524 
Mr. Babbage on electrical 
doubt of the fact. I have occasionally shown it to several friends 
although I have not in every instance succeeded in this. 
To have omitted to state in this paper the fact of such a 
retrograde motion would have been un candid, because it si 
one which is strongly opposed to all the reasoning that it 
contains. To abstain from giving any explanation, however 
imperfect, that might reconcile it with my view of the sub- 
ject, would be to leave untouched a very powerful, and almost 
solitary argument against the explanation which I have pro- 
posed both of magnetic and electric rotation. I shall there- 
fore attempt to show, not merely that it is not repugnant to 
the principle which I have already explained, but that that 
very principle may, in certain circumstances, produce the 
retrograde motion, and that in others nearly similar, it shall 
not take place ; thus not merely showing the possibility of the 
fact, but accounting for its apparently capricious nature. 
In figure 2, N represents the end of an excited needle, 
situated above a metal plate C, and having a muslin screen 
G interposed between them. All three being at rest, the 
screen and the metal plate will become electric by induction, 
and one of the two following arrangements must take place : 
either the electricity developed on the screen and on the plate 
will be of the same species, in which case it will be contrary 
to that of the needle N ; or the electricity on the screen and 
the metal plate will be of different kinds, in which case one 
of them must be of the same species, the other of a different 
one from that of the needle. 
In the first case let B B represent the curve of the intensity 
of induced electricity on the muslin screen, that is, let each 
of its ordinates be supposed proportional to the electricity at 
