434 REPORT — 1869. 



Particulars of Ammunition for Wliitworth Guns, from 5-5-in. to 13-in. bore. 



Mr. Whitworth's patent cartridge increases the range from 15 to 20 per cent. 



Report of the Committee on Standards of Electrical Resistance. 



[Plate YI.] 



The Committee consists of Professor Williamson, Professor Sir C. Wheatstone, 

 Professor Sir "W. Thomson, Professor W. A. Miller, Dr. A. Matthiessen, 

 Mr. Fleeming Jenkin, Sir Charles Bright, Professor MaxweU, Mr, C. 

 "W. Siemens, Mr. Balfour Stewart, Mr. C. F. Yarley, Professor G. C. 

 Foster, Mr. Latimer Clark, Mr. D. Forbes, Mr. Charles Hockin, and 

 Dr. Joule. 



The Electrical Standard Committee have this year had comparatively few 

 meetings, and the re.sults of the experiments made by the individual Mem- 

 bers do not call for a Report of any length. It is, however, thought desi- 

 rable to print at once, as Appendices, the important results obtained by 

 Professor Clerk Maxwell, in determining the ratio of the electromagnetic 

 and electrostatic series of units, and also a description of Sir Wm. Thom- 

 son's experiments on the same subject. 



Description of Sir Wm. Thomson's Experiments made for the Determination 

 of V, the Number of Electrostatic Units in the Electromagnetic Unit, By 

 W. F. KiXG. 



The two principal pieces of apparatus used in these experiments were the 

 absolute electrometer and the electrodynamometer. The former of these in- 

 struments was described at the last Meeting of the Association, and a 

 description of it is printed in the Report. The annexed Plate Ulustxates the 

 arrangements described in what fnllows. 



The electrodynamometer consists of two large coils of fine copper wire, 

 and a smaller coil of still finer wire. The two large coils are about 30 

 centims. diameter, and are placed vertical, in planes parallel to one another; 

 the distance between the large coils is 1-5 centims. (equal to their radius). The 

 smaller coU is suspended between the large coils by a copper wire of such a 



