216 Things not generally Known. 



ments with a ball in an ice-pail and a vessel of wire -gauze, into the 

 latter of which is introduced a mouse, which is shown to receive no 

 shock, and not to be frightened at all ; while from the outside of the 

 vessel electric sparks are rapidly produced. This latter demonstration 

 proves that, as the mouse, so men and women, might be safe inside a 

 building with proper conductors while lightning played about the ex- 

 terior. The wire-gauze being turned inside out, the principle is shown 

 to be irreversible in spite of the change what has been the un electrical 

 inside of the vessel being now, when made the outside portion, capable 

 of receiving and ti-ansmitting the power, while the original outside is 

 now unelectrical. 



Repulsion of Bodies. A remarkable and playful experiment, by 

 which the repulsion of bodies similarly electrified is illustrated, consists 

 in placing a basket containing a heap of small pieces of paper on an in- 

 sulated stand, and connecting it with the prime conductor of the electri- 

 cal machine ; when the pieces of paper rise rapidly after each other into 

 the air, and descend on the lecture-tablelike a fall of snow. The effect 

 is greatly increased when a metal disc is substituted for the basket. 



ORIGIN OF THE LEYDEN JAR. 



Muschenbroek and Linnaeus had made various experiments 

 of a strong kind with water and wire. The former, as appears 

 from a letter of his to Reaumur, filled a small bottle with water, 

 and having corked it up, passed a wire through the cork into 

 the bottle. Having rubbed the vessel on the outside and sus- 

 pended it to the electric machine, he was surprised to find that 

 on trying to pull the wire out he was subjected to an awfully 

 severe shock in his joints and his whole body, such as he de- 

 clared he would not suffer again for any experiment. Hence 

 the Leyden jar, which owes its name to the University of Ley- 

 den, with which, we believe, Muschenbroek was connected. 

 Faraday. 



DANGER TO GUNPOWDER MAGAZINES. 



By the illustration of a gas globule, which is ignited from a 

 spark by induction, Mr. Faraday has proved in a most interest- 

 ing manner that the corrugated-iron roofs of some gunpowder- 

 magazines, on the subject of which he had often been consulted 

 by the builders, with a view to the greater safety of these manu- 

 factories, are absolutely dangerous by the laws of induction ; 

 as, by the return of induction, while a storm was discharging 

 itself a mile or two off, a secondary spark might ignite the build- 

 ing. 



ARTIFICIAL CRYSTALS AND MINERALS. " THE CROSSE MITE." 



Among the experimenters on Electricity in our time who 

 have largely contributed to the " Curiosities of Science," An- 

 drew Crosse is entitled to special notice. In his school- days he 

 became greatly attached to the study of electricity ; and on set- 



