198 
four kilograms. The screw consists of two helicoidal 
pallets covered with varnished silk, the deformation 
of which is guarded against by the action of coils of 
steel wire. This screw is 2.85 metres in diameter: 
it is attached to the machine by a transfer and by 
gearing, and makes a hundred and eighty revolutions 
per minute, while the bobbin makes eighteen hun- 
dred. 
The electric battery, which may be called the gen- 
erator of the screw balloon, has the same surface of 
zine and carbon as our trial batteries, the measure- 
ment of which has already been given elsewhere (La 
Nature, May 20, 1882), the same number of cells, 
the same volume of liquid. We are able to consider- 
ably reduce its capacity by using four ebonite troughs 
with six compartments, instead of twenty-four sepa- 
rate receivers. Besides, we use slightly higher vessels, 
which also gives greater breadth. Fig. 3 presents 
one of the four batteries used in the electric balloon 
as it was tried in the laboratory. It consists, as may 
be seen, of one large trough with six divisions; each 
compartment forming an element of the pile, enclosed 
and mounted on copper legs, having eleven thin car- - 
bons and ten zincs arranged alternately. The zines 
are held in place from above by flexible 
pincers, and may easily be renewed after 
each experiment: they are .15 of a 
centimetre thick, sufficient to 
work the battery for three 
hours. They must be perfect- 
ly amalgamated. Each com- 
partment is provided at its low- 
er part with a slender ebonite 
tube, which communicates to a 
lateral conduit connected by a 
caoutchouc tube with a large 
and very light ebonite vessel 
containing the acid solution of 
bichromate of potassium. If 
the pail is raised by means of a 
string passing into the blocks above the level of the 
battery, the latter is filled by the chief communicating 
vessel, the liquid acts on the zines, and the current 
passes: if the pail is lowered, so that it occupies the 
position seen in fig. 3, the liquid enters by the caout- 
chouc tube, the battery becomes empty, and ceases to 
act. By this system it is apparent that the piles com- 
municate with each other solely by the narrow con- 
duits. The resistance of the liquid is great enough 
for this communication to have no effect on the cur- 
rent, although the elements are in series. In the car 
there are four batteries like that shown in the figure, of 
twenty-four elements, in series, and fed by four pails 
of ebonite, each containing thirty litres of the bichro- 
mate of potassium solution. The batteries are stowed 
away in the car (which is 1.9 metres long and 1.45 
metres broad) so as to occupy the least possible room. 
Two ebonite troughs of twelve elements are placed 
cross-wise about .35 of a metre from the bottom of the 
ear, and there are two more .15 of a metre higher. 
The ebonite reservoirs at the two back corners of the 
car feed the upper piles; and the other two reservoirs, 
nearer the battery, feed the lower piles (fig 4). A 
od 5 
we 
SCIENCE. 
ie. 1. —Skull of Diplodocus longus Marsh, side view. 
vacant space is left between the four pails for the 
operator, who controls every thing, having at hand 
the cords to-raise the pails, the hooks to hold the 
cords at the desired height, the commutator with 
the cup of mercury to start the current, and the cords 
the rudder. 
The bichromate of potassium used to work the bat- 
tery is concentrated and very acid: it is turned into 
the pails at a temperature of about 40°, which per- 
mits of a considerable increase in the quantity of 
dissolved salt. The commutator is so arranged that 
a current of six, twelve, eighteen, or twenty-four ele- 
ments may pass; and thus the screw has four veloci- 
ties. The four pails are covered with a sheet of caout- 
chouc, pierced with one small hole, which allows the © 
air to pass when the liquid is flowing, and is bound 
around the pail by a copper thread sheathed in gutta- 
percha. This manner of closing is very secure; and, in 
case of a shock, not a drop of the liquid can escape. 
The pails, when empty, weigh only three kilograms 
each: they are strengthened by basket-work, which 
also serves as a support. Cords passing into the pul- 
leys raise them above the piles in order to fill them, 
and lower them to empty them. The bottom of the 
car holds a caoutchoue cistern to receive the liquid 
in case of accident. The pile with the liquid weighs 
about a hundred and eighty kilograms. A little 
willow basket —easily seen in our illustration —is 
placed under the motor. It contains an oil-can for 
the motor, a little bottle of mercury to supply the 
cups of the commutator sunk into a block of box- 
wood, and also the tools necessary to discharge the 
pile in case of accident. All this occupies the back 
of the car. In the front, space is reserved for the 
ballast-bags and for the implements used in the 
descent. 
Our. illustration was made with great exactness: it 
presents all the details of the arrangement of the 
car, and shows the attachment of the motor. The 
