Nipher—On the Nature of the Electric Discharge. 5 
a substance having gaseous form. In a gas we may have 
freely moving positive ions as well as freely moving nega- 
tive ions. This is the condition in the Geissler and 
Crookes tubes. In a solid conductor we may also have a 
displacement of negative ions. The positive ions cannot 
move. They constitute the conductor. In such a con- 
ductor, so far as position is concerned, molecules are al- 
ways and constantly related to neighboring molecules as 
gaseous molecules are when they collide. The lower the 
temperature of the solid, the more nearly the molecules 
approach each other, and the more easily negative ions or 
particles are displaced from molecule to molecule. In 
other words, conduction is improved by a decrease of 
temperature. In the solid conductor, there is no evidence 
of the existence of a positive current. The positive ions 
which exist in the gases of the Crookes and Geissler tubes 
could not flow through a copper wire. 
There has been of late a tendency to return to the one- 
fluid theory. A few phenomena will be described which 
appear to favor Franklin’s view of the nature of elec- 
tricity. 
In 1900 in a paper in these transactions entitled, ‘‘On 
Certain Properties of Light-Struck Photographic 
Plates,’’* I have described a phenomenon which has some 
resemblance to what has been called ball lightning. Fig- 
ures 8, 9 and 10 of that paper show traces on a photo- 
graphic film, made by a slowly moving point of light. The 
motion of the point of light was always in the direction 
of flow of a negative discharge, and came from the nega- 
tive terminal of an influence machine. A metal disc hay- 
ing a diameter of a centimeter was armed with a pin- 
point. The point was bent over so that when the disc was 
placed on the film, the point made intimate contact with 
the film. The point rested upon a short pencil mark on 
the film. A slight moistening of the pencil mark is of ad- 
vantage. The knobs of the machine should be widely sep- 
arated, and it is of advantage to place a large sheet of 
8’ Trans. Vol. X, No. 6. 
