336 Mr. 0. A. Chant on the Variation of 



The cylinders of {a) were 2*5 cms. in diameter and 12*5 cms. 

 long, with hemispherical ends ; the spheres of (b) were of 

 two sizes, namely, with diameters of 10 cms. and 30 cms. 

 respectively ; the larger spherical ends of (c) were 19 mm., 

 the smaller 6 mm., and the straight portion 4*2 mm. in 

 diameter, while the length over all was 12*5 cms. ; in (d) is 

 shown the ordinary Hertzian plate oscillator. 



The sparks were produced by an induction-coil capable of 

 giving sparks 12*5 cm. long, and fed by five accumulators in 

 series. 



The interrupter was similar to that used in the other in- 

 vestigation. It consisted in a platinum-tipped rod, which, 

 by means of a motor, was alternately plunged into and with- 

 drawn from mercury, the surface of which was kept clean by 

 a stream of water continually flowing over it. Tn series with 

 this were a pendulum interrupter and a contact-key. This 

 key was depressed during any desired number of 

 vibrations of the pendulum — usually five swings •=>' ' 



— during which time the coil was interrupted 

 approximately 60 times. This number, of course, 

 varied somewhat with the speed of the motor, 

 but it did not change much during any series 

 of readings. 



The magnetic detector was the same as that 

 used in the other research. It had twenty pieces 

 of iron, 0*014 cm. in diameter and 1 cm. long, 

 insulated from each other by paraffin, and wound 

 over with *,'0 turns of fine insulated wire. It 

 was mounted in the end of a glass tube, and all 

 held on a small sheet of hard rubber by means of 

 wax. It is shown one-half of natural size in 

 fig. 2. 



The magnetometer and telescope, as well as the 

 method of placing the detector behind the mag- 

 netometer, were as described in the former paper. 



The manner of producing the oscillations along the wires 

 is shown (for the cylinders) in fig. 3. AB is a long straight 



Fiff. 3. 



/I 



wire (0*7 mm. in diam.) ending at A in a small knob 6 mm. 

 in diameter, which was separated from an end of one of the 

 cylinders by a piece of mica, M, usually 0"15 mm. thick. 

 By this means the surgings on the cylinders were impressed 



