1854. ] OF THE ROYAL INSTITUTION. 459 
Where the atoms, being fewer in a given space, are farther 
apart, or where, being good conductors, the current runs as freely 
over the surface as through the axis, then they do not form 
like groups to the molecules of magnetic matter, but are still con- 
sidered subject to a species of induction by the action of external 
magnets and currents ; and so give rise to Weber’s reverse currents. 
The induction of momentary currents and the rotation of a ray 
are considered by De la Rive as in conformity with such a sup- 
position of the electric state of the atoms and particles of matter. 
The Lecturer seemed to think that the great variety of 
these hypotheses and their rapid succession was rather a proof 
of weakness in this department of physical knowledge than of 
strength, and that the large assumptions which were made in 
turn for each should ever be present to the mind. Even in the 
most perfect of them, 7. e. De la Rive’s, these assumptions are 
very considerable; for it is necessary to conceive of the molecules 
as being flat or disc-like bodies, however numerous the atoms 
of each may be; also that the atoms of one molecule do not 
interfere with or break up the disposition of those of another 
molecule; also that electro-chemical action may consist with 
such a constituted molecule; also that the motive force of each 
atom current is resident in the axis, and on the other hand that 
the passage of the current over the surface offers resistance ; 
for unless there were a difference between the axial and the 
surface force in one direction or the other, the atoms would have 
no tendency to congregate in molecules. In making these 
remarks, however, the speaker had no thought of depreciating 
hypothesis or objecting to its right use. No discoverer could 
advance without it; and such exertions as those made by De la 
Rive, to bring into harmony thoughts which in their earlier forms 
were adverse to each other, were of the more value, because 
they were the exertions of a man who knew the value both of 
hypothesis and of laws, of theory and of fact, and had given 
proofs of the power of each by the productions of his own mind. 
Still the speaker advocated that mental reservation which kept 
hypothesis in its right place and which was ready to abandon it 
when it failed; and as examples referred to Newton, who (as is 
shewn by his Letters to Bentley) had very strong convictions of 
the physical nature of the lines of gravitating force, yet in what he 
publicly advanced stopped short at the law of action of the force, 
and thence deduced his great results ;— and also to Arago, who, 
discovering the phenomena of magnetic rotation, yet not per- 
ceiving their physical cause, had that philosophic power of mind 
which enabled him to refrain from suggesting one, 
(M. F.] 
