Additional Notes. 491 



FORD suggests, viz. '' that any thing which any insulated 

 body, or system of bodies, can continue to furnish, "without 

 liynitation, cannot be a material substance." Yet the electric 

 fluid is granted, on all hands, to be a distinct substance ; and 

 we know, that this fluid is constantly furnished, without limi- 

 tation, by means of friction. On the whole, the old opinion 

 seems still, with all its difficulties, to stand on firmer ground 

 than any other, and to have by far the greatest number of 

 advocates. 



The doctrine of ;WiW2/ lieaty or that heat resembles light 

 in being propagated in raijs, or right lines, ^Vas, in some mea- 

 sure, known to Mariotte, Lambert, and Scheele, but 

 was more clearly established afterwards by the experiments of 

 Saussure, PicTET, and Count Rumford; and, finally, 

 the laws of this propagation were more fully developed anij 

 laid down by Dr. Herschell, in his celebrated experiments 

 on light and heat before mentioned. 



Count RuMFORD concluded, from his experiments, that 

 fluids do not conduct heat ; but he ascribes to them what he 

 denominates a carrying power: in other words, he supposes, 

 that in heating fluids, each particle must come in succession 

 to the source of heat, and receive its portion, but that among 

 the particles themselves all interchange and communication 

 of heat is impossible. The experiments by which he consi- 

 ders himself as having established this point are certainly strik- 

 ing, and their results highly curious; but the justness of his 

 conclusions has been called in question, and philosophers do 

 not seem to view his decision as absolute and final. Further 

 experiments must decide the controversy. 



" Dr. M*Clurg, of our city (Williamsburg), was edu- 

 cated at this college. After completing the usual course here, 

 he studied physic at Edinburgh ; was a favourite pupil of the 

 celebrated Black ; and gained much applause by his treatise, 

 De Galore. Indeed, I have lately seen in the Annates de 

 Chemie, I think, for the year 1800, the confession that Dr. 

 M'Clurg first started the idea concerning heat, which the 

 French philosophers have since pursued widi so much success." 

 —MS. Letter from the Rev. Dr. Madison to the Author. 



Frigorific Mixtures, p. 94. 



The first person who made experiments on freezing wix- 

 kives, was M. Fahrenheit, of Amsterdam, at an carlv pe 



