802 



lliis tlieniioelement was connected with a sensitive direct-reading; 

 galvanometer G. The fnrnace had an inside- winding of platinum-wire; 

 it was surrounded by a iiollow mantle M, in which continually a 

 stream of cold water was circulating. It was heated with direct 

 current of 220 Volt and 3 — 5 Amperes; the temperature was regulated 

 by means of a rheostate in such a way, as to be kept constant 

 at will at every height. The cylinder was fixed in such position, 

 that it remained at all sides equidistant from the furnace-walls, and that 

 it was situated in the very short part of the furnace, where no consider- 

 able fall of temperature along its axis, could be detected. Above the 

 furnace a movable diaphragm D was present, to make an entrance 

 to the measuring-apparatus possible only foi- the rays, coming from a 

 very small part of (he surface of the glowing cylinder ; a plane-convex 

 lense L, arranged above the furnace, allowed to observe a sharp image of 

 every chosen part of the glowing cylinder-surface, by means of the 

 telescope of the radiationpyrometer P. 



This pyrometer P was of the HoLBORN-KuRLBAUM-type, which is to be 

 preferred to the about equally accurate pyrometer of Wanner, because of 

 its giving an opportunity to obeerve the objects themselves in the hot 

 furnace sufliciently well. Before the objective of the pyrometer, a total- 

 retlecting prism (45°) ;S was fixed, whose hy pot henuse-side was heavily 

 coated with silver; it' was fixed in an innerlyjblackened tube, which at 

 the same time bore the rotating Nicol-prism lY. This prism N could 

 eventually be removed in an easy way, and, if necessary, be substituted 

 by another prism X' , to be fixed this time however at the opposite 

 end of the telescope, before the ocular. The telescope contained the 

 accurately calibrated incandescent-lamp //, which was lighted by 

 the current of two storage-cells A. In the same circuit were pi-esent 

 two easily adjustable rheostates W, and W^, and a milliampère- 

 meter L provided with pointer and scale. 



The calibration of the incandescent-lamp H between 600° and 

 1000° C. gave the following results: 



Temperature in ° C. 



Intensity of current 

 in milli-ampères: 



Number of milli-ampères, 



corresponding with a 

 temperature-rise of 1° C. : 



600° 

 700° 

 800° 

 900° 

 1000° 



318 

 356 

 396 

 440 

 484 



0.38 

 0.40 

 0.44 

 0.44 



