240 
Also, very often when adjusting the speed to obtain photographs for 
series B and E the discharge would change from one type to the other 
when the magnets were excited. Precht found that this was the ease, 
but these observations can hardly be compared with his, since point elec- 
trodes were used in this case, while he used one point and one blunt elec- 
trode. In all cases observed where a change occurred, if a brush dis- 
charge in a nonmagnetic field passed above or below a line directly be- 
tween the points as shown by the spark discharge EH, 1 and 4, and the mag- 
nets were excited to deflect the stream in such a way as to make the path 
of discharge shorter, it changed to a spark discharge. Or if a spark dis- 
charge passed directly between the points and was deflected it changed 
to a brush. In all cbserved cases (possibly 25 or 30) the transformation 
could be explained by the change of distance. 
The series G shows the effect of an air current on the path of dis- 
charge. The air current was led into the camera through the bottom side 
by means of a glass tube 2.25 em. in diameter so that the mouth of the 
elass tube was 2.2 cm. below the points, and flowed at the rate of about 
1,200 c © per second. Nos. 1 and 8 show the discharge without the air 
current, and Nos. 2 and 4 show deflection by the air current. It differs 
from the defiecticn produced by the magnetic field in that the greater de- 
flection here is with the negative stream. This indicates that the pressure 
is not as great in the negative stream as in the positive, which agrees with 
the work of 'S. Arrhenius, who measured the torsion produced by a sus- 
pended wire cross with points bent at right angles to point in the same 
direction and found that the tersion produced by the negatively charged 
wire was less than the positively charged wire, which was more clearly 
shown the lower the potential. (Note—It was intended to show a photo- 
graph with current in second direction, deflected by an air current. G 4, 
which should have shown this, shows a current in the same direction as 
G 2, which was due to a reversal of polarity of the machine. The error 
was not observed until the apparatus was tern down.) 
Series Hl shows photographs of the points when the poles of the ma- 
chine were placed close enough for a spark to pass between them.” It was 
found that when a spark passed between the poles of the machine there 
was a violet stream (brush) between the points. This violet stream did 
not usually pass directly from one point to the other, but was curved with 
1S. Arrhenius (.\nnal. Phys. Chem. 63, pp. 305-313), 1897. 
