LONDON, EDINBURGH, anp DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. _ 
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I 8.1/7 oat § 
ee ES. AUGLO1900. ae 
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AUGUST 1904. \ PATENT. OFFICEA 
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XIV. The Law of Action between Magnets and its bearing on 
the Determination of the Horizontal Component of the 
Earth's Magnetic Force with Unifilar Magnetometers. By 
Cuartes CHrEE, Se.D., DL.D., F.R.S. (From the 
National Physical Laboratory.)* 
CONTENTS. 
§§ 1-3. Fundamental formule ; P, Q, and R coefficients. 
4-9, Effect of errors in the setting of the deflexion-magnet, or in 
the deflexion distances. 
10-11. Effect of errors in deflexion-angles. 
12-13. Consequences of the neglect of the higher coefficients. 
14-20. Theoretical expressions for the coefficients and their numerical 
evaluation in particular cases. 
21-23. Observational results for coefficients, and evidence of change 
in individual magnets. 
24-25. Departures from the conditions assumed in the ordinary 
theoretical treatment of the deflexion experiment, and their 
consequences. 
26-31. Experiments on the pole-distance in magnets. 
§ 1. W HEN a freely suspended magnet is deflected out 
of the magnetic meridian by a second magnet, 
the two being at right angles to one another in the first 
Lamont’s position, the following relation holds :— 
2m 2 Pol Quik ; 
sae 3 —q—e\ 1+ 2 died + i + ep sinu. (1) 
Here m is the magnetic moment, at 0° C., of the deflecting 
magnet, ~ its temporary induction coefficient, g and q’' its 
* Communicated by the Physical Society : read May 27, 1904. 
Phil. Mag. 8. 6. Vol. 8. No. 44. Aug. 1904. I 
ae RAR Y SS 
