260 
some other part of the building. It required at least two hours to complete 
the four series. The current and potential were read just before the pho- 
tographie plate was exposed. 
ELECTROSTATIC AND MAGNETIC FIELDS. 
The magnet was again placed in the position so that the line of dis- 
charge between the points was transverse to the magnetic lines of force, 
and with the electrostatic plates above and below the points, an attempt 
was made to balance the effect of the electrostatic field against that of the 
magnetie field. In this work the plates were charged by a Holtz machine 
with plates 43 cm. in diameter. A ground glass placed in the end of the 
camera opposite the pinhole showed clearly the path of discharge. The 
speed of the Holtz machine and the strength of the exciting current of 
the magnet were then regulated until the stream under the action of both 
fields was the same as when no field influenced it; then, the ground glass 
was removed and was replaced by a photographie plate. Two series of 
these photographs are shown here, M, for the spark discharge which, under 
the influence of magnetism alone was changed to brush, and N for the rich 
spark. It was not difficult to balance the two fields in the case of the 
rich spark, but with the unstable spark they were not successfully balanced. 
Sometimes with this type a very low magnetic field seemed to predominate 
over the electric field. This, if true, conforms with the statement made 
in the previous report that the mugnetic effect is greatest when the dis- 
charge is on the verge of changing from one form to the other. Data as 
follows: 
Distance between points, 18.05 em. ITI is the magnetic field strength in 
gausses. 
TABLE 4. 
Nintiéamee | 1. a kee Man dee Beek ide 
, anti ~otenti : ; 4 alues for 
between Potential | Po ential | Velocity of Form of ? 
Plates | Difference | Gradient | H I Disch: ly 
: seerraitas heise al on ischarge | 
in cm. in Vorts 4 m | 
1 5.4 14600 | 2710 | 4300 | 6.3x107 | small brush | 7.8 x10? 
2 5.4 14600 | 2710 4300 6.3x 10" occasional spark 7.5 x 10? 
3 5.4 15000 | 2780 2550 1.9x 10° wo eet) xal0e 
4 5.4 15000 2780 «| 3800 | 7.4x 10! rich spark 1,92 108 
5 6.1 26890 | 4360 | 1600 2.7x 10° spark 1.36x 10° | Series M 
6 6.1 26800 | 4360 | 1600 2.7x 10° rich spark 1.36x 10° | Seriee N 
| 
