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The effect of a magnetic field on relative gravity determinations with invar pendulums

Published online by Cambridge University Press:  24 October 2008

E. C. Bullard
E. C. Bullard
Affiliation:
Clare College (Department of Geodesy and Geophysics, Cambridge.)
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Extract

The effect of changes in magnetic moment and in the earth's field on the period of invar pendulums used for relative gravity determinations is discussed, and methods of eliminating them by the use of Mumetal screens are described.

Type
Research Article
Information
Mathematical Proceedings of the Cambridge Philosophical Society , Volume 29 , Issue 2 , May 1933 , pp. 288 - 296
Copyright
Copyright © Cambridge Philosophical Society 1933

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References

* Invar is an alloy of Fe and Ni containing about 36 % of Ni. It is ferromagnetic with an initial permeability of about 2000 (Int. Crit. Tables, vol. 6, pp. 395 and 397). See Guillaume, , Proc. Phys. Soc. vol. 32, p. 374, 1919Google Scholar, for an account of its properties.

† SirLenox-Conyngham, G. P., Geog. Journ. vol. 73, p. 326, 1929.CrossRefGoogle Scholar

‡ This simple magnetometer has proved very satisfactory for measuring the small deflections involved (usually a few minutes of are).

* Z is taken positive when the field is directed downwards, and M 0 positive when the bob is a North Pole.

* A similar result has been obtained by Meisser, , Martin, , and Gengler, , Ger. Béi. f. Geophys., Ergzbd., Heft 2, p. 131, 1932.Google Scholar

* The pendulum has to be left for 2 hours after handling, to attain temperature equilibrium. It therefore takes at least 3 hours to get a point on Fig. 5.

* A steel containing about 78 % Ni, having a permeability up to 80,000.

* In course of publication.

† They are similar to the “electrostatic control” in the quadrant electrometer. Beattie, , The Electrician, vol. 65, p. 729, 1910.Google Scholar