166 



Dr. M. Maclean. On the Effects of 



ments to measure the thermo-electric effect is shown diagrammatically 

 in fig. 1. One junction of the wires was kept in a glycerine bath 

 which could be heated by a Bunsen burner. This junction was tied 

 by a fine copper wire to the bulb of a thermometer T. The other 

 ends of the wires were joined to short copper wires, which served as 

 terminals of the low resistance galvanometer used in the experiments. 

 These junctions were wrapped in paraffin paper or cotton wool, which 

 contained the bulb of a thermometer T' reading half degrees from 

 0° C. to 25° C. A paper screen S was hanging vertically between the 

 Bunsen burner and the thermometer T' and the galvanometer, to pre- 

 vent any heat from the flame reaching the rest of the circuit by 

 radiation. These precautions were taken to make certain that all 

 junctions, except the hot junction, would be at the same temperature. 

 The sensitiveness of the galvanometer was 0*09 mikroampere per 

 division, and as its resistance was 1*5 ohms, the electromotive force at 

 its terminals was 0*135 mikrovolt per scale division. 



§ 2. The metals for which results were given in Part I were copper 

 (six specimens), lead (two specimens), platinoid, german silver, reostene, 

 and manganin.* 



The present paper gives the results of similar experiments made on 

 specimens of commercial! and pure lead, obtained from Messrs. 

 Johnson and Matthey ; and specimens of annealed steel, of aluminium 

 and of nickel. 



§ 3. The method of experimenting was to take a piece of the wire and 

 draw it through a few holes of a draw-plate, so as to reduce its cross 

 sectional area to about a quarter. Then two pieces of the wire, one 

 drawn and one undrawn, each 60 cm. long, were joined as in fig. 1. 

 The glycerine bath was very slowly heated by the Bunsen burner. 

 When there was a rise of temperature of 5° C. the Bunsen burner was 

 drawn slightly aside, so as to give as much heat to the glycerine bath 

 as it lost by radiation. When both the thermometer reading and the 

 spot of light on the scale were seen to be steady, the readings were 

 noted. The circuit was then broken and readings taken of the gal- 

 vanometer zero and the thermometer T'. The circuit was again com- 



* Dr. Anderson, Chemical Laboratory, the University, Grlasgow, gave me the 

 following analyses for reostene and for manganin : — 



Reostene. 



Si 0*61 per cent. 



Fe 79-95 



Ni 16-53 



Mn 1-21 





Manganin. 



Sn .. ., 





Fe .... 



0-6 







Mn .. , 





Ni . . . . 



3-261 „ 



Total.... 98-30 



Total.... 98-585 



t Dr. Anderson pnalysedthe commercial lead and found it contained 99"12 per 

 •cent, of lead. 



