t>70 Mr. Sturgeon on a rotative thenno-magnetical Experiment- 



the top of the magnet, and along that part of the magnet 

 from the top to the quicksilver in the cell F E : and lastly, 

 along the silver wire from the point 5 to the extremity at P, 

 where it joins the platinum. 



The other part of the wire machine being on the same 

 principle as that described, the platinum arms of this apparatus, 

 when heated by a spirit lamp or otherwise at the extremities 

 PP, are in every respect assimilated to the arms of the rotating 

 cylinder of Ampere; for the electric fluid is transmitted in 

 the same direction through both arms of the apparatus ; and 

 hence the rotating tendency is constant round a central mag- 

 net ; and not impulsive, as in other rotations with an external 

 magnet. 



The moveable part of this machine (which is the platinum 

 and silver wires only) will rotate with a facility proportioned 

 to the delicacy of the suspension, the difference of tempera- 

 ture of the parts P and c of each arm, the power of the mag- 

 net, and the dexterity of the experiments. And I must here 

 warn the reader, that this last requisite is not the least to en- 

 sure success in the experiment ; lor had I not been satisfied 

 that the apparatus was constructed upon principle, I probably 

 might not have persevered sufficiently to attain my object. 

 However, a slight modification of the apparatus considerably 

 facilitates the experiment, and renders it more permanent 

 and beautiful. 



A circle of lamps are placed on a stage of the same figure, 

 in such a manner that they may coincide with the periphery 

 of the circle described by the points P P of the wire part of 

 the machine, so that the latter may constantly be kept at 

 nearly the same temperature in every part of their revolution. 

 And the shoulder of those arms, or that part of the platinum 

 wire to which the pivot c is soldered, is kept at as low a tem- 

 perature as possible by means of ether or other cooling liquid. 



If instead of lamps a^circular flame of ignited hydrogen be 

 substituted, and regulated by a stop-cock, this part of the 

 apparatus may perhaps be considered at its acme of per- 

 fection. 



Another improvement is by having a conducting wire from 

 the pivot c to the metallic cell F E, in the same manner as 

 the conducting wire of the copper part of M. Ampere's ro- 

 tating cylinders; through the upper part of this conducting 

 wire passes a screw with a milled head, made into the form of 

 a cup. The pivot c runs in this cup, at the bottom of which 

 is a small globule of mercury, for the better ensuring the con- 

 tact. The cup is then filled up with ether, and may be sup- 

 plied during the experiment in proportion to the evaporation. 



The 



