456 Intelligence and Miscellaneous Articles. 
had undergone great crumpling and folding after the process of folia- 
tion had been completed; hence that it was long anterior to the 
great earth-movements which had affected the Palaeozoic rocks of 
South Devon. He stated that the nature of those disturbances sug- 
gested that this district of South Devon had formed the flank of a 
mountain-range of some elevation, which had lain to the south. Of 
the foundations of this we may see traces in the crystalline gneisses 
of the Eddystone and of the Channel Islands, besides possibly the 
older rocks of South Cornwall and of Brittany. He also called 
attention to some very remarkable structures in the slaty series near 
Tor Cross, which appeared to him to throw light upon some of the 
structures observed at times in gneisses and other foliated rocks. 
2. " Notes on Brocchi's Collection of Subapennine Shells." By 
J. Gwyn Jeffreys, Esq., LL.D., E.R.S., E.G-.S. 
3. " British Cretaceous Nuculidse." By John Starkie Gardner, 
Esq., E.G.S. 
LXVII. Intelligence and Miscellaneous Articles. 
ON THE INDUCTION PRODUCED BY VARIATION OF THE INTENSITY 
OF THE ELECTRIC CURRENT IN A SPHERICAL SOLENOID. BY 
M. QUET. 
r PHE problem which I propose to solve is not without some 
-^ interest, for, supposing the solenoid of the same volume as the 
sun and at the same distance from the earth, it will be possible to 
examine whether (in spite of that enormous distance, and without 
the necessity of attributing to its electric currents momentary 
variations of intensity which would be excessive in comparison with 
those of our voltaic currents) its induction is capable of producing 
appreciable effects. It wi]l be seen further on what equivalence 
there exists between the real sun and the fictitious solenoidal sun 
in the point of view of terrestrial induction. 
Imagine upon the surface of a sphere a series of circular coils, 
parallel with each other, following at a constant distance, and tra- 
versed by the same electric current, the intensity of which under- 
goes at every point the same momentary variation. Barlow con- 
structed a solenoid of this description, the several circuits of which 
were excited by a single and constant current. The direction of 
the radius of the sphere which is perpendicular to the planes of the 
circles, and from which the currents are seen to move from right to 
left, is the axis of the solenoid. Erorn the point 0, the centre of 
the induced elementary mass m, I draw Ox perpendicular to the 
axis of the system, Oz parallel to this line, and Oy perpendicular 
to the plane zOx, to the left of Oz as personified and looking 
towards Ox. The inductive action of each circular current, and 
consequently that of the solenoid, is a force applied to the mass w 
and in a direction either similar or the reverse to Oy, according 
as the momentary variation is positive or negative. When the 
