WRIGHT: A NEW THERMAL MICROSCOPE 



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of two distinct parts: (1) a petrographic microscope equipped 

 with a suitable device for simultaneous rotation of the nicols, 

 either by means of gear wheels connected by a bar (fig. la) or by 

 means of a direct connecting bar (fig. lb), the second method be- 

 ing the more accurate and satisfactory; (2) an electric resistance 

 furnace A (fig. 2) which is enclosed within the water jacket W 

 (fig. 2). The details of construction of this furnace are shown in 

 vertical section in figure 2. The furnace consists of two alundum 



Fig. 2 



tubes made especiall}^ for the purpose and wound on the outside, 

 in helical grooves of 1 mm. pitch, with platinum wire 0.35 mm. 

 in diameter. It is then coated with alundum cement and finally 

 baked at 1200° to 1400° for several hours. In this furnace the 

 relatively small openings at the ends and the side, the enlarge- 

 ment at the center and the close winding of the heating coil are 

 arranged to insure uniformity of heating in the central space 

 where the crystal plate is heated and its temperature measured. 

 The water jacket consists of a hollow brass cylinder and sep- 

 arate hollow end plates each of which is provided with an intake 

 and outlet E for the circulating water. Into each end plate a 

 plunger P is fitted for wiping away the air bubbles which happen 



