Dr. Faraday's Experimental Researches in Electricity. 475 



remainder of the very interesting and important experiments -which 

 have been entrusted to me, — that portion of the whole, namely, 

 which relates especially to centrifugal pumps. I liave also to state, 

 that if my engagements permit, I should be desirous of proceeding 

 with a renewed and more extended set of experiments on the fric- 

 tion of discs, with an apparatus depending on the same leading 

 principle as that which I have already used, — a principle which on 

 trial has been found remarkably well suited for the desired purpose. 

 For the attainment of greater accuracy and of a wider range of the 

 experiments, it seems to me that no better method of procedure 

 could be adopted, than to follow the same leading principles, with 

 an apparatus of rather more refined construction, involving such 

 improvements in details as have been suggested by the experience 

 gained in the course of the experiments already made, and for the 

 sake of greater steadiness of motion, worked by steam power instead 

 of the hand of an operator. Should I have it in my power to con- 

 duct this renewed set of experiments, a detailed account of them 

 will be preferable to a detailed account of those already made. 



In respect to the experiments on Centrifugal Pumps, I have to 

 say that I have prepared plans for an experimental apparatus on 

 principles which 1 consider are peculiarly well suited for the attain- 

 ment of useful and accurate results, and that I intend to proceed 

 with the experiments as soon as my engagements shall permit. 



I have further to state, that from the Experimental Fund of £50 

 granted by the Royal Society, the entire outlay as yet incurred has 

 been £6 5s. 9rf,, leaving a balance of £43 14s. Zd. for the more 

 extended experiments yet remaining to be made. 



James Thomson. 



Belfast, Ajiril 13, 1855. 



Nov. 22. — Sir Benjamin Brodie, Bart., V.P., in the Chair. 



The reading of Dr. Faraday's paper, " Experimental Researches in 

 Electricity — Thirtieth Series," was resumed and concluded. 



The following is an abstract : — 



* § 38. Constancy of differential magnecrystalUc force in different 

 media. — That a magnecrystal formed into a sphere (or some equiva- 

 lent shape, so that mere length should have no influence) sets with 

 the same force in the magnetic field, whatever the magnetic nature 

 of the medium around it, has been shown generally, and for a few 

 cases, on former occasions. The author was under the necessity of 

 verifying and enlarging the old results ; and upon employing the 

 following magnecrystals, namely bismuth, tourmaline, carbonate of 

 iron, red ferroprussiate of potassa, and also compressed bismuth, sur- 

 rounded in succession by the following media, — phosphorus, alcohol, 

 oil, camphine, water, air, and saturated solution of protosulphate of 

 iron, he found the result to be the same as before. The mode of 

 estimating the set was as follows : — The selected crystal being sus- 

 pended in the magnetic field by a torsion-wire, right-handed force 

 was then slowly applied by the revolutions of the torsion-liead above, 



* Series XXIX. is published in the Phil. Trans, for 1852, p. 137. 

 212 



