V. DISCHARGE. 321 



1372a. Adjustable Disc Condenser, which has also been 

 used as a spark micrometer. Sir William Thomson. 



It was in this instrument that the sound produced in an air condenser by a 

 sudden change of potential was first heard. The lower part of the cell is 

 arranged to hold cups of pumice-stone impregnated with sulphuric acid. 



1372b. Cylindrical Condenser, for measuring capacity in 

 absolute electrostatic units, described in Messrs. Gibson and Bar- 

 clay's paper in the Transactions of the Koyal Society for 1871. 



Sir William Thomson. 



1372c. Condenser for the Holtz-Bertsch Electrical 

 Machine. Mottcrshead fy Co., Manchester. 



IV. APPARATUS FOR PRODUCING AND OBSERVING 

 EFFECTS OF ACCUMULATED ELECTRICITY. 



1373. Apparatus for demonstrating the fundamental laws of 

 electrical and magnetical attraction and repulsion, made according 

 to the instructions of Professor Ed. Hagenbach-Bischoff, in Basle. 



G. Linder, Basle. 



The ebonite rods are negatively electrified when rubbed -with fur, and 

 positively electrified when rubbed with gun-cotton. (5ee Carl, Repertorium 

 der Experimental-Physik, VIII., p. 75.) 



1374. Insulated Pith-Ball Stand, with mahogany arm ; 

 the arm is itself a box in which the pith balls may be placed when 

 it is not in use. The Council of King's College, London. 



1648. Series of Elder Pith Figures, Butterflies, &c. 



Warmbrunn, Quilitz, and Co., Berlin. 



V. APPARATUS FOR PRODUCING AND OBSERVING 

 EFFECTS OF THE DISCHARGE OF ACCUMULA- 

 TED ELECTRICITY, WITH SPECIMENS OF PER- 

 MANENT RESULTS PRODUCED. 



1375. Photographs of Sparks from a Holtz Machine, in 



cold and in heated air. (See Trans. R. S. Edin., 1874-5.) Taken 

 by an instantaneous process, a quartz lens being employed. 



Prof. Tait. 

 1375b. Spark Micrometer after Riess. 



Warmbrunn, Quilitz, $ Co., Berlin. 



1376. Apparatus used by M. Rijke to measure the distances 

 at which the spark of the Ley den jar passes. 



Prof. Dr. P. L. Rijke, Leyden. 

 40075. X 



