Scientific American Supplement No. 275

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In studying the stratifications observed in vacuum tubes, Dr. de la Rue
finds that they originate at the positive pole, and that their steadiness
may be regulated by the resistance in circuit, and that even when the least
tremor cannot be detected by the eye, they are still produced by rapid
pulsations which may be as frequent as ten millions per second.

Dr. de la Rue concluded his interesting discourse by exhibiting some of the
finest tubes of his numerous and unsurpassed collection.--_Engineering_

* * * * *

MEASURING ELECTROMOTIVE FORCE.

Coulomb's torsion balance has been adapted by M. Baille to the measurement
of low electromotive forces in a very successful manner, and has been found
preferable by him to the delicate electrometers of Sir W. Thomson. It
is necessary to guard it from disturbances due to extraneous electric
influences and the trembling of the ground. These can be eliminated
completely by encircling the instrument in a metal case connected to
earth, and mounting it on solid pillars in a still place. Heat also has a
disturbing effect, and makes itself felt in the torsion of the fiber and
the cage surrounding the lever. These effects are warded off by inclosing
the instrument in a non-conducting jacket of wood shavings.

The apparatus of M. Baille consists of an annealed silver torsion wire of
2.70 meters long, and a lever 0.50 meter long, carrying at each extremity
a ball of copper, gilded, and three centimeters in diameter. Similar balls
are fixed at the corners of a square 20.5 meters in the side, and connected
in diagonal pairs by fine wire. The lever placed at equal distances from
the fixed balls communicates, by the medium of the torsion wire, with the
positive pole of a battery, P, the other pole being to earth.

Owing to some unaccountable variations in the change of the lever or
needle, M. Baille was obliged to measure the change at each observation.
This was done by joining the + pole of the battery to the needle, and one
pair of the fixed balls, and observing the deflection; then the deflection
produced by the other balls was observed. This operation was repeated
several times.

The battery, X, to be measured consisted of ten similar elements, and one
pole of it was connected to the fixed balls, while the other pole was
connected to the earth. The needle, of course, remained in contact with the
+ pole of the charging battery, P.

The deflections were read from a clear glass scale, placed at a distance
of 3.30 meters from the needle, and the results worked out from Coulomb's
static formula,

C a = (4 m m')/d squared, with

______________
/ sum((p/g) r squared)
O = / -------------
\/ C

[TEX: O = \sqrt{\frac{\sum \frac{p}{g} r^2}{C}}]

In M. Baillie's experiments, O = 437 cubed, and sum(pr squared)= 32171.6 (centimeter
grammes), the needle having been constructed of a geometrical form.

The following numbers represent the potential of an element of the
battery--that is to say, the quantity of electricity that the pole of that
battery spreads upon a sphere of one centimeter radius. They are expressed
in units of electricity, the unit being the quantity of electricity which,
acting upon a similar unit at a distance of one centimeter, produces a
repulsion equal to one gramme:

Volta pile 0.03415 open circuit.
Zinc, sulphate of copper, copper 0.02997 "
Zinc, acidulated water, copper, sulphate of copper 0.03709 "
Zinc, salt water, carbon peroxide of manganese 0.05282 "
Zinc, salt water, platinum, chloride of platinum 0.05027 "
Zinc, acidulated water, carbon nitric acid 0.06285 "

These results were obtained just upon charging the batteries, and are,
therefore, slightly higher than the potentials given after the batteries
became older. The sulphate of copper cells kept about their maximum value
longest, but they showed variations of about 10 per cent.

* * * * *

TELEPHONY BY THERMIC CURRENTS.

While in telephonic arrangements, based upon the principle of magnetic
induction, a relatively considerable expenditure of force is required in
order to set the tightly stretched membrane in vibration, in the so-called
carbon telephones only a very feeble impulse is required to produce the
differences in the current necessary for the transmission of sounds. In
order to produce relatively strong currents, even in case of sound-action
of a minimum strength, Franz Kroettlinger, of Vienna, has made an
interesting experiment to use thermo electric currents for the transmission
of sound to a distance. The apparatus which he has constructed is
exceedingly simple. A current of hot air flowing from below upward is
deflected more or less from its direction by the human voice. By its action
an adjacent thermo-battery is excited, whose current passes through the
spiral of an ordinary telephone, which serves as the receiving instrument.
As a source of heat the inventor uses a common stearine candle, the flame
of which is kept at one and the same level by means of a spring similar to
those used in carriage lamps. On one side of the candle is a sheet metal
voice funnel fixed upon a support, its mouth being covered with a movable
sliding disk, fitted with a suitable number of small apertures. On the
other side a similar support holds a funnel-shaped thermo-battery. The
single bars of metal forming this battery are very thin, and of such a
shape that they may cool as quickly as possible. Both the speaking-funnel
and the battery can be made to approach, at will, to the stream of warm air
rising up from the flame. The entire apparatus is inclosed in a tin case
in such a manner that only the aperture of the voice-funnel and the polar
clamps for securing the conducting wires appear on the outside. The inside
of the case is suitably stayed to prevent vibration. On speaking into the
mouth-piece of the funnel, the sound-waves occasion undulations in the
column of hot air which are communicated to the thermo-battery, and in this
manner corresponding differences are produced in the currents in the wires
leading to the receiving instrument.--_Oesterreichische-Ungarische Post._

* * * * *

THE TELECTROSCOPE.

By MONS. SENLECQ, of Ardres.

This apparatus, which is intended to transmit to a distance through a
telegraphic wire pictures taken on the plate of a camera, was invented in
the early part of 1877 by M. Senlecq, of Ardres. A description of the first
specification submitted by M. Senlecq to M. du Moncel, member of the
Paris Academy of Sciences, appeared in all the continental and American
scientific journals. Since then the apparatus has everywhere occupied the
attention of prominent electricians, who have striven to improve on it.
Among these we may mention MM. Ayrton, Perry, Sawyer (of New York),
Sargent (of Philadelphia), Brown (of London), Carey (of Boston), Tighe (of
Pittsburg), and Graham Bell himself. Some experimenters have used many
wires, bound together cable-wise, others one wire only. The result has
been, on the one hand, confusion of conductors beyond a certain distance,
with the absolute impossibility of obtaining perfect insulation; and,
on the other hand, an utter want of synchronism. The unequal and slow
sensitiveness of the selenium likewise obstructed the proper working of the
apparatus. Now, without a relative simplicity in the arrangement of the
conducting wires intended to convey to a distance the electric current with
its variations of intensity, without a perfect and rapid synchronism
acting concurrently with the luminous impressions, so as to insure the
simultaneous action of transmitter and receiver, without, in fine, an
increased sensitiveness in the selenium, the idea of the telectroscope
could not be realized. M. Senlecq has fortunately surmounted most of these
main obstacles, and we give to-day a description of the latest apparatus he
has contrived.

TRANSMITTER.

A brass plate, A, whereon the rays of light impinge inside a camera, in
their various forms and colors, from the external objects placed before the
lens, the said plate being coated with selenium on the side intended to
face the dark portion of the camera This brass plate has its entire surface
perforated with small holes as near to one another as practicable. These
holes are filled with selenium, heated, and then cooled very slowly, so as
to obtain the maximum sensitiveness. A small brass wire passes through the
selenium in each hole, without, however, touching the plate, on to the
rectangular and vertical ebonite plate, B, Fig. 1, from under this plate
at point, C. Thus, every wire passing through plate, A, has its point
of contact above the plate, B, lengthwise. With this view the wires are
clustered together when leaving the camera, and thence stretch to their
corresponding points of contact on plate, B, along line, C C. The surface
of brass, A, is in permanent contact with the positive pole of the battery
(selenium). On each side of plate, B, are let in two brass rails, D and E,
whereon the slide hereinafter described works.

[Illustration: Fig. 1]

Rail, E, communicates with the line wire intended to conduct the various
light and shade vibrations. Rail, D, is connected with the battery wire.
Along F are a number of points of contact corresponding with those along
C C. These contacts help to work the apparatus, and to insure the perfect
isochronism of the transmitter and receiver. These points of contact,
though insulated one from the other on the surface of the plate, are all
connected underneath with a wire coming from the positive pole of a special
battery. This apparatus requires two batteries, as, in fact, do all
autographic telegraphs--one for sending the current through the selenium,
and one for working the receiver, etc. The different features of this
important plate may, therefore, be summed up thus:

FIGURE 1.

D. Brass rail, grooved and connected with the line wire working the
receiver.

F. Contacts connected underneath with a wire permanently connected with
battery.

C. Contacts connected to insulated wires from selenium.

E. Brass rail, grooved, etc., like D.

RECEIVER.

A small slide, Fig. 2, having at one of its angles a very narrow piece of
brass, separated in the middle by an insulating surface, used for setting
the apparatus in rapid motion. This small slide has at the points, D D, a
small groove fitting into the brass rails of plate, B, Fig. 1, whereby it
can keep parallel on the two brass rails, D and E. Its insulator, B, Fig.
2, corresponds to the insulating interval between F and C, Fig. 1.

A, Fig. 3, circular disk, suspended vertically (made of ebonite or other
insulating material). This disk is fixed. All round the inside of its
circumference are contacts, connected underneath with the corresponding
wires of the receiving apparatus. The wires coming from the seleniumized
plate correspond symmetrically, one after the other, with the contacts of
transmitter. They are connected in the like order with those of disk, A,
and with those of receiver, so that the wire bearing the No. 5 from the
selenium will correspond identically with like contact No. 5 of receiver.

D, Fig. 4, gutta percha or vulcanite insulating plate, through which pass
numerous very fine platinum wires, each corresponding at its point of
contact with those on the circular disk, A.

The receptive plate must be smaller than the plate whereon the light
impinges. The design being thus reduced will be the more perfect from the
dots formed by the passing currents being closer together.

B, zinc or iron or brass plate connected to earth. It comes in contact with
chemically prepared paper, C, where the impression is to take place. It
contributes to the impression by its contact with the chemically prepared
paper.

In E, Fig. 3, at the center of the above described fixed plate is a
metallic axis with small handle. On this axis revolves brass wheel, F, Fig.
5.

[Illustration: FIG. 2]

On handle, E, presses continuously the spring, H, Fig. 3, bringing the
current coming from the selenium line. The cogged wheel in Fig. 5 has at a
certain point of its circumference the sliding spring, O, Fig. 5, intended
to slide as the wheel revolves over the different contacts of disk, A, Fig.
3.

This cogged wheel, Fig. 5, is turned, as in the dial telegraphs, by a rod
working in and out under the successive movements of the electro-magnet,
H, and of the counter spring. By means of this rod (which must be of a
non-metallic material, so as not to divert the motive current), and of an
elbow lever, this alternating movement is transmitted to a catch, G, which
works up and down between the cogs, and answers the same purpose as the
ordinary clock anchor.

[Illustration: FIG. 3]

This cogged wheel is worked by clockwork inclosed between two disks, and
would rotate continuously were it not for the catch, G, working in and out
of the cogs. Through this catch, G, the wheel is dependent on the movement
of electro-magnet. This cogged wheel is a double one, consisting of two
wheels coupled together, exactly similar one with the other, and so fixed
that the cogs of the one correspond with the void between the cogs of the
others. As the catch, G, moves down it frees a cog in first wheel, and both
wheels begin to turn, but the second wheel is immediately checked by catch,
G, and the movement ceases. A catch again works the two wheels, turn half a
cog, and so on. Each wheel contains as many cogs as there are contacts on
transmitter disk, consequently as many as on circular disk, A, Fig. 3, and
on brass disk within camera.

[Illustration: FIG. 4]

[Illustration: FIG. 5]

Having now described the several parts of the apparatus, let us see how it
works. All the contacts correspond one with the other, both on the side of
selenium current and that of the motive current. Let us suppose that the
slide of transmitter is on contact No. 10 for instance; the selenium
current starting from No. 10 reaches contact 10 of rectangular transmitter,
half the slide bearing on this point, as also on the parallel rail,
communicates the current to said rail, thence to line, from the line to
axis of cogged wheel, from axis to contact 10 of circular fixed disk,
and thence to contact 10 of receiver. At each selenium contact of the
rectangular disk there is a corresponding contact to the battery and
electro-magnet. Now, on reaching contact 10 the intermission of the current
has turned the wheel 10 cogs, and so brought the small contact, O, Fig. 5,
on No. 10 of the fixed circular disk.

As may be seen, the synchronism of the apparatus could not be obtained in
a more simple and complete mode--the rectangular transmitter being placed
vertically, and the slide being of a certain weight to its fall from the
first point of contact sufficient to carry it rapidly over the whole length
of this transmitter.

The picture is, therefore, reproduced almost instantaneously; indeed, by
using platinum wires on the receiver connected with the negative pole, by
the incandescence of these wires according to the different degrees of
electricity we can obtain a picture, of a fugitive kind, it is true, but
yet so vivid that the impression on the retina does not fade during the
relatively very brief space of time the slide occupies in traveling over
all the contacts. A Ruhmkorff coil may also be employed for obtaining
sparks in proportion to the current emitted. The apparatus is regulated
in precisely the same way as dial telegraphs, starting always from first
contact. The slide should, therefore, never be removed from the rectangular
disk, whereon it is held by the grooves in the brass rails, into which it
fits with but slight friction, without communicating any current to the
line wires when not placed on points of contact.

* * * * *

[Continued from SUPPLEMENT No. 274, page 4368.]

THE VARIOUS MODES OF TRANSMITTING POWER TO A DISTANCE.

[Footnote: A paper lately read before the Institution of Mechanical
Engineers.]

By ARTHUR ACHARD, of Geneva.

But allowing that the figure of 22 H. P., assumed for this power (the
result in calculating the work with compressed air being 19 H. P.) may be
somewhat incorrect, it is unlikely that this error can be so large that its
correction could reduce the efficiency below 80 per cent. Messrs. Sautter
and Lemonnier, who construct a number of compressors, on being consulted
by the author, have written to say that they always confined themselves in
estimating the power stored in the compressed air, and had never measured
the gross power expended. Compressed air in passing along the pipe, assumed
to be horizontal, which conveys it from the place of production to the
place where it is to be used, experiences by friction a diminution of
pressure, which represents a reduction in the mechanical power stored up,
and consequently a loss of efficiency.

The loss of pressure in question can only be calculated conveniently on the
hypothesis that it is very small, and the general formula,

p1 - p 4L
------- = ---- f(u),
[Delta] D

[TEX: \frac{p_1 - p}{\Delta} = \frac{4L}{D}f(u)]

is employed for the purpose, where D is the diameter of the pipe, assumed
to be uniform, L the length of the pipe, p1 the pressure at the entrance, p
the pressure at the farther end, u the velocity at which the compressed air
travels, [Delta] its specific weight, and f(u) the friction per unit of
length. In proportion as the air loses pressure its speed increases, while
its specific weight diminishes; but the variations in pressure are assumed
to be so small that u and [Delta] may be considered constant. As regards
the quantity f(u), or the friction per unit of length, the natural law
which regulates it is not known, audit can only be expressed by some
empirical formula, which, while according sufficiently nearly with the
facts, is suited for calculation. For this purpose the binomial formula, au
+ bu squared, or the simple formula, b1 u squared, is generally adopted; a b and b1 being
coefficients deduced from experiment. The values, however, which are to
be given to these coefficients are not constant, for they vary with the
diameter of the pipe, and in particular, contrary to formerly received
ideas, they vary according to its internal surface. The uncertainty in this
respect is so great that it is not worth while, with a view to accuracy, to
relinquish the great convenience which the simple formula, b1 u squared, offers.
It would be better from this point of view to endeavor, as has been
suggested, to render this formula more exact by the substitution of a
fractional power in the place of the square, rather than to go through
the long calculations necessitated by the use of the binomial au + bu squared.
Accordingly, making use of the formula b1 u squared, the above equation becomes,

p1 - p 4L
------- = ---- b1 u squared;
[Delta] D

[TEX: \frac{p_1 - p}{\Delta} = \frac{4L}{D} b_1 u^2]

or, introducing the discharge per second, Q, which is the usual figure
supplied, and which is connected with the velocity by the relation, Q =
([pi] D squared u)/4, we have

p1 - p 64 b1
------- = --------- L Q squared.
[Delta] [pi] squared D^5

[TEX: \frac{p_1 - p}{\Delta} = \frac{64 b_1}{\pi^2 D^5} L Q^2]

Generally the pressure, p1, at the entrance is known, and the pressure, p,
has to be found; it is then from p1 that the values of Q and [Delta] are
calculated. In experiments where p1 and p are measured directly, in order
to arrive at the value of the coefficient b1, Q and [Delta] would be
calculated for the mean pressure 1/2(p1 + p). The values given to the
coefficient b1 vary considerably, because, as stated above, it varies with
the diameter, and also with the nature of the material of the pipe. It
is generally admitted that it is independent of the pressure, and it is
probable that within certain limits of pressure this hypothesis is in
accordance with the truth.

D'Aubuisson gives for this case, in his _Traite d'Hydraulique_, a rather
complicated formula, containing a constant deduced from experiment, whose
value, according to a calculation made by the author, is approximately b1 =
0.0003. This constant was determined by taking the mean of experiments made
with tin tubes of 0.0235 meter (15/16 in.), 0.05 meter (2 in.), and 0.10
meter (4 in.) diameter; and it was erroneously assumed that it was correct
for all diameters and all substances.

M. Arson, engineer to the Paris Gas Company, published in 1867, in the
_Memoires de la Societe des Ingenieurs Civils de France_, the results of
some experiments on the loss of pressure in gas when passing through pipes.
He employed cast-iron pipes of the ordinary type. He has represented the
results of his experiments by the binomial formula, au + bu squared, and gives
values for the coefficients a and b, which diminish with an increase in
diameter, but would indicate greater losses of pressure than D'Aubuisson's
formula. M. Deviller, in his _Rapport sur les travaux de percement du
tunnel sous les Alpes_, states that the losses of pressure observed in the
air pipe at the Mont Cenis Tunnel confirm the correctness of D'Aubuisson's
formula; but his reasoning applies to too complicated a formula to be
absolutely convincing.

Quite recently M. E. Stockalper, engineer-in-chief at the northern end of
the St. Gothard Tunnel, has made some experiments on the air conduit of
this tunnel, the results of which he has kindly furnished to the author.
These lead to values for the coefficient b1 appreciably less than that
which is contained implicitly in D'Aubuisson's formula. As he experimented
on a rising pipe, it is necessary to introduce into the formula the
difference of level, h, between the two ends; it then becomes

p1 - p 64 b1
------- = --------- L Q squared + h.
[Delta] [pi] squared D^5

[TEX: \frac{p_1 - p}{\Delta} = \frac{64 b_1}{\pi^2 D^5} L Q^2 + h]

The following are the details of the experiments: First series of
experiments: Conduit consisting of cast or wrought iron pipes, joined by
means of flanges, bolts, and gutta percha rings. D = 0.20 m. (8 in.); L =
4,600 m. (15,100 ft,); h= 26.77 m. (87 ft. 10 in.). 1st experiment: Q =
0.1860 cubic meter (6.57 cubic feet), at a pressure of 1/2(p1 + p), and a
temperature of 22 deg. Cent. (72 deg. Fahr.); p1 = 5.60 atm., p =5.24 atm. Hence p1
- p = 0.36 atm.= 0.36 x 10,334 kilogrammes per square meter (2.116 lb. per
square foot), whence we obtain b1=0.0001697. D'Aubuisson's formula would
have given p1 - p = 0.626 atm.; and M. Arson's would have given p1 - p =
0.9316 atm. 2d experiment: Q = 0.1566 cubic meter (5.53 cubic feet), at a
pressure of 1/2(p1 + p), and a temperature of 22 deg. Cent. (72 deg. Fahr.); p1
= 4.35 atm., p = 4.13 atm. Hence p1 - p = 0.22 atm. = 0.22 X 10,334
kilogrammes per square meter (2,116 lb. per square foot); whence we obtain
b1 = 0.0001816. D'Aubuisson's formula would have given p1 - p = 0.347 atm;
and M. Arson's would have given p1 - p = 0.5382 atm. 3d experiment: Q =
0.1495 cubic meter (5.28 cubic feet) at a pressure of 1/2(p1 + p) and a
temperature 22 deg. Cent. (72 Fahr.); p1 = 3.84 atm., p = 3.65 atm. Hence p1 -
p = 0.19 atm. = 0.19 X 10,334 kilogrammes per square meter (2.116 lb. per
square foot); whence we obtain B1 = 0.0001966. D'Aubuisson's formula would
have given p1 - p = 0.284 atm., and M. Arson's would have given p1 - p =
0.4329 atm. Second series of experiments: Conduit composed of wrought-iron
pipes, with joints as in the first experiments. D = 0.15 meter (6 in.), L
- 0.522 meters (1,712 ft.), h = 3.04 meters (10 ft.) 1st experiments: Q =
0.2005 cubic meter (7.08 cubic feet), at a pressure of 1/2(p1 + p), and a
temperature of 26.5 deg. Cent. (80 deg. Fahr.); p1 = 5.24 atm., p = 5.00 atm. Hence
p1 - p = 0.24 atm. =0.24 x 10,334 kilogrammes per square meter (2,116 lb.
per square foot); whence we obtain b1 = 0.3002275. 2nd experiment: Q =
0.1586 cubic meter (5.6 cubic feet), at a pressure of 1/2(p1 + p), and a
temperature of 26.5 deg. Cent. (80 deg. Fahr.); p1 = 3.650 atm., p = 3.545 atm.
Hence p1 - p = 0.105 atm. = 0.105 x 10,334 kilogrammes per square meter
(2,116 lb. per square foot); whence we obtain b1 = 0.0002255. It is clear
that these experiments give very small values for the coefficient. The
divergence from the results which D'Aubuisson's formula would give is due
to the fact that his formula was determined with very small pipes. It is
probable that the coefficients corresponding to diameters of 0.15 meter
(6 in.) and 0.20 meter (8 in.) for a substance as smooth as tin, would be
still smaller respectively than the figures obtained above.

The divergence from the results obtained by M. Arson's formula does not
arise from a difference in size, as this is taken into account. The author
considers that it may be attributed to the fact that the pipes for the St.
Gothard Tunnel were cast with much greater care than ordinary pipes, which
rendered their surface smoother, and also to the fact that flanged joints
produce much less irregularity in the internal surface than the ordinary
spigot and faucet joints.

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