98 Chemical and Physical Notes 



the circular area corresponding to the diameter a by the length 

 of the equivalent cylinder b. The water value of the bulb is 

 d= 0'4$7c. When Table XVI was calculated, 0-457 was use d 

 as the specific heat per unit volume of the bulb, instead of 

 O'475, which was adopted later. It has not been thought 

 necessary to recalculate the table. The area of external 

 surface is the circular area of the diameter, added to the 

 product of the length of the equivalent cylinder and its 

 circumference. The area of axial section is the product of 

 the diameter of the cylinder and its length, and the effective 

 axial area (g) is the axial section multiplied by O'84 ; g is 

 proportional to the quantity of the sun's rays, which strike 

 the bulb in unit of time. The term of cooling, h, is given in 



seconds, and its reciprocal j is the fraction of the excess of 



heat lost per second during cooling. 



In Table XVII five separate observations of the stationary 

 temperature reached by the thermometers side by side are 

 given. The temperature of the air was i5*oC. The excess 

 of heat in each bulb is m = Id, or the water value of the bulb 

 multiplied by the excess of its stationary temperature above 



that of the air. The loss of heat per second n = -r as was 



h 



above described ; / = - is the loss of heat per second referred 



to unit area of effective axial section. It has been pointed 

 out that g, the effective axial area, is the sectional area of the 

 bundle of solar rays which strikes the bulb, and it is therefore 

 proportional to the supply of radiant heat by the sun to the 

 thermometer. But when the temperature of the thermometer 

 in the sun has become stationary it is dissipating the whole of 

 the heat which it is receiving. Now n gives the rate at which 

 it is cooling, in gramme-degrees 1 (gr. C.) per second ; there- 

 fore the bundle of sun's rays of sectional area g is supplying 



1 It is convenient to give compound names to compound units; they then 

 explain themselves. One gramme-degree (i gr. C.) is the heat required to raise 

 the temperature of one gramme of water by one Centigrade degree. Names such 

 as calorie or therm are indefinite, and may be confusing. 



