A vacuum anemometer is described for indicating or measuring the streaming of gases and vapors in vacuum. The device is particularly useful for measuring the projective vapor emission from liquid surfaces and the flow of gas through pipes, for instance, between a vessel and a pump. The anemometer consists of a propeller mounted on a shaft supported by jeweled bearings, the propeller being driven by the stream of gas. To measure the speed of the propeller, a small ac generator is incorporated in the device, and the output is indicated by an electronic voltmeter. Under conditions of heavy electrical braking, it is shown that the speed is directly proportional to the pressure, independent of the nature of the gas and of its molecular weight. The instrument is rugged, insensitive to vibration, stable, and readily calibrated. It has low inertia and responds rapidly to a change in the momentum of the stream of incident molecules. Sources of error are discussed and typical performance data are reported.

1.
K. C. D.
Hickman
,
Ind. Eng. Chem.
44
,
1892
(
1952
).
2.
K. C. D.
Hickman
and
D. J.
Trevoy
,
Ind. Eng. Chem.
44
,
1903
(
1952
).
3.
C. A.
Coulomb
,
Mém. Acad. Roy. Sci. Danemark
10
,
161
(
1785
).
4.
F.
Palmer
,
Am. J. Phys.
17
,
327
(
1949
).
5.
J. A.
Van Horn
,
Phys. Today
3
,
6
(
1950
).
6.
E. S.
Perry
and
W. H.
Weber
,
J. Am. Chem. Soc.
71
,
3726
(
1949
).
7.
Bowden
,
Young
, and
Rowe
,
Proc. Roy. Soc. (London)
212A
,
485
(
1952
).
8.
I.
Langmuir
,
Phys. Rev.
8
,
149
(
1916
).
9.
Magnet Manual No. 4 (The Indiana Steel Products Company, 1951), p. 13.
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