FORCES AND ORGANS. 



11 



afterwards remove loop No. 2, the current must traverse the 

 apparatus M, which is an electro-magnetic motor. This appa- 

 ratus will begin to move and will produce mechanical action. 



Let us at the same time remove loop No. 3, the current 

 must also traverse a registering thermometer. [That 

 instrument is constructed as follows. It is a sort of Reiss* 

 thermometer, formed of a spiral of platinum, which the current 

 traverses, and which is conducted into a flask full of air. 

 Under the influence of the heating of the spiral by the current 

 which traverses it, the air in the bottle dilates, and passes, 

 through a long tube, into the registering apparatus. The 

 latter is composed of a drum of metal, closed on the upper 

 side by a membrane of india-rubber. When the air pene- 

 trates into the drum, the membrane swells, and lifts up a 

 registering lever, which traces on a turning cylinder E, a curve 

 whose elevations and depressions correspond with the rise and 

 fall of the temperature.] 



By removing loop No. 4, we force the current to traverse 

 an apparatus L, with carbon points, in which electricity 

 gives birth to the bright light with which every one is 

 acquainted.- When it passes through the voltameter V, the 

 current produces decomposition of the water. The intensity 

 of the current is measured by the quantity of water decom- 

 posed, i.e.f by the volumes of hydrogen and oxygen which 

 are disengaged. 



We see, in the first place, by means of this apparatus, 

 that electricity can become successively mechanical work in the 

 motor M, heat in the spiral of the thermometer T, light 

 between the carbon points L, and chemical action in the 

 voltameter V. 



But we also recognise that the electricity which undergoes 

 one of those metamorphoses is taken away from the current 

 whose energy is thus diminished. If, for example, we make 

 the motor M work, w^e shall see that the register marks a 

 diminution of heat in the thermometer. If we stop the 

 electro- magnetic motor with the hand, an increase in the 

 temperature becomes immediately apparent; the registered 

 curve rises. 



When the electro-magnetic motor is working, we see the 



