€- 



VOL. LII.] PHILOSOPHICAL TRANSACTIONS. 60Q 



of which at first he took but very little at a time, and afterwards more in quantity 

 as he could get it down. 



The next day Dr. F. found him much better, when he sat up, talked, and 

 drank some tea, His breathing was easier, but he complained of a short trou- 

 blesome cough and hoarseness ; for which he ordered him a smooth pectoral 

 linctus : and a lenient purging draught was also given him, which had the desired 

 effect. He continued getting better for a day or two, when Dr. F. called on him 

 again, and finding his cough and hoarseness still remain, with a little shortness of 

 breath, he directed him pills of millepedes and gum ammoniac made up with bal. 

 sulph. to be taken twice a day, drinking warm milk after them ; by which means 

 he got perfectly well and went to sea in 1 2 days. 



LXX. A Letter from Benjamin Franklin, LL. D., and F.R.S. Dated Craven- 

 Street, Feb. 4, 1762. p. 456. 



Mr. Canton did me the favour to show me the ingenious experiments he has 

 described in the inclosed letter. They succeeded perfectly as he has related them; 

 and I imagine the communication of them must be agreeable to the curious in this 

 branch of natural knowledge. 



LXXI. A Letter from John Canton, M.A., and F.R.S., to Benjamin Franklin, 

 LL.D. and F.R.S. containing some Remarks on Mr. Delaval's Electrical Ex- 

 periments, p. 457. 



Mr. Delaval, in his curious electrical experiments, found that Portland stone, 

 common tobacco-pipe, &c. would readily conduct the electrical fluid, when very 

 hot, or when quite cold : but were non-conductors in an intermediate state. As 

 no one has yet attempted to account for this, Mr. D. submits the following solu- 

 tion to Mr F.'s judgment 



The stone tobacco-pipe, wood, &c. I apprehend, says Mr. D. conduct when cold, by 

 the moisture they contain in that state ; when their moisture is evaporated by heat, 

 they become non-conductors ; and when they are made very hot, the hot air at, or 

 near their surfaces, will conduct and the bodies appear to be conductors again. 



To prove that hot air will conduct the electrical fluid, let the end of a poker, 

 when red-hot, be brought but for a moment within 3 or 4 inches of a small 

 electrified body, and its electrical power will be almost if not entirely destroyed. 

 And if excited amber, &c. be held within an inch of the flame of a candle, it will 

 lose its electricity before it has acquired a sensible degree of heat.* 



* I have observed also, that the tourrrialin, Brazil topaz, and Brazil emerald, will give much 

 stronger signs of electricity while cooling, after they have been held about a minute within 2 inches of 

 an almost surrounding fire, where the air is a conductor, than they ever will after heating t!.em in 

 boiling water. And if both sides of either of those stones be equally heated, but in a less degree tlian 



VOL. XI. 4 I 



