424 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, B.C., 



FIG. 2477. 



FIG. 2481, 



Each. 

 s. d. 



2466 Electrical Mill, showing rotation produced by 



electricity given off from the points of the vane 

 (fig, 2466) . 



2467 Electrical See -Saw, illustrating electrical attraction and 



repulsion (fig. 2467) 



2468 Electrical Inclined Plane, the fly revolving by the 



dispersion of electricity from the points, and ascend- 

 ing the incline (fig, 2469) 



2469 Apparatus for explaining the theory of Thunder Clouds 



(figs. 2469), 



2470 Harris's Thunder Cloud Apparatus, constructed of a light metal 



needle, balanced to turn very freely upon a vertical point con- 

 nected with one coating of a large Leyden jar, or Electric Battery. 

 One end of the needle is covered with light cotton wool, to 

 represent a cloud, which can be arranged to approach either figs. 

 2471, or 2471*, and the discharge takes place ; a very interesting 

 experiment ........... 



2471 Thunder House (Dr. Priestley's), or Obelisk for showing 



the use of lightning conductors in protecting 

 buildings (figs. 2471 and 2471*) 12 6 



2472 Fire House, for illustrating the same fact (fig. 2472) . 



2473 Powder House, for showing the necessity of a continuous 



metallic lightning conductor, which in this experiment 

 is broken in the centre of a cup containing gunpowder. 

 This is ignited and explodes by an electrical discharge, 

 blowing down the house (fig. 2473) .... 



2474 Sturgeon's Apparatus for igniting Gunpowder, Alcohol, 



JEther, &c., by electricity (fig. 2474) .... 



2475 Apparatus for the ignition of Phosphorus, consisting of two 



brass cups, insulated upon glass supports, for holding small 

 pieces of phosphorus ; between these is a stand for a small lamp 

 or candle ; the passage of electricity between the cups will carry 

 the flame towards the phosphorus, and ignite it (fig. 2475) . 



Each. 

 s. d. 



110 



15 



110 



150 



100 



15 



1 4 



1 10 200 



12 6 



14 



