. .J., armature ; i9., bat- 

 tery ; C, heating coil ; J/., electro-magnet ; /'., post in the heating circuit ; 

 R., regulator; .S'., spring; W., wire of the heating circuit; ^V'., wire of the 

 relay circuit. 



Fig. 3. — Upper part of mercurial regulator — Reichert's gas regulator modified 

 — drawn to larger scale than Fig. 2. Pt., platinum wire. 



gradations of resistance for different temperatures, nor by it to provide against 

 fluctuations in the initial current. 



The method finally adopted utilizes a one-cell relay battery to magnetize an 

 electro-magnet. The heating current is made to pass through the armature, 

 which is pulled into contact with a vertical post by means of a delicate spring. 

 When the armature is drawn away from the post by the magnet the heating cur- 

 rent is broken. Into the current of the relay battery is put the regulator ; when 

 the relay circuit is closed at the regulator, the magnet operates on the armature 

 and breaks the heating current; when the relay circuit is broken at the regula- 

 tor, the armature is drawn back by the spring to its first position, thus closing 

 the heating circuit. 



Our Reichert gas regulators {R), already in use for the purpose of regulating 



