302 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



required fur those who wish to pursue the above studies. Ordinary 

 heating stages possess other inconveniences. They take too long in 

 heating and cooling down, and the adjacent parts of the objective are 

 sensibly heated, with consequent risk of damage to the optical parts. 

 The author has endeavoured to meet all these difficulties, and has used 

 his apparatus with satisfactory results for about two years. His stage is 

 shown in fig. 80, which is about half size. He claims for his design 

 the following advantages :— 1. Applicability to every Microscope. 

 2. In spite of the insertion of an inevitably special heating stage, the 

 preparation and condenser are a very small distance apart. 3. Analyzer, 

 objective, object, spiral, condenser, and polarizer, fit together and are 

 combined very compactly on the optic axis. 4. The effect is attained 

 with small quantities of current. 5. The plane-spiral coiling of the 

 incandescent wire guarantees a complete utilization of the heat and con- 

 sequently produces its effect with high efficiency. 6. In spite of the 



y *H# 







f7^!n 



A^Z 



o 



o 



Fig. SO. 



compactness (see 3) of the system, heating of the objective lenses scarcely 

 occurs. 7. It accommodates itself instantaneously to cbanges of resist- 

 ance, as only thin platinum wires are used. 8. Its cost is low. 



The stage is made of vulcanite, 5 or 6 mm. thick, and forms the 

 carrier for the heating wire, the electrical installation, the preparation 

 clamp-springs, and the connecting plugs. The latter are inserted into 

 the holes provided in every Microscope stage. The heating wire is 

 arranged in a round-headed aperture and secured by copper plugs which 

 are passed outwards through tubular apertures, and on their flanged or 

 broadened extremities carry the cable connexions. The heating wire 

 consists of thin platinum about G cm. long and 0*14 to O'lG mm. thick. 

 It takes the form of a flat spiral of about one and a half coils. Before 

 use the spiral should be pressed downwards with thumb and forefinger 

 until about 1 mm. distant from the object carrier, thereby securing that 

 inner and outer winding do not short circuit. The temperature measure- 

 ments were calibrated by observations on the melting of known substances 

 previously embedded between cover-glass and object-glass. An ampere- 

 meter was introduced into the main current, and a voltmeter into the 

 auxiliary current. About five to twenty seconds were required to raise 

 the temperature to 200° C, at which point ordinary cover-glasses cracked. 



