PHYSICS. 



By GEORaE F. Bakker, 



Professor of Physics in the University of Pennsylvania, Philadelphia. 



GENERAL,. 



The year 1882 has witnessed a marked physical progress, which is 

 nowhere so surprising as in the department of electricity. Of the four 

 hundred and thirty titles noted for the preparation of these abstracts, 

 two hundred and four, or nearly one-half, are uj)on subjects connected 

 with electricity and magnetism. 



In his inaugural address as professor of applied mathematics in 

 Owens College, Manchester, Dr. Schuster considers the influence of 

 mathematics on the progress of physics, tracing it from the time of 

 Galileo, the founder of mathematical physics, on the one side, and of 

 Baptista Porta and natural magic on the other, to the union of the two 

 in the science of to-day. He says: "The most important of all the 

 functions of mathematical physics, and perhaps the only one through 

 which mathematics has had an unmitigated beneficial influence on the 

 progress of physics, is derived from its power to work out to their last 

 consequences the assumptions and hypotheses of the experimentalist. 

 All our theories are necessarily incomplete, for they must be general 

 in order to avoid insurmountable difficulties. It is for the mathemati- 

 cian to find out how far experimental confirmation can be pushed, and 

 where a new hyi^othesis is necessary." {Nature, February, 1882, xxv,^ 

 p. 397.) 



Eoche, in a memoir upon the internal state of the terrestrial globe, 

 proposes the hypothesis that the earth is composed of a solid nucleus 

 covered with a less dense layer, partially liquid, perhaps, to a certain 

 depth. {Mem. Acad. Sci., 3fontpeUier, 1881 ; J. Phys., October, 1882, 11^ 

 I, p. 462.) 



Sir William Thomson has called attention to a thermodynamic accele- 

 ration of the earth's rotation, due to the action of the sun upoii the ter- 

 restrial atmosphere. He concludes that, in the course of a century, a 

 chronometer B (regulated to sidereal time day by day and year by year) 

 would be in advance of a chronometer A (regulated to sidereal time at 

 the commencement of the century, and keeping absolute time since) by 

 2.7 seconds in virtue of this thermodynamic acceleration, and behind it 

 by 25 seconds in consequence of the retardation due to the tides, the 



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