22 
SCIENCE. 
ON THE DYNAMO-ELECTRIC CURRENT AND 
ON CERTAIN MEANS TO IMPROVE ITS 
STEADINESS. 
BY C. WILLIAM SIEMENS, D.C.L., F.R.S. 
The author, after alluding to the early conception by Dr. 
Werner Siemens of the dynamo-electric or accumulative 
principle of generating currents, makes reference to the 
two papers on the subject presented, the one by Sir Charles 
Wheatstone and the other by himself, to the Royal Society 
in February, 1867. The machine then designed by him, 
and shown in operation on that occasion, is again brought 
forward with a view of indicating the progress that has 
since taken place in the construction of dynamo-electrical 
machines, particularly those by Gramme and Siemens von 
Alteneck. The paper next points out certain drawbacks 
to the use of these machines, both of them being subject to 
the disadvantage that an increase of external resistance 
causes a falling off of the current; and that, on the other 
hand, the short circuiting of the outer resistance, through 
contact between the carbon electrodes of an electric lamp, 
very much increases the electric excitement of the machine, 
and the power necessary to maintain its motion, giving rise 
to rapid heating and destructive sparks in the machine 
itself. 
An observation in Sir Charles Wheatstone’s paper is re- 
ferred to, pointing to the fact that a powerful current is set 
up in the shunt circuit of a dynamo-electric machine, 
which circumstance has then been taken advantage of to 
some extent by Mr. Ladd and Mr. Brush, in constructing 
current generators. 
The principal object of the paper is to establish the con- 
ditions under which dynamo-electric machines worked on 
the shunt principle can be made to give maximum results. 
A series of tables and diagrams are given, the results of 
experiments conducted by Mr. Lauckert, electrician, em- 
ployed at the author’s works, which lead up to the conclu- 
sion that, in constructing such machines on the shunt prin- 
ciple, the resistance on the rotating helix has to be consid- 
erably reduced by increasing the thickness of the wire 
employed, and that on the magnets has to be increased 
more than tenfold, not by the employment of thin wire, but 
by augmenting the length and weight of coil wire em- 
ployed. 
The results of this mode of distributing the resistances is 
summarized as follows : 
1. That the electro-motive force, instead of diminishing 
with increased resistance, increases at first rapidly, and 
then more slowly towards an asymptote. 
2. That the current in the outer circuit is actually greater 
for a unit and a half resistance than for one unit. 
3. With an external resistance of one unit, which is about 
equivalent to an electric arc, when thirty or forty webers are 
passing through it, 2.44 horse power is expended, of which 
1.29 horse power is usefully employed, proving an efficiency 
of 53 per cent., as compared with 45 per cent, in the case of 
the ordinary dynamo-machine. 
4. That the maximum energy which can be demanded 
from the engine is 2.6 horse power, so that but a small mar- 
gin of power is needed to suffice for the greatest possible 
requirement. 
5. That the maximum energy which can be injuriously 
transformed into heat in the machine itself is 1.3 horse 
power, so that there is no fear here of destroying the insula- 
tion of the helix by excessive heating. 
6. That the maximum current is approximately that which 
would be habitually used, and which the commutator and 
collecting brushes are quite capable of transmitting. 
Hence the author concludes that the new machine will 
give a steadier light than the old one, with greater average 
economy of power ; that it will be less liable to derange- 
ment, and may be driven without variation of speed by a 
smaller engine ; also that the new machine is free from all 
objection when used for the purposes of electro-deposition. 
This construction of machine enables the author to effect 
an important simplification of the regulator to work electric 
lamps, enabling him to dispense with all wheel and clock 
work in the arrangement. The two carbons being pushed 
onward by gravity or spring power, are checked laterally by 
apointed metallic abutment situated at such a distance from 
the arc itself, that the heat is only just sufficient to cause the 
gradual wasting away of the carbon in contact with atmos- 
pheric air. The carbon holders are connected at the iron 
core of a solenoid coil, of a resistance equal to about fifty 
times that of the arc, the ends of which coil are connected to 
the two electrodes respectively. The weight of the core 
(which may be varied) determines the force of the current 
that has to pass through the regulating coil in order to keep 
the weight in suspension, and this in its turn is dependent 
upon the resistance of the arc. The result is that the length 
of the arc is regulated automatically, so as to maintain a 
uniform resistance signifying uniform development of light. 
— E ng ineering. 
THE HELIOGRAPH. 
The English Government is again indebted to the Helio- 
graph for (he receipt of an important dispatch received 
from the seat of war in Afghanistan, announcing the result 
of an attack on British troops, in which their enemy suffered 
severely. The message is dated Camp Ghuzni, April 22d, 
and was received in London on the following day. 
The value of the heliograph in war operations is becom- 
ing more apparent every day ; in this instance the message 
probably could not have been delivered so speedily by 
electric telegraph. The Heliograph does not require the 
route to be kept open. The line of communication can not 
be cut, for the simple reason that the signalling takes place 
over the heads of the enemy, and the stations required are 
few and far between. — A ten inch mirror, and this is the size 
of the ordinary field heliograph, is capable of reflecting the 
sun’s rays in the form of a bright spot or flare to a distance 
of fifty miles, the signal at this interval being recognizable 
without the aid of a glass. That is to say two*trained 
sappers, each provided with a mirror can readily speak to 
one another, supposing the sun is shining, within a interval 
of fifty miles between them, provided their stations are 
sufficiently high, and no rising ground intervenes to stop 
the rays. The adjustment of the military heliograph is a 
very simple matter. — An army leaves its base where a 
heliograph station is located, and after travelling some 
miles desires to communicate with those they have left. A 
hill in the locality is chosen and a sapper ascends with his 
heliograph, which is simply a stand bearing a mirror, swung 
like the ordinary toilet glass, except that besides swinging 
horizontally, it is also piovoted, so as to also move ver- 
tically. Behind the mirror in the very centre, a little of the 
quicksilver is removed, so that the sapper cango.behind 
the instrument and look through a tiny hole in it towards 
the station he desires to signal. 
Having sighted the station by adjusting the mirror, he 
next proceeds to set up in front of the heliograph a rod, and 
upon this rod is a movable stud. This stud is manipu- 
lated like the foresight of a rifle, and the sapper, again standing 
before his instrument, directs the adjustment of the stud, 
until the hole in the mirror, the stud, and the distant station 
are in line. The heliograph is then ready to work, and in 
order to flash signals, so that they may be seen at a distance, 
the sapper has only to take care that his mirror reflects the 
sunshine, on the stud just in front of him. 
A WONDERFUL METEOR. 
Macon, Ga., June 30, 1880. 
At about twelve o’clock last night a meteor as large as a 
barrel, starting trom the zenith, plunged down the north- 
eastern sky and exploded near here with a report that 
reverbrated for thirty seconds and shook the earth even at 
this point. The meteor was about five seconds in falling, 
during which time the city was lit up as though by a power- 
ful electric light. Much excitement prevailed in the negro 
quarter — the inhabitants rushing into their houses, closing 
the doors and filling the air with screams and prayers. 
The time between the disappearance of the phenomenon 
and the report was about three minutes. This would make 
the distance from Macon about forty miles. 
