,S06 



§ 6. It needs to be remarked, that from the individual differences 

 in sensitiveness of the human eye, evidently there i-esult greater or 

 smaller values, than those given in column 4, if different observers 

 trv to determine at the same time the apparent temperature-differences 

 between R,„ and the direction perpendicular to it. So one of us 

 always found somewhat qreater values, than the mean value of 

 column 4. Hut the difference itself as a real phenomenon remains without 

 any donbt. 



§ 7. Finally we made also an exjieriment, in which the apparent 

 colder and hotter parts of the turmaline made the impression of being 

 in immediate contact with each other, and therefore could be com- 

 pared immediately, so (hat the phenomenon gets in this way 

 exceedingly striking. 



The funiace was now fixed in a liorizontal |)osition, with its 

 central axis in the direction of the optical axis of the telescope; the 

 total reflecting prism can be removed in this case. Before the objective 

 of the pyrometer, instead of the nicol N, a Haidinger dichroscope- 

 ocular was adjusted in such a way, that two images, an ordinary 

 and an extraordinary one, of a small part of the crystal-surface, 

 were obtained: the object made thei-eforc the impression of being 

 divided into two halves. 



If all the circumstances of the experiment, e.g. the reversing effect of 

 the telescope, etc., were considered, it could be demonstrated, that 

 in the upper field only light was transmitted with a horizontal 

 vibration-plane, in the lower one only that wilii a vertical plane 

 of vibratiou ; the last appeared to be the light of the extraordinary 

 waves. In the fig. 3 these vibration-directions are indicated by the 

 shadowing of the fields. 



The temperature-measurements in both 

 images, — which could be performed in 

 an easy way, because the image of the 

 lampwire, on moving the eye before the 

 ocular, was seen by parataxis now in the 

 upper, now in the lower field, — demon- 

 strated, that at 769^ C. the lower field 

 appeared to have a radiationtemperature of 

 pjg 3 757° C, the upper one however of 769° C. 



In concordance with the well-known fact, that a turmaline-plate, 

 if parallel with the crystallographical axis, principally transmits 

 only the light of the extraordinary waves, which are vibrating in the 

 priiicipal optical section of the crystal, — thus the direction of 



