V. DISCHARGE. 279 



over the grounds of the late Andrew Crosse, and converged into his electrical 

 room, as shown in the stereograph. It was here accumulated in the great 

 Leyden battery of 50 jars, and passed thence by dischargers through the 

 metals, which were burnt into the glass on which the strips were laid. 



Frame No. 2 contains composite strips of copper and iron, gold and tin, 

 and gold, silver, and copper, fused in like manner. 



A photograph of the Leyden battery, with which the experiments were per- 

 formed, accompanies the frames. 



1382. " Thunder House," or model to illustrate the identity 

 of lightning and electricity, and the use of lightning conductors 

 in protecting buildings said to be the first model of the kind, 

 and to have been made by Dr. PRIESTLEY with his own hands. 



Conrad Wm. Coohe, M. Inst. C.E. 



1383. Old Electric Egg (beginning of last century). 



Prince Plesh. 



The great age of the instrument appears both from tradition and from 

 the style of the wooden frame and the nature of the brass work. It is certainly 

 one of the oldest instruments of the kind. 



1384. Apparatus employed by Sir Charles Wheatstone to 

 determine the Velocity and Duration of the Electric Dis- 

 charge. 



Rotating mirror. Spark disc. Early rotating disc with balls 

 and sliding rod. 



Museum of Natural Philosophy, King's College. 



791. Rotating Tube Holder, a contrivance for containing 

 a number of Pfliicker's tubes, and obtaining their spectra suc- 

 cessively without loss of time. John Browning. 



792. Rotating Metal Holder, suggested by Mr. Lockyer, 

 for holding specimens of all the principal metals, and obtaining 

 their spectra successively, or for the purposes of comparison. 



John Browning. 



1385. Riess' Spark Micrometer. F. Rob. Voss, Berlin. 



This is well suited for school use, as it is not very dear, and its action 

 is, in proportion, as good as that of larger machines. 



There are new arrangements in the Leyden jar for raising or turning the 

 needle without shaking the entire instrument (a thing to be avoided). 



1386. Apparatus for testing with Lightning Con- 

 ductors. M. Th. Edelmann, Munich. 



1387. Electrograph, apparatus for the production of electric 

 sand-figures, constructed, from the plan of the exhibitor, by M. Th. 

 Edelmann. Prof. W. von Bezold, Munich. 



This serves for study of the nature of the electric discharge in simple or 

 branched circuits, with the aid of sand figures. The figures exhibited have 

 partly been produced with this apparatus, partly under the air pump, and by 

 means of a caoutchouc solution transferred from the ebonite plate to black 



