ON A NEW MKTHOD OV CALTBRATINGj &C. 



843 



drawii down to a small size (diameter about 0,01 cm.) aud a thermo- 

 eleraeut is formed by cutting ])ieces of tlie ])latinuin wire, aiid of tlie 



Fig. 5. 



wire of the alloj to be used, about 70 cia. in lengtli and binding 

 thèse to the opposite faces of a recta nguLar block of wood about 1 cm. 

 in thickness. Beyond tliis block the wives project about 3 cm. They 

 are bent toward each other until the free ends are in contact, forming 

 a /', and thèse ends are then fused in the oxyhydrogen flame, forming 

 a junction which is subsequently trimmed down to the form shown in 

 Fig. G. Tliis ligure shows the completed junction 

 as it appears under the microscope. The apex 

 of the / is eut away until the arch of fused métal 

 joining the twowires is considerably less in thick- 

 ness than the diameter of the wires themselves; 

 the face of the junction forming a smooth plane 

 surface. 



The formation of such a junction becomes, 

 with practice, a simple matter and can be performed, as it is necessary 

 to do after each observation, in a few moments. The junction is rigidly 

 mounted u])on the steel bar with the plane passing through the wires of 

 the / vertical and the plane surface of the métal which forms the 

 face of the junction parallel to the ilat face of the acétylène Hame. 

 To the free ends of the wires are soldered the co])per terminais of the 

 galvanometer circuit and the junctions are placed in a bath of melting 

 ice. The support carrying the thermo-eleraent is mounted in such a 

 position as to bring the face of the hot junction as nearly as possible 

 into the center of the field of view of the caméra where it is clearly 

 visible under the illumination of the acétylène flarae; which should, 

 at the beginning of the opération, be about 1 cm. from the junction. 



Fiï. <3. 



