830 
its adult form and may be termed Leptocephalus 
diptychus. 
C. H. EIGENMANN, 
CLARENCE KENNEDY. 
UNIVERSITY OF INDIANA. 
VELOCITY OF IONS FROM ELECTRIC ARCS AND 
FROM HOT WIRES. 
Mucu interest is being shown at present con- 
cerning ionization of gases and ‘electron’ the- 
ories of electricity. An investigation now in 
progress promises to throw further light on 
this subject, in fact to change one idea which 
has been held. It has been stated by eminent 
authorities that in the case of discharge through 
gases the negative ions always go faster than 
the positive under the same conditions. The 
present investigation shows that this is not 
always the case and a brief account of it may 
not be amiss. 
The work had its origin in an attempt to ex- 
plain the phenomena of the electric are. It 
was shown in the Physical Review * that all the 
phenomena of the are could be explained by 
assuming, first, that the current in the are was 
carried by ions, and second, that the positive 
ions move the more rapidly. The second part 
of this hypothesis did not at first seem probable, 
since in all cases which had previously been in- 
vestigated the negative ions had been found to 
move the more rapidly. Two sets of experi- 
ments were, however, given as tending to sub- 
stantiate that hypothesis, but neither of them 
could be considered conclusive. + 
More recently experiments have been per- 
formed with ions drawn out from an are by a 
charged body in the neighborhood.{ The posi- 
tive ions in this case were found to have the 
greater velocity. Quite recently the same 
fact has been shown by an application of a 
* Phys. Rev., 10, 151. 
{Since publishing the above-mentioned article I 
find that part of the work there described had already 
been described by Dewar (Chem. News, 45, 37). My 
own work was performed without knowledge of that 
done by Dewar, and the method used was not the 
same as his. The results of the two investigations 
agree fully. The explanation of the results offered 
by myself was not suggested in his article. 
{ Phys. Rev., 12, 137. 
SCIENCE. 
[N.S. Vou. XIII. No. 334. 
method used by Zeleny * for finding the velocity 
of ions produced by X-rays. These methods 
are entirely independent and the agreement of 
the results in the two cases leaves little reason 
to doubt the correctness of the conclusion that 
the positive ions here move the more rapidly. 
Of course, this is not a proof that the posi- 
tive ions in the arc itself move more rapidly 
than the negative, but since such an assump- 
tion would explain the phenomena of the are 
and since the positive ions just outside the are 
do have the greater velocity, it seems reason- 
able to assume that they do also within the arc. 
It opens up, however, a still more interesting 
field of inquiry, 7. e., that concerning the con- 
dition under which the positive ions show this 
peculiarity. The discharge from hot platinum 
and iron wires was accordingly investigated. It 
has long been known that positive electricity 
escapes from hot metals easier than negative. 
An examination of the velocity of the ions 
from the hot metals showed that here also 
the positive ions move the more rapidly. Both 
the methods used in the previous investiga- 
tion led to the same conclusion. 
But in all these cases the action is compli- 
cated by the fact that both gases and solids are 
present. For example, in the case of dis- 
. charge from hot platinum wire atoms of plati- 
num are no doubt given off, since it is a well- 
known fact that platinum wire when heated to 
a white heat decreases in weight. + It may be 
that because of some contact difference of po- 
tential the negative ions of the metal never 
escape from the metal. A comparison of posi- 
tive ions of one substance with negative of an- 
other would not be of great value. One would 
wish to know whether the positive ions move 
faster than the negative ions from which they 
have been separated. 
The case of the arc is still more complicated, 
for many different solid and gaseous substances 
enter into the are. The investigation by 
Arons { on the are between metals in H and N 
at different pressures shows that both the ter- 
minals of the are and the gases about it must. 
be considered. 
* Phil. Trans. Roy. Soc. Lon., 195, 193. 
+ Wied. Ann., 37, 319. 
{ Drude Ann., 1, 700. 
