SSG THIRD REPORT — 1833. 



wires + to silver, though the latter generally stands highest in 

 the tables. Platinum is a worse conductor, and a stronger 

 thermo-negative, than copper : both properties cooperate to 

 lower it in the table, and it falls considerably. 



Platinum conducts a little better than tin, but is much more 

 thermo-negative. The latter quality being predominant, tin 

 stands above platinum in the thermo-electric table. 



Lead conducts worse than either of those metals, but has 

 much less thermo-negative quality ; hence they both range 

 below it in thermo-electric reaction. 



Zinc has a peculiarity deserving the notice of experimenters 

 on this subject: 



Above 250* it is thermo-positive. 

 Below 200° it is thermo-negative. 



And two bars — one heated to about 230°, the other-at the 

 atmospheric temperature (say 60°) — have no reaction on the 

 needle ; that is, there is between 200° and 250° a neutral point. 

 The investigation of this thermo-electric change, at such ma- 

 nageable temperatures, seems to offer an opening to new and 

 advanced ground. Zinc becomes ductile at about 250°. 



6. That the currents in masses of bismuth cannot be easily 

 drawn out by better conductors, and do not seem analogous to 

 currents in the same or other metals acting in pairs : — 



7. That foreign metals brought into contact with a homoge- 

 neous circuit, near a heated point, enter into the thermo-electric 

 communication, and determine a current conformably to their 

 position in the table. 



On some new Phcenomena of Electrical Attraction. By 

 W. Snow Harris, F.R.S. %c. 



The author exhibited and explained to the Section the con- 

 struction and use of some new electx'ical instruments, by which 

 he has been enabled to investigate more rigorously than has 

 been hitherto done the phaenomena of electrical attraction. 

 These instruments consist of an electroscope, an electrometer, 

 a tinit o{ measure, and an adaptation of the common balance to 

 the measurement of electrical force. 



The electroscope acts on the principle of divergence, and con- 

 sists of a long index of reed, easily moveable on a delicate axis 

 set on points in an elliptical ring of brass. This index diverges 

 over a graduated circle from two fixed arms of brass when a 

 slight degree of electricity is communicated to the ring. 



The electrometer measures the force of electrical attraction, 

 under given conditions, by means of two opposed conductors. 



