434 



RECENT PROGRESS IN PHYSICS. 



Fig. 5: 



Biess gives a des- 

 cription of his instru- 

 ment in several ])la- 

 ces in his memoirs 

 and in Dove's Beper- 

 torium . But tli e d e s~ 

 cription is nowhere 

 perfectly clear and 

 sufficiently illustra- 

 ted by figures. In- 

 deed, it is much 

 to he wished that 

 authors generally 

 would give better 

 drawings of their 

 ap{)aratus, by means 

 of which tedious and 

 yet insufficient des- 

 criptions would be 

 avoided. 



Fig. 53 represents 

 the instrument \ its 

 natural size. The 

 globe which is about 

 3 inches in diameter, 



is perforated in three 



places. The openings at a and h are diametrically opposite each 

 other and are provided with perforated metallic pieces, between which 

 the platinum wire is extended; the third opening c is likewise fur- 

 nished with a metallic fitting, the opening of which is closed by a 

 stopper, so that before the ^perinient the air inside the globe can be 

 put in equilibrium with the external atmosphere. 

 The wire is arranged as shown in figs. 54 and 55. 

 Fig. 54 repre- 

 sents a section of 

 the globe \ the 

 natural size, pass- 

 ing through the 

 middle ofthe open- 

 ings a and h. The 

 fixtures cemented 

 to these openings 

 have holes about 2 

 lines in diameter 

 through which the 

 cylinder / passes. 

 This has a conical 

 cavity on the end 

 towards theinsiue 

 of the globe, into 



