A New Form of Earth Inductor. 579 



produced in air as found by Bragg have been confirmed by a 

 more direct process. 



4. The energy of the alpha particle consumed in the pro- 

 duction of an ion depends upon the nature of the molecule 

 ionized. It apparently requires less energy to produce an 

 ion in the gases or vapours which have heavy or relatively 

 complex molecules than it does in those gases of lighter or 

 less complex molecules. 



Laboratory of Physic?, University of Illinois, 

 Urbana, Illinois, January 28, 1911. 



LXIY. A new Form of Earth Inductor. By James E. Ives, 

 Ph.D., Associate Professor of Physics, and 8. J. Mauchly, 

 of the University of Cincinnati*. 



THE instrument described in this paper is the result of a 

 desire of the authors to construct an Earth Inductor 

 which could be used to measure the vertical component of 

 the Earth's magnetic field directly, without the use of the 

 magnetometer and the ordinary rotating Earth Inductor. In 

 the form described, it was only used to measure the vertical 

 component, but it could easily be adapted to determine, 

 directly, all of the elements of the Earth's field. 



The essential parts of the device were a square of brass 

 tubing supported in a horizontal plane upon a wooden frame, 

 Ci^c 3 c 4 i n the perspective drawing of fig. 1 ; a sliding 

 conductor, s : s 2 , connecting two sides of the square, which 



could be moved parallel to itself ; and an insulated wire 

 enclosed within the tubing. In the figure, the brass tubing 

 is shown in solid, and the wooden frame in dotted lines. The 

 tubing had outer and inner diameters of 1*12 and *97 cm. 

 respectively. The square was 100 cms. long on a side, from 

 centre to centre of the tubing. It was cut in two places, 

 shown at a and b in fig. 1, on opposite sides. At a the gap 

 was 1*2 cm. long, and at b *3 cm. These gaps were filled in 

 * Communicated by the Authors?. 



