494 Mr. Bowlker on the Lengthening of the Spark from 
Compare these results with those from a bare assister 
separated from the anode by a vulcanite screen. 
y 
Spark-gap. 
PMNGSsISted).. Uhisgoe eo. pss... ocak Ree 45 mm. 
Assisteridustant: Gear) ss. sc. «2 RE 63 
Assister distant.12 (detached) ............ 79 
Assister distant 12 (attached) ............ 72 
Experiments were tried to find the effect of a metal screen 
in addition to the vuleanite screen. 
A tin plate about 30 em. square was placed touching the 
vulcanite screen and on the same side of it as the assister ; 
the assister used was 160 mm. long, with 100 mm. of its 
length in a glass bottle. | 
Assister distance XA=85 mm. The results were :— 
Spark-gap. 
Tin insulated. Tin a 
ee ae re 48 iy | i. 77 
| Assister attached ...... 78 mm. 78 mm. 
| Assister detached...... 87 mm. 97 mm. 
Next a plate of lead, 200 mm.x 140 mm. x 1:5 mm. was 
used—in some of the experiments the lead was put to earth. 
Results:— 
Spark-gap. 
Without lead. | Lead insulated., Lead to earth. 
Unassisted..... Poetaes ol 3 82 mm. . 82 mm. | 95 mm. 
Assister attached ...... 87 mm. | 82 mm. 95 mm, 
Assister detached...... 109 mm. | 97 mm. 98 mm. 
When the lead is insulated it stops the whole of the effect 
of the attached assister, and when put to earth almost the 
whole of the effect of the detached assister. (Note the 
increased length of spark due to the presence of the earthed 
lead plate—its distance from the anode was 48 mm.) 
The effect of altering the length of the assisters was tried. 
Assisters of wire 1°6 mm. in diameter. 
