Mr. J. J. Waterston on Solar Radiation. 501 



in which c log 2 = 294, or to reduce to seconds, 



clog2=294x^ 



1 £ 



and c— 756*1. Let t 1 — t =St J then log - = -• — , in which 



r Q fi r 



yu, = hyp. log of 10; hence 



-.- = & [log -=2-51636]. 



fXi i fJj 



From this we may compute the quantity of heat supplied to a 

 unit of surface by the sun in a unit of time corresponding to any 

 value of r. As an example, suppose r=10° and 67=1 second, 



theno>=i^=0°-030453, or 3°«0453 in 100 seconds, is the 

 c 



rate at which the sun communicates heat to a thermometer whose 

 bulb is a sphere 0'42 inch in diameter, when r=10°. 



Suppose the glass of the bulb to be j^th of an inch thick, 

 there would be -0108 cubic inch glass and '0287 cubic inch 

 mercury heated 3 o, 045 in 100 seconds. If r = 20°, the same 

 heating would take place in 50 seconds, and so on. 



To reduce this to thickness of ice melted in 1 minute, we have 



Specific heat of mercury '033, and of glass *l/7. 



Specific gravity of mercury 13*5, and of glass 2*9. 



•0108 cubic inch glass equal in weight to *0313 cubic inch water. 



•0287 cubic inch mercury equal in weight to *387 cubic inch water. 



*010S cubic inch glass raised 3 o, 045 takes as much heat as "0313 cubic 

 inch water raised o, 54. 



•0287 cubic inch mercury raised 3 o, 045 takes as much heat as *387 cubic 

 inch water raised 0°*101. 



•0313 cubic inch water raised o, 54 takes as much heat as is required to 

 raise 1 cubic inch o, 01G9. 



•387 cubic inch water raised o, 101 takes as much heat as is required to 

 raise 1 cubic inch 0°* 0391. 



The entire bulb of the thermometer thus raised 3°*045 is thus 

 equal to 1 cubic inch of water raised •0169-h , 0391=0°-056. 



Now the transverse section of bulb is 0*138 square inch; and 

 since specific gravity of ice is 0*93, and it requires 140° to melt 

 ice, we have 140 x 0*738 x 0-93 x <2?=3*045 ; hence ^ = 0*00312 

 inch, the thickness of ice melted by the sun in 100 seconds, 

 when r = 10°. This is equivalent to 0*001872 inch in 1 minute. 



