ROTATION PRODUCED BY HEAT. 71 



of a person approaching within thirty feet of this 

 instrument, and even of the bodies of insects, of 

 phosphorescent wood, putrifying fish, &c., are de- 

 tected by the motion of the needle, as stated by 

 Nobili and Melloni. 



An ingenious experimenter, Dr. Locke, of 

 Ohio, describes in " Silliman's Journal " a thermo- 

 scope with a current changer affixed thereto for 

 reversing the connections, whereby a needle 

 weighing one and one half ounces was made to 

 revolve by the heat of his finger, by timely rever- 

 sals of the currents. 



It may seem surprising that the use of a lump 

 of ice, instead of a lamp flame, will produce 

 movements of the galvanometer needle. A bat- 

 tery is made (Fig. 14) by applying a frigorific 

 mixture on the bars at A, and a plate of heated 



iron, E, at their lower ends. On the upper 

 ends of the metallic wires, packed together 

 with insulating varnished silk, and inclosed 

 in a curb, B, is placed pounded ice or snow, 

 with some salt representing the polar seas; and 

 beneath the lower extremities of the wires is 



