192 ON RADIANT HEAT, &C. 



of the primitive form and those of the secondary crystals arc 

 not unfrequent in the varietits of carbonated Hme. 

 Crystals for- From these examplts it is seen, that resuUs. which I had 



^^cry suppos- g-,yjj(j .jg iiifiely hypothetical, appear as descriptions by an- 

 ticipation of so many products of ci ystalhzation, which ex- 

 isted in the bosovn of the Eaith without our knowledare. 



VII. 



Extract of a Letter from Dr. Francis Delaroche to 

 F, Bergeb, Esq.; on Radiant Heat and other Subjects, 

 Communicated by the latter Gentleman. 



In 



Paris, July the nth, 1811. 



FheHoraena 9f J^pif my ]ast two letters, I mentioned to you an inquiry into 

 the phenomena of radiant caloric, which I commenced last 

 spring, and ot which the princi|)al results are the following. 

 Radiant CHioric, almost entirely divested of the faculty of 

 traversing glas.«, when the substance that emits it is at less 

 than 100° [i^l2° F.] or even 180° [366° F.], acquires this 

 property very manilestly, and independent of the light that 

 may accompany it, in proportion as the temperature of the^ 

 heated body is increased beyond this. 



The rays emitted, simultaneously by one and the same 

 heated body differ from each otl^er with respect to the fa- 

 culty of traversing glat^s. 



The quantity of radiant caloric emitted, or, to speak more 

 properly, the quantity of caloric arriving at a distance in the 

 radiant form is not proportional to the temperature of the 

 heated body, as commonly supposed, but it is infinitely 

 greater in proportion at high temperatures, than at lower. 



Lastly, that the law of refrigeration established by New- 

 ton, though nearly accurate at low temperatures, is far from , 

 being so at high ones. 

 Phenomena of Nothing very striking has occurred here in the sciences 

 light. within these few months. Mr. Malus is still pursuing with 



success his inquiries concerning polarised light. Mr. 

 Arago likewise is making some curious experiments on the? 

 inuminationofsamie subject. Some, that he has lately made on the illu- 

 ^•t^f^ mination 



