8 HISTORr of the SOCIETT. 



of the obje(5l of the Dificrtation, and of feme of the reafonings 

 employed in it. 



Da HoTTON was led into the fpeculations contained in the 

 DilTertation, by an account of two experiments made by M M. de 

 Saussi'Re and Pictet of Geneva. In the firft of thefc experi- 

 ments, two concave fpeciila were placed oppofite and parallel to 

 one another, about twelve feet diflant ; and in the focus of one of 

 them was a ball of iron, which had been heated to incandefcence, 

 but allowed to cool till it was no longer luminovis, even in the 

 dark. In the focus of the other fpeculum a thermometer was 

 placed, which prefently rofe 8° (of Reaumur's fcale) above 

 another that ilood near it, but without the focus. Voyages dans 

 les Alpes, torn. II. § 926. 



To account for this phenomenon, M. de Saussure fuppofes, 

 that there exifts what M. Lambert and fome other philofophers 

 have called radiant heat, and that this heat may be obfcure, and 

 not accompanied with light. This radiant heat he conceives to 

 be refle(5led in the fame manner that light is, and by that means 

 to have produced the efFeift on the thermometer that has juft 

 been defcribed. 



To this folution DrHuxTON objedls, alleging, that it afcribes 

 properties or capacities to heat which are inconfiftent altogether 

 with our notion^ of it. We know heat only as a quality of 

 bodies, and as adling either in expanding them, when it is call- 

 ed fenfible heat, or in giving them fluidity, when it is termed la- 

 tent heat. We never perceive it as exifling in any other fhape, 

 and therefore, to fuppofe it capable of moving through fpace, 

 independently of body, and of being refledled from a polilhed 

 furfiice, is to afcribe to heat properties not predicable of it, and 

 quite inconfiftent with its nature, fo far as we have information 

 concerning it. 



Dr Hutton therefore propofes another explanation. From 

 experiments which he had made, long fince, he had found that 



the 



