88 Scientific Intelligence. 



revolve around a conductor carrying a current, and whether the 

 well-known pieces of apparatus in physical cabinets which are 

 supposed to illustrate the revolution represent a true phenomenon. 

 He arrives at the conclusion that Biot and Savart's law, which is 

 interpreted without reference to the position of the leading-in 

 wires, is incorrect, and that the observed rotations are entirely 

 due to the leading-in wires. It is impossible apparently to get 

 rid of the effect of these wires in any of the pieces of apparatus 

 which have been devised. There is however no theoretical 

 ground for the existence of the rotation, since action and reaction 

 are equal. H. Lorberg also discusses the point of contention be- 

 tween Lecher and Konig, and shows that in his Lehrbuch der 

 Physik he arrived at Lecher's conclusion. — Ann. der Physik, No. 

 11, 1900, pp. 513-529. J. T. 



8. Electron theory of metals. — The most important paper of 

 the last issue of the Annalen der Physik is that of P. Drude on 

 this subject. The author seeks to explain the electric current and 

 its effects in the magnetic field by the hypothesis of the move- 

 ment of electrons or corpuscles between the atoms of the metals 

 of the conductors. He finds a sufficient amount of agreement 

 with known facts to make the theory plausible, but he points out 

 that it is highly desirable to collect together observations on the 

 four transverse-galvanic and thermo-magnetic effects, together 

 with the thermic, the electric conductivity and the Thomson effect 

 in the same piece of metal, in order to prove his theory. — Ann. 

 der Physik, No. 11, 1900, pp. 369-402. , j. t. 



9. A simple modification of the Wehnelt interrupter, — This 

 consists in substituting a steel wire for the positive electrode 

 while the negative electrode consists of a copper wire. Both 

 wires are enclosed in glass tubes, except at the ends. — Ann. der 

 Physik, No 11, 1900, pp. 543-544. j. t. 



II. Geology and Mineralogy. 



v/ 1. Geological and Natural History Survey of Minnesota, 

 Vol. V. Structural and Petrographic Geology of the Taconic 

 and Archean ; by N. H. Winchell, assisted by U. S. Grant. 

 4°, pp. 1027, pi. 6, St. Paul, 1900. — It would be impossible in the 

 limits of a brief mention like this to do much more than merely 

 state that this volume contains an enormous mass of detailed 

 observations on and descriptions of the rocks of Minnesota. 



The first part, of some seventy-five pages, is by Prof. Winchell, 

 and gives a resume of his views on the general structure, age, 

 origin, relationships and petrology of the rocks of the State. 



The second part, by both authors, covers the detailed study 

 of some three thousand thin sections from every part of the 

 area. The occurrences are so numbered that the descriptions can 

 be referred to their appropriate places in the earlier reports of 

 the Survey. As is already well known, the great mass of this 

 work relates to rocks of the gabbroid family. 



