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LVII. On the Precision Measurement of Air Velocity by means- 

 of the Linear Hot- Wire Anemometer. By Louis Vessot 

 King, B.A. {Cantab.), Assistant Professor of Physics, 

 McGill University, Montreal*. 



[Plate X.] 



Section 1. Details or Construction of the Linear 

 Hot- Wire Anemometer. 



IN a paper recently published by the writer f , the theory 

 of the convection of heat from small cylinders cooled by 

 a stream of fluid was extensively studied, the results com- 

 pared with experiment and applied to the development of a 

 precision anemometer intended to be of service in studying 

 complex problems of gas-flow. The special type of instru- 

 ment referred to may be called a " linear anemometer " in 

 contradistinction to several forms of integrating instruments 

 which have already been described \. Detailed specifications 

 are given in the memoir referred to for the construction 

 of this instrument. Use is made of the Kelvin Bridge 



* Communicated bv the Author. 



f Read before the Royal Society of Canada, May 28. 1913. " On the- 

 Convectiun of Heat from Small Cylinders in a Stream of Fluid : Deter- 

 mination of the Convection Constants of Small Platinum Wires, with 

 Applications to Hot-Wire Anemometry," Phil. Trans. Roy. Soc. London, 

 vol. ccxiv. A. pp. 373-432, 1914 ; abstract in the Proceedings of the 

 Roy. Soc. A. vol. xc. 1914, pp. 563-570. 



% Preliminary experiments on the use of a platinum wire heated by an 

 electric current for the measurement of wind-velocity were carried out 

 by G. A. Shakespear, at Birmingham, as early as 1902, but were discon- 

 tinued for lack of facilities in the erection of a suitable whirling table 

 for the calibration of the wires. Electrical anemometry was indepen- 

 dently suggested by A. E. Kennelly in 1909 (A. E. Kennelly. C. A. 

 Wright, and J. S. Van Bylevelt, Trans. A. I. E. E. 28, pp. 363-397, 

 June 1909), and although the actual application to anemometry appears 

 to have been made as early as 1911, the results have only recently been 

 published (A. E. Kennelly and H. S. Sanborn, Proc. of the American 

 Phil. Soc. 8, pp. 55-77, April 24, 1914). Electrical anemometry was 

 also developed independently by U. Bordoni (paper read before the 

 Societa Italiana per il Progresso delle Scienze, Oct. 13, 1911 ; published 

 in the " Nuovo Cimento," series 6, vol. iii. pp. 241-283, April 1912 ; see 

 also 'Electrician,' 70, p. 278, Nov. 22, 1912). and by J. T. Morris (paper 

 read at the British Association, Dundee, Sept. 27, 1912 ; published in 

 the ' Engineer/ Sept. 27, 1912, the ' Electrician,' Oct. 4, 1912, p. 1056, 

 and Nov. 22, 1912, p. 278). A form of integrating hot-wire anemometer 

 has also been described by H. Gerdien {Ber. (lev Deutschen Phys. Ges., 

 Heft 20, 1913). The use of a hot-wire anemometer in the measurement 

 of non-turbulent air currents is described by C. Retschy in a series of 

 short papers published in Bey Motorwagen, vol. xv. March- July, 1912. 



