80 FRAGMENTS OF SCIENCE. 



figure as flowing through the wire when the voltaic circuit 

 is complete. 



I have said that no visible change occurs in the wire 

 when the current passes through it. Still a change over 

 and above what you have seen really does take place. Lay 

 hold of those spirals, and you will find them warm. Let 

 me exalt this warmth so as to render it visible to you. In 

 front of the table is a thin platinum wire six feet long. On 

 sending a current from a battery of fifty pairs of plates 

 through this wire it glows, as you see, vividly red. I shorten 

 the wire ; more electricity now flows through it, and its 

 light becomes more intense. It is now bright yellow ; and 

 now it is a dazzling white. This light is so strong that 

 though the w r ire is not much thicker than a bristle, it ap 

 pears to those on the nearest benches as thick as a quill ; 

 Avliile to those at a distance it appears as thick as a man s 

 finger. This effect, which we call irradiation, is always pro 

 duced by a very strong light. It is this same electric cur 

 rent that furnished us with the powerful light employed in 

 one of our first experiments. The lamp then made use of 

 is provided with these coke rods ; and when the electric 

 current passes between them we obtain a light almost as 

 brilliant as that of the sun. 



And now let us return to the point at which the elec 

 tric current was introduced the point, namely, where the 

 tearing asunder of the locked atoms of a chemical com 

 pound was spoken of. The agent by which we effect this 

 is also the electric current; and I hope to make its action 

 visible to you all. Into this small cell, containing water, 

 dip two thin wires. By means of a solar microscope and 

 the powerful light of our electric lamp, a magnified image 

 of this cell is thrown upon the screen before you. You 

 see plainly the images of the wires. And now I send 

 from a second small battery which rests upon this table an 

 electric current from wire to wire. Bubbles of gas rise 



