158 Intelligence and Miscellaneom Articles. 



40° X 2=80°, the temperature measured by the pyrometer. To 

 convert the degrees of this instrument into degrees of Fahrenheit, 

 we must multiply bv 31-25, or 31;^. Thus, 80°x31| would give 

 2500° of Fahrenheit." And 60° x 31| = 1875°. The multiplier 31-25 

 is the number expressing the specific heat of water as compared with 

 that of platinum, the latter being regarded as 1. 



In order to attain very accurate results by this method, precau- 

 tions similar to those required in determining the specific heat of 

 bodies must be taken ; that is, it is necessary to guard against the 

 dissipation of heat by conduction and radiation. The apparatus 

 used by the author consists of a polished tinned iron vessel, of a 

 cj-lindrical form, 3 inches deep and 2 inches in diameter ; this is 

 placed within a concentric cylinder, separated from the enclosed 

 vessel about i inch. By this means there is but little heat lost during 

 the experiment, either by radiation or conduction. 



At the commencement of the experiments, the author imagined it 

 would be necessary to employ a considerable proportion of water, 

 and therefore took twenty-five times the weight of the platinum ; 

 but he found that the temperature gained by the water, even in 

 cases of very high heats, did not exceed 4° or 5° ; and an error of 

 1°, when converted into degrees of Fahrenheit, amounted to 400°. 

 To obtain results within much narrower limits of error, it became 

 obvious, a much smaller proportion of water should be employed ; 

 and ultimately it was found that double the weight of the platinum 

 was in all cases sufficient. 



There is no appreciable loss of heat from the evaporation of steam 

 when the hot platinum is plunged into the water ; — there is probably 

 no actual contact with the water until the platinum is fairly at the 

 bottom of the water. It is in fact the converse of dropping water 

 on a plate of platinum or iron strongly heated ; in which case the 

 water, instead of being suddenly dissipated as steam, assumes the 

 spheroidal form, and runs about over the plate without coming in 

 contact with the heated surfacfe. It is only when the temperature 

 of the metal becomes much reduced that the water is rapidly con- 

 verted into vapour. 



In ascertaining temperatures by this pyrometer, a correction has 

 to be made for the portion of the total heat that is absorbed by 

 1st, the mercury of the thermometer in the water -, 

 2nd, the glass bulb and stem of the thermometer; 

 3rd, the iron vessel containing the water ; 

 4th, the heat retained by the piece of platinum. 

 The portion of the total heat that is absorbed by these several 

 bodies, compared to the portion received by the water, will be in 

 proportion to their several weights, and the specific heat of each com- 

 pared with water. 



Equivalent grs. 

 of water. 

 Mercury... 200 grains X ^th specific heat= 7 



Glass 35 „ X ith „ 6 



Iron 658 „ X ^jth „ 73 



Platinum... 1000 „ X ^V"^ " 31 



Total 117 



