R03 



For temperatures under 800° C it makes 

 evidently no diltcrence lor the adjustment of 

 (hepjrometer, if a monochromatic red p;lass 

 is |)hiced before the ocular, or not. The 

 way, in which the wire of the incandes- 

 cent-lamp and the image of the heated 

 cylinder could be observed after the 

 diaphragm /) was removed, is visible from 

 tig. 2 ; the hot crystal there is indicated by 

 Fig- 2. p^ while d represents the wire of the lamp. 



§ 4. In first instance it was tried to find out, in what way this 

 apparatus would show the properties of an isotropous radiator. 



For the purpose to be as much as possible in analogous conditions 

 as were present in the study of the expected phenomenon, these 

 experiments were made with a turmaline-cylinder, with its flat end 

 cut perpendicularly to the optical axis of the crystal. It could be 

 proved easily, that this crystalsection, which was investigated at tem- 

 peratures ranging from 800° to 1000° C. showed in all directions 

 of vibration the same radiation-temperature: on rotating the nicol iV, 

 the iiitensity of the radiation was the same at every moment. This 

 observation proves also, that no disturbing polarisation-phenomena 

 were caused by the reflection of the light at the prism S; the obser- 

 vations to be described further-on are thus proved to be quite inde- 

 pendent of the presence of this reflecting prism. 



The object appeared, after removal of the nicol ^V, to possess con- 

 siderably lower temperature, than the thermoelement indicated; the 

 differences between 700° and 800^ are about 12° — 16° C, between 

 800° and 900° about 3°— 12° C, between 900° and 1000° about 

 5° 0. The indications of the galvanometer are therefore diminished 

 by these amounts, to find the true temperature of the object. Those 

 lower temperatures are probably partially caused by the fact, that 

 the small, but relatively thick cjjinder was fixed at some distance 

 above the hot junction of the thermoelement, while a considerable 

 heat-conduction took place along the suspension-wires. The turmaline- 

 plate, cut perpendicularly to the optical axis, got soon opaque at a 

 temperature of 900° or J 000° ('. ; the cylinder iiowever, which was 

 cut parallel to this axis, remained transparent at 1000° C. for a 

 long time, so that it was possible to see the hot junction of the 

 thermoelement through it, although only very feebly. Finally however 

 also this section got opaque: the investigations with Haidingkk's di- 

 chroscope e.g., are made all with such an opaque cylinder. Because 



