136 N. D. C. Hodges—Size of Molecules. 
requires the use of ‘000825 milligrams of work. The total 
‘superficial area of all the parts, supposing them spherical, will 
e 4zr?N. The number of parts being N, the work done in 
dividing the water will be 4zr?N. For the volume of all the 
parts we have 4zr°N. This volume is in accordance with 
the requirements of the kinetic theory of gases, about ;745 
of the total volume of the steam. The volume of the steam 
is 1752 times the original unit volume of water. 
Hence £N 2r*3000 = 1752 
4N zr*-000825—636°7,423 
One unit of heat equals 423 milligrams. 
Solving these equations for r and N, we get r equal to 
“000000005 centimeter, a quantity of the same order of magni- 
tude as has already been obtained by Thomson, Maxwell and 
others, N equal 9000 (million)?n for the number in one cubic 
centimeter 5 to 6 (million) 
The superficial energy of platinum is 169-4 milligrams per 
Square meter or (1694 per square centimeter, equal to ‘00004 
of a unit of heat. The proposition 
9: 34,462—z2: 00004 f 
gives the weight of water condensed on square centimeter of 
surface or the volume in cubic centimeters as 1, whic 
agrees with the other result. 
Physical Laboratory, Harvard College, May 14, 1879. 
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