384 
PEOF. LOUIS VESSOT KING ON THE CONVECTION OF 
and to the more general formulae developed in the preceding sections. It is not 
difficult to understand from a physical point of view that the results of experiments 
on forced convection should be simpler in their interpretation in that the disturbance 
due to the free convection set up by the heated wire may be neglected in comparison 
with the impressed velocity provided the latter be sufficiently large. The first 
experimenter to have shown that the convection loss in a current of air is proportional 
to the temperature difference and to the square root of the velocity seems to have been 
Ser( 22 ), whose measurements on the variation of heat-loss with extent of surface 
indicate approximations to the theoretical formulae. Kennelly’s( 23 ) observations led 
to an empirical formula closely resembling that finally derived in Section 6. 
The experiments of Compan( 24 ) on the cooling of spheres in air currents have 
verified Boussinesq’s approximate equation between comparatively narrow limits of 
temperature and air-velocity. While the present investigation was in progress, the 
work of Morris( 25 ) was published, verifying the application of a formula of the type 
obtained by Boussinesq to the cooling of fine wires heated by an electric current to 
temperatures of about 70° C. above the surrounding air and for air-velocities as high 
as 40 miles an hour. 
The present investigation was undertaken with two purposes in view :— 
(i.) To study the laws of convection of heat from small platinum wires heated by an 
electric current over as wide a range as possible of temperature, air-velocity, and 
diameter in the light of the formulas developed in the preceding sections and to obtain 
in absolute measure the convection constants of such wires. 
(ii.) To make use of the constants thus obtained in the design of accurate and 
portable wind-measuring apparatus to form the basis of a standard system of 
anemometry, as well as to serve for use in a great variety of engineering and 
aerotechnical problems. 
Section 9. Experimental Arrangements. 
(i.) General. 
The general arrangement of apparatus necessary to carry out the requisite 
measurements of heat losses from a series of platinum wires, of diameters 1 to 6 mils, 
consisted of a rotating arm capable of adjustment to any speed as calculated from a 
( 22 ) Ser, ‘ Traits de Physique industrielle,’ t. I., pp. 142-162, 1888. The paper is briefly abstracted by 
Boussinesq, loc. cit., p. 290. 
( 2S ) Kennelly, ‘Trans. A.I.E.E.,’ 28, pp. 363-397, June, 1909. The formula referred to is (28), 
p. 388. 
( 24 ) Compan, ‘ Ann. de Chimie et de Physique,’ 26, p. 488, 1902. 
( 25 ) Morris, “The Electrical Measurement of Wind Velocity,” ‘Electrician,’ October 4, 1912, p. 1056. 
Paper read at the British Association Meeting, Dundee, September, 1912. See also ‘Electrician,’ 
October 4, 1912, p. 1056; ‘Engineer,’ September 27, 1912. 
