Dr Traill on Thermo-Magnetism. 261 
and a half helix inversion when the S. end is heated ; in electro- 
magnetism, when the zinc is to the N. of the copper, they are 
connected by a right helix inversion of poles taking place ; while 
the same effect is produced with a left helical connecting piece, 
when the zinc is to the S. of the copper. The result of various 
experiments shewed, 1 5. That the needle is more powerfully 
acted on when it is in the axis of helical connecting pieces, than 
when the connecting pieces are simple slips or wires of metal. 
16. The influence of right helices are the reverse of those of left 
helices in thermo-magnetic, as well as electro-magnetic combina- 
tions. 17. The effects of inclined and vertical helices in thermo- 
magnetic combinations, shewed that helices tend to cause the 
needle to arrange itself in the direction of the axes of the he- 
lix ; but the right vertical helix caused the S. pole to dip ; the 
left vertical helix depressed the N. pole of the needle suspended 
in its axis. 18. All the phenomena tend to shew, that a ther- 
mo-electric apparatus becomes a real magnet ; and this idea is 
confirmed by Professor Cumming’s little apparatus, which is 
attracted and repelled by opposite poles of a magnet. 19. The 
disturbance of the equilibrium of temperature in thermo-mag- 
netic combinations is the cause of their influence ; for a piece of 
ice applied to either end of the rectangle produces effects just 
the reverse of those which follow the application of the spirit- 
lamp to that extremity. 19. The application of ice, or of the 
lamp, to the centre of the antimony, produced opposite devia- 
tions in two needles placed between the centre and extremities 
of the bar. 
Dr Traill thinks, that the phenomena of thermo-magnetic 
combinations favour Ampere's idea of magnetism being produ- 
ced by currents moving in opposite directions ; and lie shewed 
how these might be represented, by lapping a fine wire, as a left 
helix, round the sides of an antimonial thermo-magnetic combi- 
nation, and as a right helix around one composed of bismuth 
and copper, commencing the operation at the end supposed to 
be heated. 
The second part of the paper was on the application of ther- 
mo-magnetism to some of the phenomena of terrestrial magne- 
tism. The author conceives, that the disturbance of the equi- 
librium of the temperature of our planet, by the continual ac» 
