346 EstrcmelyJIow'Fitfioncflciai the 



The ice however was melted, though very Qowljr, at the bottom of the hot water ; attd that 

 cijcumilance alone would have been lufficicnt to have overturned the hypotlicfis rtfpe£ling 

 the propagation of heat in fluids folcly by means of the inteftine motion. This confideia- 

 tion demanded an attentive enquiry into the circumftances of the experiment. One of the 

 mod ftriking among thefe was, that at the end of the firft half-hour, on examining the fur- 

 face of the ice it was fecn that it had been melted, excepting only where it l^d been covered, 

 or as it were fliadowed, by the Hat flips of deal which fecured the ice in its place. It was 

 (ingular that the ice was defended, not only by the underrnoft piece of wood, but by the 

 other, which, lying acrofs the under piece, did not touch the ice any where except at its 

 ends. It was natural to im.-!gine, from this event, that the ice had been melted by radiant 

 heat or calorific rays from the water, and that a portion of thefe had been intercepted by 

 tlie flips of deal. This fiippofition pointed out another courfe of experimental enquiry-. 



Into a cylindrical glafs jar, b\ inches in diameter, and eight inches high, was put a circular 

 cake of ice, as long as could be made to enter the jar, and about 3^ inches thick ; and on the 

 flat and even furface of the ice was placed a circular plate of the thinncfl tin that could be 

 procured, near 65 inches in diameter, or fufliciently large jufl to cover the ice. This plate 

 of tin (which, to prefcrve its form or keep it quite flat, was (Irengthencd by a ftrong wire» 

 which went round it at its circumference) had a circular hole in its centre juft- two inches 

 in diameter ; and it was firmly fixed down on the upper furface of the cake of ice, by 

 means of feveral thin wooden wedges which pafled between Tts circumference nnd the fides 

 of the jar. 



A fecond circular plate 01 tin, with a circular hole in its centre, two Inches In diameter, 

 and in all other refpecls exaclly like that already defcribed, was now placed over the firft, 

 and parallel to it, at the didance of juft one inch, and, like the firft, was firmly fixed in its 

 place by wooden wedges. 



Thefe perforated circular plates being fixed in their places, the jar was placed in a room 

 where Fahrenheit's thermometer Rood at 34°, and ice-cold water was poured into it, till the 

 water juft covered the upper plate ; and then the jar was filled to within half an inch of 

 its brim with boiling water, and, being covered over with a board, was fulTered to remain 

 quite two hours. 



At the end of this time, the water, which was ftill %varm, was poured off, and, the circuiar 

 plate being removed, tlie ice was examined. 



A circular excavation, jult as large as the hole in the tin plate which covered the ice 

 (namely, two inches in diameter), and correfponding with it, perfectly well defined, and 

 about 2-iOths of an Inch deep in the centre, had been made in the ice. 



This was what our author expected to find ; but there was fomething more which he 

 did not expect, and which for fome time he was quite at a lofs to account for. Every part 

 of the furface of the Ice which had been covered by the tin plate appeared to be perfect, level, 

 and fmooth, and fhcwed no figns of its having been melted or diniiniflied, excepting only 

 in one place, where a channel about an inch wide, and a little more than 2-ioths of an 

 inch deep, which fliewed evident marks of having been formed by a ftrcam of warm 

 water, led from the excavation juft mentioned in the centre of the upper part of the cake of 

 ice to its circumference. As the edge or vertical fide of the cake of ice was evidently 

 worn away where this ftream pafliid, there could be Jio doubt with refpeiSt to its dirc£lion. 

 1 h 



