in a Letter to M. Gay-Lussac. 365 



• the revolution of the currents is circumscribed within narrow 

 limits, and there is little to add to the results that form the 

 basis of the [our] whole theory;" but that when the motion 

 is rapid the currents envelope the whole disc, (i so as to become 

 a species of labyrinth." For my part I believe the currents 

 have the same general direction as has been assigned to them 

 in the figures, whether the rotation be slow or rapid ; the only 

 difference is an increase of velocity. 



A circumstance is then selected which is really simple, though 

 it may at first appear complicated; namely, that in which the 

 opposite poles are adjusted over a disc in one diameter, but 

 towards the opposite edges on each side of the centre. This 

 circumstance, with the direction of the movement and the cur- 

 rent produced, is exhibited in fig. 7 of Messrs. Nobili and 

 Antenori's memoir. It is unnecessary to quote pages 296 and 

 297, which contain the explanation of this figure, but I shall 

 refer to fig. 12, which corresponds to it, and is in conformity 

 with my views and experiments, so that the two may be com- 

 pared together. It is very satisfactory to me to find, that in 

 this part of the memoir, as well as in the first, there is no im- 

 portant result of experiment contrary to my published opi- 

 nions, though I am very far from adopting the conclusions that 

 have been drawn from them. 



If figure 12 be examined, it will be instantly seen that it 

 results in the most simple manner from the action of the two 

 poles. Thus, as far as the upper or north pole only is con- 

 cerned, the currents are as in figure 6. But as with the north 

 pole, the current determined by it moves from the circumfe- 

 rence towards the centre, so with the south pole, in the same 

 or corresponding position, the currents move from the centre 

 to the circumference (F. 100.) ; and consequently in fig. 12 

 they are continued along the diameter N, S, through the centre 

 of the plate, to return in the direction of the arrows upon the 

 sides E, O. The points upon which I find my views to dis- 

 agree with the indications of the galvanometer obtained by 

 Messrs Nobili and Antenori are, first, the direction of the cur- 

 rents at N and S, which is contrary to what I obtained; and, 

 secondly, the existence of any oblique axis of power, as P, Q, 

 in their figure 7. 



The memoir concludes, at least as far as I am concerned, 

 at page 298, by again mentioning the error (but not as an 

 error) relative to the revolving disc, which becomes a ?icw 

 electrical machine. At the commencement, the authors being 

 little conversant with the principles under the influence of 

 which such a result is obtained, deny it; and though they 

 say here, " What shall we say after the nexv observations that 



