654 Miscellaneous. [Dec. 



1827, vol. I. p. 19.) Assume 100° of Farenheit, for the measure of the heat ex- 

 perienced on the surface of the earth, by the direct influence of the sun's rays. 



It is stated in the work above quoted, that silver melts at 22 degrees of Wedg- 

 wood, and as lam not at present exactly aware, at what degree of heat iron 

 becomes red hot, I will assume that of silver, just going into a state of fusion, 

 instead of it*. 



Silver melts at 22° of Wedgwood, and 22 multiplied by 130 plus 1077, equal 

 3,937° of Farenheit*, therefore, the degrees of heat of the Comet, 2,755,500° 

 divided by 3,937°, or heat of melting silver, will make the heat of the former, 700 

 times greater than that of silver going into a state of fusion. 



(Maclaurin, without investigating the truth of the remark, says, the Comet con- 

 ceived a heat, 2,000 times greater than that of iron almost going into fusion. This 

 must be a mistake, for I find that iron fuses at 158° Wedgwood, = 21,617° Faren- 

 heit, so that, using this as a divisor, instead of 3,937°, we obtain only 127s for the 

 number of times excess of the Comet's heat, over that of iron in a state of 

 fusion). 



For gold under the same circumstances, 32° W. = 5,237° F., at which it melts : 

 therefore 2,755,500° -~- 5,237 = 526 times excess of the Comet's heat over that 

 of gold in a state of fusion. 



Tin melts at 442° F. (Fyfe, vol. II. p. 35,) therefore 2,755,500 -f- 442 =6,234 

 times excess of do. over tin. (But at page 21, vol. I. Fyfe says tin melts at 644 

 F., therefore 2,755.500 -f- 644 = 4,278 times do. do). 



Copper melts at 30° Wedgwood = 4,977° F., therefore 2,755,500 -f- 4,977 = 554 

 times for the excess over copper, in a similar state. 



Lead at 612° F. ; therefore 2,755,500 —■ 612 = 4,502 times of same over lead 

 in fusion. 



I believe Sir Isaac Newton's mode of measuring the quantity of caloric in 

 heated bodies, was, by their rate or time of cooling, to a degree equal to that of 

 the surrounding medium. 



It does not, however, so far as I can see, follow, that the interior, to the very 

 centre of the comet, becomes heated by the sun to so great a degree, as is here 

 indicated, and which affection applies to the surface particularly, for, the time that 

 the Comet is exposed to the sun's rays, its rate of motion being increased in pro- 

 portion to its proximity to the sun, (so as always to describe equal areas in equal 

 times,) would probably be of insufficient duration, for so large a body to conceive 

 to its centre, this immense degree of heat ; for, the comet has, no doubt, its sea- 

 sons, and days and nights, as well as the earth, and much free space, almost void 

 of the sun's heat, or even his light, in which to lose its caloric. 



Since writing the above, I see by Mr. James Prinsep's experiments in the Asia- 

 tic Journal, vol. ii. page 140), that iron heated " uniformly to a glowing red " 

 measured 1609° of temperature, Fahrenheit ; if this be used as a divisor instead 

 of the former denominator, for the melting silver, we shall obtain as follows ■ 

 2,755,500 -f- 1609 = 1712.554 times excess of the Comet's heat over that of red 

 hot iron. 



It is evident, that this amount must fluctuate, in exact proportion to the number 

 of degrees, assumed for the measure of the sun's heat, as felt upon this globe, and 

 which I have taken at 100° ; but it appears that the sun's heat at Montpelier, raised 

 Amonton's thermometer, on one occasion, to the height of boiling water, or 212* 

 Fahrenheit, (see Htjtton's Math. Diet, of 1815, p, 640). This would increase the 

 * Vide Ferguson's Astronomy, of 1790, p. 88. 



