FEBRUARY 29, 1884.] 
1882, discussed the following questions: 1°. A rede- 
termination of the ohm. 2°. (a) Atmospheric electri- 
city; (0) protection against damage from telegraphic, 
telephonic, and electric-light wires ; (c) terrestrial 
currents on telegraphic wires; (d) establishment of 
an international telemeteorographic line. 3°. Deter- 
mination of a standard of light. 
After a prolonged discussion, it was concluded that 
further experiments upon the unit of electrical resist- 
ance were necessary before a standard ohm could be 
adopted; and the governments participating in the 
congress were invited to encourage independent de- 
terminations of this unit. The section on earth- 
currents and lightning-conductors recommended also 
that the various governments should favor systematic 
observations, and that independent lines should be 
provided for the study of earth-currents; that long 
subterranean telegraphic lines should be used also for 
this purpose. The section on the standard of light 
were in favor of employing asa standard the light 
emitted by a square centimetre of melting platinum. 
The congress was adjourned to October, 1883 ; and 
afterwards the French government notified the vari- 
ous governments participating in the congress, that 
April, 1884, would be a more agreeable time to the ma- 
jority of the congress than October. It is probable, 
therefore, that the congress will re-assemble during 
the coming spring. 
Since the last meeting of the congress, various new 
determinations of the ohm have been made. E. Dorn, 
by a modification of Weber’s second method, used also 
by Kohlrausch, has obtained the following value: — 
_,mm 
18. E. = 0.9482 x 10% Bee’ 
where S. E. denotes the Siemens or mercury unit. 
Lord Rayleigh has obtained .986 as the mean of 
the results of three independent determinations of the 
British association unit. Professor Rowland is at 
present engaged upon a careful redetermination of 
the ohm, using his apparatus for determining the 
mechanical equivalent of heat as a check upon the 
electromagnetic methods. 
The subject of the cause of electromotive force 
obtains and deserves attention. Exner has main- 
tained that there is no known case of chemical action 
without the development of electricity, and also of 
the development of electricity without chemical ac- 
tion. Braun controverts this conclusion. Exner finds 
that in a cell with zinc and platinum electrodes, and 
iodine or bromine as the liquid, a difference of elec- 
trical potential is obtained, notwithstanding the fact 
that iodine and bromine are elements, and cannot, 
therefore, be electrolytes. Exner believes the cause 
of this current is to be sought in chemical change. 
Braun shows that Exner did not take sufficient 
precautions to insure the purity of the iodine and 
bromine, and also to prevent the disturbing influ- 
ence of the aqueous vapor in the air. He shows 
that there are numerous cases in which we havea . 
development of electricity without chemical action, 
and also strong chemical action without the develop- 
ment of electricity. It is beginning to be perceived 
SCIENCE. 
259 
that the subject of thermal chemistry requires also a 
consideration of electromotive force. 
In a voluminous paper containing a large series of 
observations, Quincke endeavors to verify Maxwell’s 
conclusion that the square root of the dielectric con- 
stant must be equal to the index of refraction for 
light of the same substance. The several methods 
adopted give results which are not in accordance with 
Maxwell’s theory of light. Quincke explains the dif- 
ferent results obtained by different observers, as fol- 
lows: 1°. Experiments show a fluctuation in the 
values of the index of refraction which is due to the 
electric force; 2°. A comparatively long duration of 
the electric pressure causes a fall in the value of the 
index of refraction equivalent to the effect of a rise 
of temperature between 0.0001° and 0.1° C. (this in- 
creases with the difference in potential between the 
electrodes, and can be attributed to internal friction 
caused by electric attractions and repulsions between 
the particles of the fluid); 8°. The phenomena of the 
change of the index of refraction show that the elec- 
tric pressure has no analogy with hydrostatic press- 
ure; 4°. These changes in the index indicate changes 
in hydrostatic pressure in the interior of the fluid, 
which are caused by the electrical pressure, the fluid 
being set into vertical movements thereby; 5°. The 
electrical effects appear to be transmitted through 
the fluid by impulses, and not in a continuous man- 
ner. 
Julius Elster and Hans Geilel show that Zamboni’s 
dry piles can be used as accumulators. The copper 
pole of the pile is connected with the positive, and 
the tin pole with the negative, pole of a Holtz ma- 
chine. After the latter has been worked for a few 
minutes, the dry pile is found to be charged. After 
repeated discharges, the pile is found to contain a 
charge of considerable intensity. The authors recom- 
mend the following form of pile. The plates of the 
pile are strung, by means of a needle, upon a silk 
thread, and then stretched between the poles of a 
Holtz machine. A pile of eleven thousand pairs of 
plates, of one square centimetre surface, after ten 
minutes’ charging, gave sparks one millimetre long, 
and made a Geissler tube luminous. The light of the 
tube was continuous at first, and afterwards intermit- 
tent. ‘These piles are well suited to exhibit to a large 
audience the principle of Planté’s or Faure’s accumu- 
lators. 
An interesting report upon the transmission of 
power by electricity was presented by Cornu to the 
French academy in April, 1883. This report was 
that of a commission appointed to examine the ex- 
periments of Depretz. It was found that the work 
absorbed by the generatrix, and transmitted to the 
receptrix, increases with the velocity of the genera- 
trix. Depretz has succeeded in transmitting nearly 
four and a half horse-power through a resistance of 
a hundred and sixty ohms, which represents a double 
telegraph-line of eight and five-tenths kilometres.. 
The work received was thirty-seven and a half per 
cent of that spent. With a greater velocity of the 
generatrix, it seems possible to transmit power to 
greater distances than Depretz has attained. This 
