102 



Dr. Shettle. Investigation 



[May 29, 



These integrals are given in the first three cases, and the formula for 

 finding the last, which is somewhat complicated, furnished. 



Finally, it is shown that the results may be transferred to the case of 

 a planetary ellipsoid by changing, in the formula?, e into — e. 



II. " On a New Method of Investigating the Magnetic Lines of 

 Force in Magnets, demonstrating the Obliquity of the 

 Equator and Axis of Bar Magnets." By Richard C. 

 Shettle, M.D. Communicated by Dr. Royston-Pigott. 

 F.R.S. Received April 24, 1879. 



It was not until some thousand observations had been made in the 

 manner about to be described, that I was rewarded with the discovery 

 of the obliquity of the bar magnetic equator, which is the subject of 

 the present communication. 



On a former occasion the Royal Society did me the honour of 

 accepting a similar research on the magnetic condition of arterial and 

 venous blood. 



My present object is to detail the manner in which I have been led 

 up to the result now obtained. 



It appeared to me that the usual method of displaying magnetic 

 currents by means of the curves assumed by steel filings were only 

 rough approximations. 



Long after I had been occupied with these observations I became 

 aware, through the kindness of Professor Stokes, Secretary to the Royal 

 Society, that Sir George Airy, the Astronomer Royal, had in a short 

 paper in the " Transactions," investigated (with a pocket compass fur- 

 nished with a magnetic inch-needle) these lines of force. The method 

 which I have adopted is essentially different, and greatly exceeds in 

 delicacy. 



1st. — Inch magnetized steel needles were suspended and nicely balanced 

 on a single silk fibre 6 inches long. 



These needles carried over the magnets assumed rapidly changing 

 positions, and readily demonstrated, as in the paper alluded to, the 

 varying force and direction as usually portrayed in treatises on mag- 

 netism. But these long needles utterly failed in the niceties of research 

 on which I was employed. 



2nd. — Needles varying from half an inch to the l-16th of an inch were 

 mounted and suspended, in a similar manner. 



I found the latter thoroughly competent to trace sudden changes in 



