I ,309 ] 



Lll. An Inquiry concerning the Velocity of the calorific 

 Rays which proceed from the Sun, with a Flew of ascer- 

 taining the Rate of it experimentally , though it should 

 not he far short of the Velocity of Light, &c. &c. 



JL he author of the following paper sends it with his most 

 respectful compliments to Mr. Tilloch, and refers the pub* 

 lication of it, in his valuable Philosophical Magazine, en- 

 tirely to his convenience. Though it has been but lately 

 drawn up, yet the general view of the subject, and the the- 

 orv of the experiment, were fully explained by the author 

 to' a few of his philosophical friends and correspondents 

 more than a year ago. 



RaxMsgatk, 9, Effingham Place, 

 25 August, 1804. 



TILL of late times, whatever effects were observable in the 

 case of different substances being, for a longer or shorter 

 time, fully exposed, to the influence of the sun, it was held 

 as evident that all such had a necessary dependence upon 

 his rays of light.. The changes produced on vegetable co- 

 lours, the aromatic oil of plants, their acquiring the pro- 

 perty of being combustible, the irritable state of their 

 leaves; and further, certain curious effects on the mineral 

 acids, on manganese, on the oxides of silver* lead, bis- 

 muth, &c; nay even the burning heat of the focus of a lens 

 or speculum. All these changes and effects were con- 

 sidered as in some way or other produced by the action and 

 properties of the sun's light. This conclusion seemed in- 

 disputable ; as derived from the direct information of sense. 

 In this however we meet with a remarkable instance of our 

 being sometimes liable to error, from the limited nature of 

 our faculties, even when pursuing philosophical researches 

 according to the rules of a just and cautious induction. 



It was not then suspected, that in the solar beam were 

 blended other emanations, which, being unrelated to vision, 

 had altogether eluded our notice ; or that the marvellous body 

 of the sun, by those recondite processes in his atmosphere 

 which our telescopes show to be in perpetual activity, 

 might be the great fountain not only of light, but of other 

 radiant principles, subservient also to the ceconomy of na- 

 ture, as established in the planetary system. 



That the sun's radiations are actually so compounded, 

 and richer far than had been thought of, has lately begun to 

 appear by two very interesting discoveries. 



Vol. 19. No. 76. Sept. 1804. Y The 



