$Qt Royal Society of London. 



thor Applies \hU method to Dr HerfchePs expefiments : o'rt 

 the heat of a folar ray tranfiniited through different mediums', 

 atfd the crviclufions are very different from what we fhould 

 art ffrfl fight infer: for inflance, in Dr. Herfehel's 24th ex- 

 periment, the blue glafs : ntercepted one-tenth only of th<: 

 rays of hear, and not one-fourth, as the thermometer firmed 

 to indieate. But the immediate interception mult have I 

 fomewh it o-reater than one-tenth, for n. certain portion 6? 

 heat afiualiv communicated to the glafs mu ft have radiated 

 afrefli towards the thermometer, and contributed to produce 

 ttte temperature obferved ; and accordingly as this circum- 

 ilanee took place in a greater or lefs degree, the' themromctei* 

 muit hive been varioufly and irregularly affected. ■ Of inch 

 £n irregularity almod' every one of the experiments fllows 

 eti-i'Mit marks; ami the apparatus is not minutely enough 

 rihed to furnifh data for calculating its magnitude'. From 

 fhefe principles an experiment of Mr. Picfct on the intercept 

 fion of heat, is reconciled with Dr. Herfehel's experiments. 



]n the fecond part of this paper Mr. Prevoft treats of the 

 fefte&'ion of heat and of cold. He obferves that Bacon fug- 

 ge'fted the inquirv reipecling the concentration of invifible 

 neat By glaffes. Lambert attributed the efle& of the reflec- 

 tion from a common fire to its invifible heat. Mr. de Sauf- 

 fure fuggefted to Mr. Picket to confirm Lambert's fufpiciont 

 by experiment, and the fuccefs is well known. His experi- 

 ment on the reflection of cold Mr. Prevoft has already em- 

 ploved in fupport of the opinion that the equilibrium of heat 

 is not a quicicent equilibrium, or an equilibrium of tenfion, 

 but an equilibrium of motion, where the interchanged of heat 

 on either fid-e are equal ; and this theory has been adopted 

 by profeiTor Pic-let, and by other philosophers. Hence the 

 author endeavours to deduce the law already inferred' from 

 Kicbnann's experiments. Mr? Prevoft obferves that this 

 theory would be equally applicable to the opinion of thofe 

 •who confider heat as confiding in the undulations of an eiaftic 

 medium: although he thinks that opinion liable to many 

 objections, efpeciauv on account of the refiftance which the: 

 motions of the planets imift fufler from it. In a note added 

 bv Dr. Young, who communicated the paper, the aficrtion 

 of Newton is quoted in anfwer to this obje6fion, yet Doctor 

 Younn- confelTes that Newton appears to have calculated er- 

 roneouflv; but he obferves, that if the flighted difficulty of 

 this kijjd fhould occur from aftronomical confederations, it 

 might be avoided bv cenfidering the luminiferous ether as 

 urn-oncer: :ed in the phenomena of cohefion, and then its 

 rarity might be a (Turned as great as we chofe to make it. 

 The Society adjourned to November 4. 



FRENCH 



