452 MAGNETIC EFFECTS OF 



plied with every turn of the wire ; so that when 

 a magnetic needle is suspended in the middle of 

 the hank of wire, it is placed at right angles to 

 it. In this way the power of the multiplier was 

 made to detect, not only minute portions of elec- 

 tricity that could not be otherwise appreciated, 

 but the smallest changes of temperature, as be- 

 fore observed.* 



By an improvement of this important instru- 

 ment, MM. Nobili and Melloni were enabled to 

 detect the heat of phosphorescent wood, dead 

 fish, living insects, and that of the different co- 

 loured rays of the solar spectrum. But it was pre- 

 viously discovered by Dr. Seebeck of Berlin, that 

 when a circuit is formed by soldering together 

 two metals, and applying the heat of a lamp to 

 one of the junctions, a needle placed within it 

 was deflected from the magnetic meridian, and 

 placed at right angles to the metals forming the 

 circuit. It was afterwards found by Dobereiner, 

 that the heat of the hand was sufficient to cause 

 a deflection of the needle, when applied to the 

 junction of the two metals and by others, that 

 the same effect was produced by applying ice, 

 aether, or any thing which alters the tempera- 

 ture in one part of the circuit from that of the 



* It was also by wrapping a piece of soft iron, bent in the 

 form of a horse shoe, with insulated copper wire, and connecting 

 its extremities with the poles of a galvanic battery, that Pro- 

 fessor Moll of Utrecht was enabled to convert it into a tem- 

 porary magnet of great power. 



