C. GENERAL PHYSICS. 165 



nation needles that are now made in England, and he rec- 

 ommends earnestly the incliuatorium as a portable magnetic 

 instrument, upon the score of accuracy, convenience, and 

 cheapness ; since with it one may make a complete series 

 of magnetic observations, without also carrying declinome- 

 ter, magnetometer, reflecting circle, theodolite, or clock. A 

 simple addition to the instrument even allows him to make 

 absolute as well as relative determinations. Poggenclorff 

 An?iale?i, CLIL, 619. 



NEW METHOD OF INVESTIGATING TERRESTRIAL MAGNETISM. 



In an inaugural dissertation ofDr.Haanel, of Albion, Mich- 

 igan, recently printed at Breslau, Germany, the advantages 

 of the galvano-metric method for the determination of the 

 earth's magnetism and its oscillations are elucidated; he 

 concludes that the method is well adapted to such determina- 

 tions, and that it will recommend itself by the following ad- 

 vantages: The instrumental constants need be determined 

 only once for all subsequent observations ; the oscillations 

 of the declination may be eliminated by properly arranging 

 the observations; Gauss's method of counting the vibrations 

 is dispensed with ; the magnetic power of the coil can be 

 increased or diminished at pleasure ; and the oscillations of 

 the coil are under perfect control of the observer. HaaneVs 

 Inaugural Dissertation, Breslau, 1873, 128. 



THE EFFECT OF MAGNETISM ON THE ELECTRIC DISCHARGE. 



The last work published by A. De la Rive relates to this 

 subject, in the early development of which he took so active 

 a part, namely, the effect of magnetism on the electric dis- 

 charge when the latter takes place through a rarefied gas. 

 In an earlier memoir on this subject he studied the case of 

 the magnet acting upon a discharge, the latter being perpen- 

 dicular to the magnet. He showed that in this case the 

 magnetism produced not only a deviation of the luminous 

 jet, but its condensation, its more intense brilliancy, and a 

 notable diminution of the elastic force of the gas in the por- 

 tion of the discharge which is more directly submitted to 

 the magnetic action. This augmentation of intensity varies 

 with the nature of the gas. It is least with hydrogen and 

 greatest with air; that is to say, the effect is more marked 



