200 FE. H. Hall on a New Action of the 
the writer long since suggested, by the existence on the west, 
near by, of the stable Archean area of the Adirondacks. 
In conciusion, I repeat the considerations that have been 
presented : 
1. The western half of the region between the Connecticut 
River valley and the Hudson River, that is, the western half 
of the Green Mountain area, is proved to consist of rocks that 
are (1) of Lower Silurian age; and (2) of one orological system. 
2. The schistose rocks of the eastern half in Vermont are 
to a large extent similar to those of the western. 
8. The rocks of the central mountain section in Ver- 
mont are, in its northern part, identical schists (hydromica, etc.), 
with those on the east and west sides of it. 
of great magnitude. 
In view of these various considerations, the evidence, al- 
though not yet beyond question, is manifestly strong for em- 
bracing the whole region between the Connecticut and the 
Hudson (and to an unascertained distance beyond) within the 
limits of the Green Mountain synclinorium. 
Art. XX V.—Ona New Action of the Magnet on Electric Currents;* 
by E. H. Hatt, Fellow of the Johns Hopkins University. 
SomETIME during the last University year, while I was read- 
ing Maxwell's Electricity and Magnetism in connection with 
Professor Rowland’s lectures, my attention was particularly at 
tracted by the following passage in vol. ii, p. 144: 
“Tt must be carefully remembered, that the mechanical foree 
which urges a conductor carrying a current across the lines of 
magnetic force, acts, not on the electric current, but on the con 
ductor which carries it. If the conductor be a rotating disk or 
* From the American Journal of Mathematics, vol. ii., 1879. 
