Scientific American Supplement, No. 446, July 19, 1884 by Various
V >>
Various >> Scientific American Supplement, No. 446, July 19, 1884
Pages:
1 |
2 |
3 |
4 | 5 |
6 |
7 |
8 |
9 |
10
Immediately on the cessation of each impulse, the auxiliary battery, E',
again acts to send an impulse of positive polarity through the receiving
paper and stylus in the reverse direction and through the line, L, which
returns to the negative pole of the battery by way of the artificial
resistances, R and R'. Such an impulse, following immediately upon the
interruption of the circuit of the transmitting battery, acts to destroy
the effect of the "tailing" or static discharge of the line, L, upon the
receiving instrument, and also to neutralize the same throughout the
line. By thus opposing the discharge of the line by a reverse current
transmitted directly through the chemical paper, a sharply defined
record will in all cases be obtained; and by transmitting the opposing
impulse through the line, the latter will be placed in a condition to
receive the next succeeding impulse and to record the same as a sharply
defined character.
This arrangement was made on the New York-Cleveland circuit, and the
characters were then clearly defined and of uniform distinctness. The
speed of transmission on this circuit was from 1,000 to 2,000 words per
minute.
Upon the completion of the wire to Chicago, total distance 1,050 miles,
including six miles of No. 8 iron wire through the city, the maximum
speed was found to be 1,200 words per minute, and to my surprise the
speed was not affected by the substitution of an underground conductor
for the overhead wire.
The underground conductor was a No. 16 copper wire weighing 67 pounds
per mile, in a Patterson cable laid through an iron pipe.
I used 150 cells of large Fuller battery on the New York-Chicago
circuit, and afterward with 200 cells in first class condition,
transmitted 1,500 words, or 37,000 impulses, per minute from 49
Broadway, New York, to our test office at Thirty-ninth Street, Chicago.
The matter was always carefully counted, and the utmost care taken to
obtain correct figures.
It may be mentioned as a curious fact that we not only send 1,200 words
per minute through 1,050 miles of overhead wire and five miles of
underground cable, but also through a second conductor in No. 2 cable
back to Thirty-ninth Street, and then connected to a third underground
conductor in No. 1 cable back to Chicago main office, in all about
fifteen miles of underground, through which we sent 1,200 words per
minute and had a splendid margin.--_Electrical World_.
* * * * *
[ELECTRICAL REVIEW].
THEORY OF THE ACTION OF THE CARBON MICROPHONE--WHAT IS IT?
A careful examination of the opinions of scientific men given in the
telephone cases--before Lord McLaren in Edinburgh and before Mr. Justice
Fry in London--leads me to the conclusion that scientific men, at least
those whose opinions I shall quote, are not agreed as to what is the
action of the carbon microphone.
In the Edinburgh case, Sir Frederick Bramwell said: "The variations of
the currents are effected so as to produce with remarkable fidelity the
varied changes which occur, according as the carbon is compressed or
relieved from compression by the gentle impacts of the air set in motion
by the voice."
"The most prominent quality of carbon is its capability, under the most
minute differences of pressure, to enormously increase or decrease the
resistances of the circuit." "That the varying pressure of the black
tension-regulator (Edison's) is sufficient to cause a change in the
conducting power." Sir Frederick also said "he could not believe that
the resistance was varied by a jolting motion; could not conceive a
jolting motion producing variation and difference of pressure, and such
an instrument could not be relied on, and therefore would be practically
useless."
Sir William Thomson, in the same case, said: "The function of the carbon
is to give rise to diminished resistance by pressure; it possesses the
quality of, under slight degrees of pressure, decreasing the resistance
to the passage of the electric current;" and, also, "the jolting motion
would be a make-and-break, and the articulate sounds would be impaired.
There can be no virtue in a speaking telephone having a jolting motion."
"Delicacy of contact is a virtue; looseness of contact is a vice."
"Looseness of contact is a great virtue in Hughes' microphone;" and "the
elements which work advantages in Hughes' are detrimental to the good
working of the articulating instrument."
[Illustration: Fig. 1.]
Mr. Falconer King said: "There would be no advantage in having a jolting
motion; the jolting motion would break the circuit and be a defect in
the speaking telephone," and "you must have pressure and partially
conducting substances."
Professor Fleeming Jenkin said, "The pressure of the carbons is what
favors the transmission of sound."
All the above named scientific men agree that variations of a current
passing through a carbon microphone are produced by _pressure_ of the
carbons against one another, and they also agree that a jolting motion
could not be relied upon to reproduce articulate speech.
Mr. Conrad Cooke said, "The first and most striking principle of Hughes'
microphone is a shaking and variable contact between the two parts
constituting the microphone." "The shaking and variable contact is
produced by the movable portion being effected by sound." "Under Hughes'
system, where gas carbon was used, the instruments could not possibly
work upon the principle of pressure." "I am satisfied that it is not
pressure in the sense of producing a change of resistance." "I do not
think pressure has anything to do with it."
Professor Blyth said: "The Hughes microphone depends essentially upon
the looseness or delicacy of contact." "I have heard articulate speech
with such an instrument without a diaphragm." "There is no doubt that to
a certain extent there must be a change in the number of points of
surface contact when the pencil is moved." "The action of the Hughes
microphone depends more or less upon the looseness or delicacy of the
contact and upon the changes in the number of points of surface contact
when the pencil is moved."
Mr. Oliver Heaviside, in _The Electrician_ of 10th February last,
writes: "There should be no jolting or scraping." "Contacts, though
light, should not be loose."
[Illustration: Fig. 2.]
A writer, who signs "W.E.H.," in _The Electrician_ of 24th February
last, says: "The variation of current arises from a variation of
conductivity between the electrodes, consequent upon the variation of
the closeness or pressure of contact;" and also, "there must be a
variation of pressure between the electrodes when the transmitter is in
action."
It seems, then, that some scientific men agree that variation of
pressure is required to produce action in a microphone, and some of them
admit that a microphone with loose contacts will transmit articulate
speech, while others deny it, and some admit that a jolting or shaking
motion of the parts of the microphone does not interfere with articulate
speech, while others say such motion would break the circuit, and cannot
be relied on.
I will now describe two microphones in which there is a shaking or
jolting motion, and loose contacts, and no variation of pressure of the
carbons against one another, and both of these microphones when used
with an induction coil and battery give most excellent articulation. One
of these microphones is made as follows: Two flat plates of carbon are
secured to a block of cork, insulated from each other; into a hole of
each carbon a pin of carbon fits loosely, projecting above the carbons;
another flat piece of carbon, having two holes in it, bridges over the
two lower carbons, being kept in its place by the pins of carbon which
fit loosely in the holes in it, the bottom carbons being connected with
the battery; a block of cork has a flat side of it cut out so as when
secured to the lower cork the carbons will not come in contact with it,
yet be close enough to it to keep the carbons from falling apart. The
cork covering the carbons forms a dome.
Any good telephone receiver when used in connection with this
microphone, reproduces articulate speech with remarkable distinctness,
especially hissing sounds, and with a loud and full tone.
A description of this microphone was published in _La Lumiere
Electrique_, of 15th April, 1882, and a drawing thereof on 29th April of
same year.
Another form of microphone is made as follows: Two blocks of gas carbon,
C, B, each about one and a half inches long and one inch square, having
each a circular hole one and a quarter inches deep and half inch in
diameter; these two blocks are embedded in a block of cork, C, about
one-quarter of an inch apart, these holes facing each other, each block
forming a terminal of the battery and induction coil; a pencil of
carbon, C, P, about three-eighths of an inch in diameter, and two inches
long, having a ring of ebonite, V, fixed around its center, is placed in
the holes of the two fixed blocks; the ebonite ring fitting loosely in
between the two blocks so as to prevent the pencil from touching the
bottom of the holes in the blocks. The space between the blocks is
closed with wax, W, to exclude the air, but not to touch the ring on the
pencil. A block of cork fitting close to the carbon blocks on all sides
is then firmly secured to the other block of cork. The microphone should
lie horizontally or at a slight angle.
This microphone produces in any good telephone perfect articulation in a
loud and full tone. In these microphones there is certainly "looseness
and delicacy of contact," and there is a "jolting or shaking motion,"
and it does not seem possible that there can be any "pressure of one
carbon against another."
I repeat the question I asked at the beginning of this communication,
and hope that it may elicit from you, or some of our scientific men, an
explanation of the theory of the action of this form of microphone.
W.C. BARNEY.
* * * * *
THE DEMBINSKI MICROPHONIC TELEPHONE TRANSMITTER.
This apparatus, which is shown by Figs. 1, 2, and 3, consists of a
wooden case, A, of oblong shape, closed by a lid fixed by hinges to the
top or one side of the case. The lid is actually a frame for holding a
piece of wire gauze, L L, through which the sound waves from the voice
can pass. In the case a flat shallow box, E F (or several boxes), is
placed, on the lid of which the carbon microphone, D C (Figs. 1 and 3),
which is of the ordinary construction, is placed. The box is of thin
wood, coated inside with petroleum lamp black, for the purpose of
increasing the resonance. It is secured in two lateral slides, fixed to
the case. The bottom of the box is pierced with two openings, resembling
those in a violin (Fig. 2). Lengthwise across the bottom are stretched a
series of brass spiral springs, G G G, which are tuned to a chromatic
scale. On the bottom of the case a similar series of springs, not shown,
are secured. The apparatus is provided with an induction coil, J, which
is connected to the microphone, battery, and telephone receiver (which
may be of any known description) in the usual manner.
[Illustration: Fig. 1.]
The inventors claim that the use of the vibrating springs give to the
transmitter an increased power over those at present in use. They state
that the instrument has given very satisfactory results between Ostende
and Arlon, a distance of 314 kilometers (about 200 miles). It does not
appear, however, that microphones of the ordinary Gower-Bell type, for
example, were tried in competition with the new invention, and in the
absence of such tests the mere fact that very satisfactory results were
obtained over a length of 200 miles proves very little. With reference
to a statement that whistling could be very clearly heard, we may remark
that experience has many times proved that the most indifferent form of
transmitter will almost always respond well and even powerfully to such
forms of vibration.--_Electrical Review_.
[Illustration: Fig. 2.]
[Illustration: Fig. 3.]
* * * * *
NEW GAS LIGHTERS.
We are going to make known to our readers two new styles of electric
lighters whose operation is sure and quick, and the use of which is just
as economical as that of those quasi-incombustible little pieces of wood
that we have been using for some years under the name of matches.
[Illustration: Fig. 1.--MODE OF USING THE GAS LIGHTER.]
The first of these is a portable apparatus designed for lighting gas
burners, and is based upon the calorific properties of the electric
spark produced by the induction bobbin. Its internal arrangement is such
as to permit of its being used with a pile of very limited power and
dimensions. The apparatus has the form of a rod of a length that may be
varied at will, according to the height of the burner to be lighted, and
which terminates at its lower part in an ebonite handle about 4
centimeters in width by 20 in length (Fig. 1). This handle is divided
into two parts, which are shown isolatedly in Fig. 2, and contains the
pile and bobbin. The arrangement of the pile, A, is kept secret, and all
that we can say of it is that zinc and chloride of silver are employed
as a depolarizer. It is hermetically closed, and carries at one of its
extremities a disk, B, and a brass ring, C, attached to its poles and
designed to establish a communication between the pile and bobbin when
the two parts of the apparatus are screwed together. To this end, two
elastic pieces, D and E, fit against B and C and establish a contact. It
is asserted that the pile is capable of being used 25,000 times before
it is necessary to recharge it. H is an ebonite tube that incloses and
protects the induction bobbin, K, whose induced wire communicates on the
one hand with the brass tube, L, and on the other with an insulated
central conductor, M, which terminates at a point very near the
extremity of the brass tube. The currents induced in this wire produce a
series of sparks between the tube, L, and the rod, M, which light the
gas when the extremity of the apparatus is placed in proximity with the
burner.
[Illustration: Fig. 2. MECHANISM OR THE INDUCTION SPARK GAS LIGHTER.]
The ingenious and new part of the system lies in the mode of exciting
the induced currents. When the extremity of the tube, L, is brought near
the gas burner that is to be lighted, it is only necessary to shove the
botton, F, from left to right in order to produce a _limited_ number of
sparks sufficient to effect the lighting. The motion of the button has
not for effect, as might be believed, the closing of the circuit of the
pile upon the inducting circuit of the bobbin. In fact in its normal
position, the vibrator is distant from its contact, and the closing of
the circuit would produce no action. The motion of F produces a
_mechanical_ motion of the spring of the vibrator, which latter acts for
a few instants and produces a certain number of contacts that give rise
to an equal number of sparks. Owing to this arrangement, the expenditure
of electric energy required by each lighting is limited; and, an another
hand, the vibrator, which would be incapable of operating if it had to
be set in motion by the direct current from the pile, can be actuated
_mechanically_. As the motion of the vibrator is derived from the hand
of the operator, and not from the pile, it will be comprehended that the
latter can, everything being equal, produce a larger number of lightings
than an ordinary bobbin and vibrator.
[Illustration: Fig. 3.--INCANDESCENT GAS LIGHTER.]
Dr. Naret's _Fiat Lux_ (Fig. 3) is simpler in its operation, and cheaper
of application, since it takes its current from the ordinary piles that
supply domestic call-bells. It consists essentially of a fine platinum
wire supported by a tilting device in connection with the two poles of a
pile composed of three Leclanche elements. Upon exerting a vertical
pressure on the button placed to the left of the apparatus, either
directly or by means of a cord, we at the same time turn the cock and
cause the platinum spiral to approach, and the latter then becomes
incandescent as a consequence of the closing of the circuit of the pile.
After the burner is lighted it is only necessary to leave the apparatus
to itself. The cock remains open, the spiral recedes from the burner,
the circuit opens anew, and the burner remains lighted until the gas is
turned off. This device, then, is particularly appropriate in all cases
where there is a pressing need of light, for a single maneuver suffices
to open the cock and effect a lighting of the burner.--_La Nature_.
* * * * *
DISTRIBUTION OF HEAT WHICH IS DEVELOPED BY FORGING.
On the 8th of June. 1874, Tresca presented to the French Academy some
considerations respecting the distribution of heat in forging a bar of
platinum, and stated the principal reasons which rendered that metal
especially suitable for the purpose. He subsequently experimented, in a
similar way, with other metals, and finally adopted Senarmont's method
for the study of conductibility. A steel or copper bar was carefully
polished on its lateral faces, and the polished portion covered with a
thin coat of wax. The bar thus prepared was placed under a ram, of known
weight, P, which was raised to a height, H, where it was automatically
released so as to expend upon the bar the whole quantity of work _T=PH,_
between the two equal faces of the ram and the anvil. A single shock
sufficed to melt the wax upon a certain zone and thus to limit, with
great sharpness, the part of the lateral faces which had been raised
during the shock to the temperature of melting wax. Generally the zone
of fusion imitates the area comprised between the two branches of an
equilateral hyperbola, but the fall can be so graduated as to restrict
this zone, which then takes other forms, somewhat different, but always
symmetrical. If A is the area of this zone, b the breadth of the bar, d
the density of the metal, c its capacity for heat, and t-t0 the excess
of the melting temperature of wax over the surrounding temperature, it
is evident that, if we consider A as the base of a horizontal prism
which is raised to the temperature t, the calorific effect may be
expressed by:
Ab x d x C(t-t0);
and on multiplying this quantity of heat by 425 we find, for the value
of its equivalent in work,
T' = 425 AbdC(t-t0).
On comparing T' to T we may consider the experiment as a mechanical
operation, having a minimum of:
T'/T = (425/PH)AbdC(t-t0).
After giving diagrams and tables to illustrate the geometrical
disposition of the areas of fusion, Tresca feels justified in concluding
that the development of heat depends upon the form of the faces and the
intensity of the shock; that the points of greatest heat correspond to
the points of greatest flow of the metal, and that this flow is really
the mechanical phenomenon which gives rise to the calorific phenomenon;
that for action sufficiently energetic and for bars of sufficient
dimensions, about 0.8 of the labor expended on the blow may be found
again in the heat; that the figures formed in the melted wax for shocks
of less intensity furnish a kind of diagram of the distribution of the
heat and of the deformation in the interior of the bar, but that the
calculation of the coefficient of efficiency does not yield satisfactory
results in the case of moderate blows.--_Comptes Rendus_.
* * * * *
TIN IN CANNED FOODS.
[Footnote: Read at an evening meeting of the Pharmaceutical Society,
March 5, 1884.]
By PROFESSOR ATTFIELD, F.R.S., ETC.
From time to time, during the past twelve years, paragraphs have
appeared in newspapers and other periodicals tending in effect to warn
the public at least against the indiscriminate use of canned foods. And
whenever there has been any foundation in fact for such cautions, it has
commonly rested on the alleged presence and harmfulness of tin in the
food. At the worst, the amount of tin present has been absurdly small,
affording an opportunity for one literary representative of medicine to
state that before a man could be seriously affected by the tin, even if
it occurred in the form of a compound of the metal, he would have to
consume at a meal ten pounds of the food containing the largest amount
of tin ever detected.
But the greatest proportions of tin thus referred to are, according to
my experiments, far beyond those ever likely to be actually present in
the food itself in the form of a compound of tin; present, that is to
say, on account of the action of the fluids or juices of the food on the
tin of the can. Such action and such consequent solution of the tin, and
consequent admixture of a possibly assimilable compound of tin with the
food, in my opinion never occurs to an extent which in relation to
health has any significance whatever. The occurrence of tin, not as a
compound, but as the metal itself, is, if possible, still less
important.
During the last fifteen years I have frequently examined canned foods,
not only with respect to the food itself as food, and to the process of
canning, but with regard to the relation of the food to, or the
influence if any of the metal of, the can itself. So lately as within
the past two or three months I have examined sixteen varieties of canned
food for metals, with the following results:
Decimal parts of
a grain of tin
(or other foreign
metal) present in
Name of article a quarter of a lb.
examined.
Salmon none.
Lobsters none.
Oysters 0.004
Sardines none.
Lobster paste none.
Salmon paste none.
Bloater paste 0.002
Potted beef none.
Potted tongue none.
Potted "Strasbourg" none.
Potted ham 0.002
Luncheon tongue 0.003
Apricots 0.007
Pears 0.003
Tomatoes 0.007
Peaches 0.004
These proportions of metal are, I say, undeserving of serious notice. I
question whether they represent more than the amounts of tin we
periodically wear off tin saucepans in preparing food--a month ago I
found a trace of tin in water which had been boiled in a tin kettle--or
the silver we wear off our forks and spoons. There can be little doubt
that we annually pass through our systems a sensible amount of such
metals, metallic compounds, and other substances that do not come under
the denomination of food; but there is no evidence that they ever did or
are ever likely to do harm or occasion us the slightest inconvenience.
Harm is far more likely to come to us from noxious gases in the air we
breathe than from foreign substances in the food we eat.
But whence come the much less minute amounts of tin--still harmless, be
it remembered--which have been stated to be occasionally present in
canned foods? They come from the minute particles of metal chipped off
from the tin sheets in the operations of cutting, bending, or hammering
the parts of the can, or possibly melted off in the operations necessary
for the soldering together of the joints of the can. Some may, perhaps,
be cut, off by the knife in opening a can. At all events I not
unfrequently find such minute particles of metal on carefully washing
the external surfaces of a mass of meat just removed from a can, or on
otherwise properly treating canned food with the object of detecting
such particles. The published processes for the detection of tin in
canned food will not reveal more than the amounts stated in the table,
or about those amounts; that is to say, a few thousandths or perhaps two
or three hundredths of a grain, if this precaution be adopted. If such
care be not observed, the less minute amounts may be found. I did not
detect any metallic particles in the twelve samples of canned food just
mentioned, but during the past few years I have occasionally found small
pieces of metal, perhaps amounting in some of the cases to a few tenths
of a grain per pound. Now and then small shot-like pieces of tin, or
possibly solder, may be met with; but no one has ever found, to my
knowledge, such a quantity of actual metallic tin, tinned iron, or
solder as, from the point of view of health, can have any significance
whatever.
The largest amount of tin I ever detected in actual solution in food was
in some canned soup, containing a good deal of lemon juice. It amounted
to only three-hundredths of a grain in a half pint of the soup as sent
to table. Now, Christison says that quantities of 18 to 44 grains of the
very soluble chloride of tin were required to kill dogs in from one to
four days. Orfila says that several persons on one occasion dressed
their dinner with chloride of tin, mistaking it for salt. One person
would thus take not less than 20 to 30 grains of this soluble compound
of tin. Yet only a little gastric and bowel disturbance followed, and
from this all recovered in a few days. Pereira says that the dose of
chloride of tin as an antispasmodic and stimulant is from 1/16 to 1/2 a
grain repeated two or three times daily. Probably no article of canned
food, not even the most acid fruit, if in a condition in which it can be
eaten, has ever contained, in an ordinary table portion, as much of a
soluble salt of tin as would amount to a harmless or useful medicinal
dose.
Pages:
1 |
2 |
3 |
4 | 5 |
6 |
7 |
8 |
9 |
10