208 Things not generally Known. 



he recognised the phenomena of repulsion, which subsequently 

 led to the establishment of the laws of the sphere of action and 

 of the distribution of electricity. He heard the first sound, and 

 saw the first light, in artificially -produced electricity. In an ex- 

 periment instituted by Newton in 1675, the first traces of an 

 electric charge in a rubbed plate of glass were seen. 



TEMPERATURE AND ELECTRICITY. 



Professor Tyndall has shown that all variations of tempera- 

 ture, in metals at least, excite electricity. When the wires of 

 a galvanometer are brought in contact with the two ends of a 

 heated poker, the prompt deflection of the galvanometer-needle 

 indicates that a current of electricity has been sent through 

 the instrument. Even the two ends of a spoon, one of which 

 has been dipped in hot water, serve to develop an electric 

 current. ; and in cutting a hot beefsteak with a steel knife and 

 a silver fork there is an excitement of electricity. The mere 

 heat of the finger is sufficient to cause the deflection of the 

 galvanometer ; and when ice is applied to the part that has 

 been previously warmed, the galvanometer-needle is deflected 

 in the contrary direction. A small instrument invented by 

 Melloni is so extremely sensitive of the action of heat, that 

 electricity is excited when the hand is held six inches from it. 



VAST ARRANGEMENT OF ELECTRICITY. 



Professor Faraday has shown that the Electricity which de- 

 composes, and that which is evolved in the decomposition of, 

 a certain quantity of matter, are alike. What an enormous 

 quantity of electricity, therefore, is required for the decompo- 

 sition of a single grain of water ! It must be in quantity suf- 

 ficient to sustain a platinum wire r^th of an inch in thickness 

 red-hot in contact with the air for three minutes and three- 

 quarters. It would appear that 800,000 charges of a Leyden 

 battery, charged by thirty turns of a very large and powerful 

 plate-machine in full action, are necessary to supply electricity 

 sufficient to decompose a single grain of water, or to equal the 

 quantity of electricity which is naturally associated with the 

 elements of that grain of water, endowing them with their mu- 

 tual chemical affinity. Now the above quantity of electricity, 

 if passed at once through the head of a rat or a cat, would kill 

 it as by a flash of lightning. The quantity is, indeed, equal to 

 that which is developed from a charged thunder- cloud. 



DECOMPOSITION OF WATER BY ELECTRICITY. 



Professor Andrews, by an ingenious arrangement, is enabled 

 to show that water is decomposed by the common machine; 



