WARM STAGE 59 



culated. It is made to clamp on to the stage of the 

 microscope by the screws A A f , and is perforated with 

 a large hole coinciding with the optical axis of the 

 microscope; a short tube B, projecting from one end 

 of the warm stage permits water of the desired temper- 

 ature to be conducted from a reservoir through a length 

 of rubber tubing to the interior of the stage and a 

 similar tube at the other end B' of the stage allows 

 exit to the waste water. By raising the temperature 

 of hanging-drop preparations, etc., placed upon it, 

 above that of the surrounding atmosphere, the warm 

 stage renders possible exact observations on spore 

 germination, hanging-drop cultivations, etc. 



FIG. 52. Warm stage. 



A better form is the electrical hot stage designed by 

 Lorrain Smith; 1 it requires the addition of a lamp 

 resistance and sliding rheostat, also a delicate ammeter 

 reading to .01 of an ampere. It consists of a wooden 

 frame supporting a flat glass bulb with a long neck bent 

 upward at an obtuse angle (Fig. 53). The bulb is 

 filled with liquid paraffin, which rises in the open neck 

 when expanded by heat. The neck also accommo- 

 dates the thermometer. Two coils of manganin wire 

 run in the paraffin at opposite sides of the bulb (out- 

 side the field of vision), coupled to brass terminals on 

 the wooden frame by platinum wire fused into the 

 glass. The resistance of the two coils in series is 



1 Made by Mr. Otto Baumbach, 10, Lime Grove, Manchester. 



