CALORIC AND ELECTRICITY. 451 



vention of this beautiful instrument, a prepared 

 frog was considered the most delicate test of gal- 

 vanic electricity. But it has been found, that 

 the multiplier is not only a far nicer test of elec- 

 tricity, but that it is also the most delicate ther- 

 moscope ever invented that -^fa part of a de- 

 gree of Fahrenheit's thermometer produces a 

 sensible movement of a small needle suspended 

 by a fibre of silk. From which it follows, that 

 magnetic phenomena are not confined to the 

 action of electricity, but also result from the 

 agency of caloric in quantities too small for mea- 

 surement by any other test. 



It is therefore not a little surprising, that when 

 Dr. Faraday offered as a proof, that all the 

 varieties of electricity are essentially the same, 

 because they all produce magnetic effects, that 

 he did not recognize the identity of caloric and 

 electricity. 



Guided by the general fact discovered by 

 (Ersted, that a magnetic needle placed over the 

 wire connecting the poles of a battery in action 

 has a tendency to arrange itself at right angles 

 to the conducting wire, Schweigger covered a 

 common brass wire with silk thread, for the 

 purpose of insulating it. This wire was then 

 lapped round a piece of wood, 50, 100, or 200 

 times. When its two extremities were connected 

 with the poles of a battery in action, the galvanic 

 current passes through all the windings of the 

 wire, by which the magnetic effects are multi- 



