ON CEUTAIN THERiMOELECTiilC EFFECTS OP STKEri.S IN IRON. 343 



upon the lower part whieli rested lioriz(jiit'i]ly on oliar[) edged ;uip[)ort«. 

 The lower part wa.s somewhat longer than the up[)er ])art, the extra 

 length being a solid cylindrieal piece of iron which during the ex[>eri- 

 nient was sustained at a IjriLZ'ht red heat in a charcoal furnace. To 

 render the fitting secure a ridge cut out longitudinaJIy on each plane 

 surface of the semi-cylindrical lid fitted into a groove cut out on the 

 opposing surface of the lower part. At suitable intervals along this 

 lower part small radial notches were cut. These became IkjIcs when 

 the lid was set in positit^n, and through them wdres were led from the 

 interior of the tube. The wire to be used was stretched alonij' the 

 axial line of the tube ; and it and all the various junction wires were 

 arranged and adjusted l)efore the lid was laid in position. Each junc- 

 tion was a junction of three wires — ( 1 ) the axial wire to be tested, 

 ( 2 ) a tliin wire of the same material, ( 3 ) a thin wire of some (jther 

 metal. The tw(j last formed what we shall call the Thermometric 

 Circuit. Its indications served to measure the temperature of the 

 junction. The circuit, formed Ijy the axial wire and the thin wire of 

 the same materia], was the essential element in the experiment. We 

 shall call it the ThernKjeiectric Circuit. 



The tension was ap[)lied by means of a screw at the extremity of 

 the wire, Avhich projected some distance from the (jpen end of the 

 tube ; and was measured on a spring dynamometer set in line. To 

 ])revent currents of air circulating in the tube, the open cold end was 

 plugged with cotton wo(j], and the side IkjIcs, tlnvjugh which the thin 

 wires came, were filled up with asbestos. The liot end of the tube was 

 closed naturally by the Acrtical face of the solid cylindrical portion 

 îdready menti<jned. The end of the wire was clamped to this face. 



The current were measured on a hiu'li resistance double coiled 

 galvanometer, which was carefully gauged after every single day's 

 experiment. 



