The following are the principal numerical data of the new zinc accumulator.

PHYSICAL DATA.

E. Electromotive force. 2.36 volts.  R. Mean resistance. 0.02 ohm.  I. Normal intensity of the discharge current. 25 amperes. i.  Intensity of the charge current. 5 to 10 amperes.  Q. Capacity of accumulation after 200 hours’ formation. 550,000 couples.

DATA CONCERNING CONSTRUCTION.

Efficient surface of the 4 positive electrodes. 200 square dec. 
Efficient surface of the 3 negative electrodes. 15 square dec. 
Weight of the positive electrodes. 8.2 kilogrammes. 
Weight of the negative electrodes. 1.4 kilogrammes. 
Weight of the trough. 2.7 kilogrammes. 
Weight of the liquid. 4.4 kilogrammes. 
Weight of the attachments. 0.46 kilogrammes. 
Weight, total. 17.16 kilogrammes.

The total electric work stored up is 130,000 kilogrammeters, or 7,600 kilogrammeters per kilogramme of accumulator.  Theory indicates that a zinc accumulator might store up as much as 15,600 kilogrammeters per kilogramme.  If the present model gives half less, it is because I have purposely exaggerated the solidity of the trough and the mass of the electrodes.

It should be remarked that this capacity of 7,600 kilogrammeters per kilogramme is much greater than that of any other accumulator constructed in France.  The new model possesses, then, despite the size of the positives and the box, a relative lightness that will permit it to take a place upon electric locomotives as well as in fixed installations.

Independently of their use as accumulators, secondary zinc batteries may be utilized as regulating voltameters in lighting by incandescence, for deadening piston strokes, attenuating the irregularities in speed, and covering accidental stoppages.—­E.  Reynier, in La Nature.

* * * * *

THE HISTORY OF A LIGHTNING FLASH.

By W. SLINGO.

Lately we have all felt, I doubt not, a considerable amount of interest in the various phenomena attending this summer’s unusually heavy thunderstorms, accompanied, as they have been, by vivid lightning discharges of a more or less hurtful nature.  The list of disasters published in Knowledge, No. 143, might be very materially augmented were we to record such damage as has been wrought since that list was compiled.

There is not, I suppose, in the mind of any intelligent man at the present day a doubt as to the electrical origin of a lightning flash.  The questions to be considered are rather whence comes the electricity, and in what way is the thunderstorm brought about.  In attempting to answer these questions, sight must not be lost of the fact that the very nature of electricity is in itself almost sufficient to baffle any effort put forth to ascertain from lightning, as such, its whence and its whither.