4-80 Scientific Intelligence. 



cury cups, in the ordinary form of lecture apparatus for showing 

 Ampere's laws, Raps has devised a system of two rolling metal- 

 lic contacts, by means of which the electric current can be led to 

 and away from the model. To show the applicability of the 

 apparatus he instances this case. A solenoid of 15 cm diameter, 

 40 cm in length, with 70 turns of aluminum wire, Avith a current of 

 6 amperes, places itself in the magnetic meridian. — Physical 

 Society of Berlin, Oct. 20, 1893. Ann, der Physik und Chemie, 

 No. 4,' 1894, p. 29. j. t. 



12. Magnetisation of Iron by rapid Electrical Oscillations. — 

 Klemencic, at a recent meeting of the Kaiserliche Akademie der 

 Wissenschaft ol Vienna, read a paper on this subject. The value 

 of /a, the magnetic permeability was determined by a heat 

 method. The following are some of the values obtained for /i : 

 Soft iron 118, soft steel wire 106, hard steel wire 115, soft 

 Bessemer steel 77, hard 74, nickel 27. These values agree fairly 

 well with those of Rayleigh and Bauer for very feeble magnetis- 

 ing forces. It appears that Bauer and Rayleigh's results for 

 longitudinal magnetism also apply to circular magnetism. — 

 Nature, April 26, 1894, p. 607. ' j. t. 



II. Geology and Minekalog-y. 



1. On the Straining of the Earth resulting from Secular Cool- 

 ing ; by Chables Davison. Read before the Royal Society, 

 London, January 10, 1894. (Abstract.) — If the coefficient of 

 dilatation (e) and the conductivity (k) are constant for every 

 point within the earth, and if the temperature (V) was initially 

 the same throughout, the depth of the surface of zero-strain after 

 100 million years is 2*17 miles, the total volume of the crust 

 folded and crushed above that surface is about 184,500 cubic 

 miles, and the mean thickness of the crushed rock spread over the 

 whole surface of the earth is 4*95 ft. (taking e=0"0000057), k= 

 400, V"=7000° F.). The smallness of these figures has been 

 claimed by some geologists as a new and strong argument against 

 the contraction theory of mountain evolution. 



In the present paper the problem is reconsidered on the suppo- 

 sition that the coefficient of dilatation is not constant, but in- 

 creases with the temperature, the change in the former varying 

 as the corresponding change in the latter. It follows, from ex- 

 periments made by Fizeau, that, for a rise of one degree in tem- 

 perature, the coefficient of dilatation increases on an average by 

 about 1/888. Adopting this value, and taking the other constants 

 as above, it is found that, after 100 million years, the depth of 

 the surface of zero strain is 7*79 miles, the total volume of crust- 

 folding about 6,145,000 cubic miles, and the mean thickness of 

 the layer formed by spreading it over the whole earth 164*7 ft. 



If the conductivity increases with the temperature, or if the 

 material which composes the earth's interior be such that the con- 

 ductivity and coefficient of dilatation are greater in it than in the 



