Scientific American Supplement, No. 344, August 5, 1882 by Various
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Various >> Scientific American Supplement, No. 344, August 5, 1882
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When the film is equalized the plate must be detached from the turning
table and placed on a cast iron or tin plate heated to not more than 40°
or 50° C. A gentle heat is quite sufficient to dry the albumen quickly;
a greater heat would spoil it, as it would produce coagulation. So soon
as the film is dry, which will be seen by the iridescent aspect it
assumes, the plate is allowed to cool to the ordinary temperature,
and is then at once exposed either beneath a positive, or beneath an
original drawing the lines of which have been drawn in opaque ink, so as
to completely prevent the luminous rays from passing through them; the
light should only penetrate through the white or transparent ground of
the drawing.
I say a _positive_ because I wish to obtain an engraved plate; if I
wanted to have a plate for typographic printing, I should have to take a
_negative_. After exposure the plate must be at once developed, which is
effected by dissolving in water those parts of the bichromated gelatine
which have been protected from the action of light by the dark spaces
of the cliché; these parts remain soluble, while the others have been
rendered completely insoluble. If the plate were dipped in clear water
it would be difficult to observe the picture coming out, especially on
copper. To overcome this difficulty the water must be tinged with some
aniline color; aniline red or violet, which are soluble in water,
answers the purpose very well. Enough of the dye must be dissolved in
the water to give it a tolerably deep color. So soon as the plate is
plunged into this liquid the albumen not acted on by light is dissolved,
while the insoluble parts are colored by absorbing the dye, so that the
metal is exposed in the lines against a red or violet ground, according
to the color of the dye used.
When the drawing comes out quite perfect, and a complete copy of the
original, the plate with the image on it is allowed to dry either of its
own accord, or by submitting it to a gentle heat. So soon as it is dry
it is etched, and this is done by means of a solution of perchloride
of iron in alcohol. Both alcohol and iron perchloride will coagulate
albumen; their action, therefore, on the image will not be injurious,
since they will harden the remaining albumen still further. But to get
the full benefit of this, the alcohol and the iron perchloride must
both be free from water; it is therefore advisable to use the salt in
crystals which have been thoroughly dried, and the alcohol of a strength
of 95°.
The following is the formula:
Perchloride of iron, well dried 50 gr.
Alcohol at 95° 100 "
This solution must be carefully filtered so as to get rid of any deposit
which may form, and must be preserved in a well-corked bottle, when it
will keep for a long time. The plate is first coated with a varnish of
bitumen of Judea on the edges (if those parts are not already covered
with albumen) and on the back, so that the etching liquid can only act
on the lines to be engraved. It is then placed, with the side to be
engraved downwards, in a porcelain basin, into which a sufficient
quantity of the solution of perchloride of iron is poured, and the
liquid is kept stirred so as to renew the portion which touches the
plate; but care must be taken not to touch with the brush the parts
where there is albumen remaining. The length of time that the etching
must be continued depends on the depth required to be given to
the engraving; generally a quarter of an hour will be found to be
sufficient. Should it be thought desirable to extend the action over
half an hour, the lines will be found to have been very deeply engraved.
When the etching is considered to have been pushed far enough, the plate
must be withdrawn from the solution, and washed in plenty of water;
it must then be forcibly rubbed with a cloth so as to remove all the
albumen, and after it has been polished with a little pumice, the
engraving is complete.
It will be seen that this process may be used with advantage instead of
that of photo-engraving with bitumen, in cases where it is not advisable
to use acids. One of my friends, Mr. Fisch, suggests the plan--which
seems to deserve a careful investigation--of combining this process
with that where bitumen is employed; it would be done somewhat in the
following way. The plate of metal would be first coated evenly with
bitumen of Judea on the turning table, and when the bitumen is quite
dry, it should be again coated with albumen in the manner as described
above. In full sunlight the exposure need not exceed a minute in length;
then the plate would be laid in colored water, dried, and immersed in
spirits of turpentine. The latter will dissolve the bitumen in all
the parts where it has been exposed by the removal of the albumen not
rendered insoluble by the action of light. But it remains to be seen
whether the albumen will not be undermined in this method; therefore,
before recommending the process, it ought to be thoroughly studied. The
metal is now exposed in all the parts that have to be etched, while
all the other parts are protected by a layer of bitumen coated with
coagulated albumen. Hence we may employ as mordant water acidulated with
3, 4, or 5 per cent. of nitric acid, according as it is required to have
the plate etched with greater or less vigor.
By following the directions above given, any one wishing to adopt the
process cannot fail of obtaining good results, One of its greatest
advantages is that it is within the reach of every one engaged in
printing operations.--_Photo News_.
* * * * *
MERIDIAN LINE.
[Footnote: From Proceedings of the Association of County Surveyors of
Ohio, Columbus, January, 1882.]
The following process has been used by the undersigned for many years.
The true meridian can thus be found within one minute of arc:
_Directions_.--Nail a slat to the north side of an upper window--the
higher the better. Let it be 25 feet from the ground or more. Let it
project 3 feet. Kear the end suspend a plumb-bob, and have it swing in a
bucket of water. A lamp set in the window will render the upper part of
the string visible. Place a small table or stand about 20 feet south of
the plumb-bob, and on its south edge stick the small blade of a pocket
knife; place the eye close to the blade, and move the stand so as to
bring the blade, string, and polar star into line. Place the table so
that the star shall be seen very near the slat in the window. Let this
be done half an hour before the greatest elongation of the star. Within
four or five minutes after the first alignment the star will have moved
to the east or west of the string. Slip the table or the knife a little
to one side, and align carefully as before. After a few alignments the
star will move along the string--down, if the elongation is west; up, if
east. On the first of June the eastern elongation occurs about half-past
two in the morning, and as daylight comes on shortly after the
observation is completed, I prefer that time of year. The time of
meridian passage or of the elongation can be found in almost any work on
surveying. Of course the observer should choose a calm night.
In the morning the transit can be ranged with the knife blade and
string, and the proper angle turned off to the left, if the elongation
is east; to the right, if west.
Instead of turning off the angle, as above described, I measure 200 or
300 feet northtward, in the direction of the string, and compute the
offset in feet and inches, set a stake in the ground, and drive a tack
in the usual way.
Suppose the distance is 250 feet and the angle 1° 40', then the offset
will be 7,271 feet, or 7 feet 3¼ inches. A minute of arc at the distance
of 250 feet is seven-eighths of an inch; and this is the most accurate
way, for the vernier will not mark so small a space accurately.
ANGLE OF ELONGATION.
This should be computed by the surveyor for each observation. The
distance between the star and the pole is continually diminishing, and
on January 1, 1882, was 1° 18' 48".
There is a slight annual variation in the distance. July 1, 1882, it
will be 1° 19' 20". If from this latter quantity the observer will
subtract 16" for 1883, and the same quantity for each succeeding year
for the next four or five years, no error so great as one-quarter of a
minute will be made in the position of the meridian as determined in the
summer months. If winter observations are made, the distance in January
should be used. The formula for computing the angle of elongation is
easily made by any one understanding spherical trigonometry, and is
this:
R x sin. Polar dist.
--------------------- = sin. of angle of elongation.
cos. lat.
As an example, suppose the time is July, 1882, and the latitude 40°.
Then the computation being made, the angle will be found to be 1° 43'
34". A difference of six minutes in the latitude will make less than
10" difference in the angle, as one can see by trial. Any good State
or county map will give the latitude to within one or two miles--or
minutes.
The facts being as here stated, the absurdity of the Ohio law,
concerning the establishment of county meridians, becomes apparent. The
longitude has nothing at all to do With the meridian; and a difference
of _six miles_ in latitude makes no appreciable error in the meridian
established as here suggested, whereas the statute requires the latitude
within _one half a second_, which is _fifty feet_. There are some other
things, besides the ways of Providence, which may be said to be "past
finding out." It is not probable that a surveyor would err so much as
_three_ miles in his latitude, but should he do so, then the error in
his meridian line, resulting from the mistake, will be _five seconds_,
and a line _one mile_ long, run on a course 5" out of the way, will vary
but _an inch and a half_ from the true position. Surveyors well know
that no such accuracy is attainable. R. W. McFARLAND,
* * * * *
ELECTRO-MANIA.
By W. MATTIEU WILLIAMS.
A history of electricity, in order to be complete, must include two
distinct and very different subjects: the history of electrical science,
and a history of electrical exaggerations and delusions. The progress of
the first has been followed by a crop of the second from the time when
Kleist, Muschenbroek, and Cuneus endeavored to bottle the supposed
fluid, and in the course of these attempts stumbled upon the "Leyden
jar."
Dr. Lieberkuhn, of Berlin, describes the startling results which he
obtained, or imagined, "when a nail or a piece of brass wire is put into
a small apothecary's phial and electrified." He says that "if, while it
is electrifying, I put my finger or a piece of gold which I hold in my
hand to the nail, I receive a shock which stuns my arms and shoulders."
At about the same date (the middle of the last century), Muschenbroek
stated, in a letter to Réaumur, that, on taking a shock from a thin
glass bowl, "he felt himself struck in his arms, shoulders, and breast,
so that he lost his breath, and was two days before he recovered from
the effects of the blow and the terror" and that he "would not take a
second shock for the kingdom of France." From the description Of the
apparatus, it is evident that this dreadful shock was no stronger than
many of us have taken scores of times for fun, and have given to
our school-follows when we became the proud possessors of our first
electrical machine.
Conjurers, mountebanks, itinerant quacks, and other adventurers operated
throughout Europe, and were found at every country fair and _fete_
displaying the wonders of the invisible agent by giving shocks and
professing to cure all imaginable ailments.
Then came the discoveries of Galvani and Volta, followed by the
demonstrations of Galvani's nephew Aldini, whereby dead animals were
made to display the movements of life, not only by the electricity of
the Voltaic pile, but, as Aldini especially showed, by a transfer of
this mysterious agency from one animal to another.
According to his experiments (that seem to be forgotten by modern
electricians) the galvanometer of the period, a prepared frog, could be
made to kick by connecting its nerve and muscle with muscle and nerve of
a recently killed ox, with, or without metallic intervention.
Thus arose the dogma which still survives in the advertisements of
electrical quacks, that "electricity is life," and the possibility of
reviving the dead was believed by many. Executed criminals were in
active demand; their bodies were expeditiously transferred from the
gallows or scaffold to the operating table, and their dead limbs were
made to struggle and plunge, their eyeballs to roll, and their features
to perpetrate the most horrible contortions by connecting nerves with
one pole, and muscles with the opposite pole of a battery.
The heart was made to beat, and many men of eminence supposed that if
this could be combined with artificial respiration, and kept up for
awhile, the victim of the hangman might be restored, provided the neck
was not broken. Curious tales were loudly whispered concerning gentle
hangings and strange doings at Dr. Brookes's, in Leicester Square, and
at the Hunterian Museum, in Windmill Street, now flourishing as "The
Café de l'Etoile." When a child, I lived about midway between these
celebrated schools of practical anatomy, and well remember the tales of
horror that were recounted concerning them. When Bishop and Williams (no
relation to the writer) were hanged for burking, i.e., murdering people
in order to provide "subjects" for dissection, their bodies were sent to
Windmill Street, and the popular notion was that, being old and faithful
servants of the doctors, they were galvanized to life, and again set up
in their old business.
It is amusing to read some of the treatises on medical galvanism that
were published at about this period, and contrast their positive
statements of cures effected and results anticipated with the position
now attained by electricity as a curative agent.
Then came the brilliant discoveries of Faraday, Ampère, etc.,
demonstrating the relations between electricity and magnetism, and
immediately following them a multitude of patents for electro-motors,
and wild dreams of superseding steam-engines by magneto-electric
machinery.
The following, which I copy from the _Penny Mechanic_, of June 10, 1837,
is curious, and very instructive to those who think of investing in any
of the electric power companies of to-day: "Mr. Thomas Davenport, a
Vermont blacksmith, has discovered a mode of applying magnetic and
electro-magnetic power, which we have good ground for believing will be
of immense importance to the world." This announcement is followed by
reference to Professor Silliman's _American Journal of Science and the
Arts_, for April, 1837, and extracts from American papers, of which the
following is a specimen: "1. We saw a small cylindrical battery, about
nine inches in length, three or four in diameter, produce a magnetic
power of about 300 lb., and which, therefore, we could not move with
our utmost strength. 2. We saw a small wheel, five-and-a-half inches in
diameter, performing more than 600 revolutions in a minute, and lift a
weight of 24 lb. one foot per minute, from the power of a battery of
still smaller dimensions. 3. We saw a model of a locomotive engine
traveling on a circular railroad with immense velocity, and rapidly
ascending an inclined plane of far greater elevation than any hitherto
ascended by steam-power. And these and various other experiments which
we saw, convinced us of the truth of the opinion expressed by Professors
Silliman, Renwick, and others, that the power of machinery may be
increased from this source beyond any assignable limit. It is computed
by these learned men that a circular galvanic battery about three feet
in diameter, with magnets of a proportionable surface, would produce at
least a hundred horse-power; and therefore that two such batteries would
be sufficient to propel ships of the largest class across the Atlantic.
The only materials required to generate and continue this power for
such a voyage would be a few thin sheets of copper and zinc, and a few
gallons of mineral water."
The Faure accumulator is but a very weak affair compared with this, Sir
William Thomson notwithstanding. To render the date of the above fully
appreciable, I may note that three months later the magazine from which
it is quoted was illustrated with a picture of the London and Birmingham
Railway Station displaying a first-class passenger with a box seat on
the roof of the carriage, and followed by an account of the trip to
Boxmoor, the first installment of the London and North-Western Railway.
It tells us that, "the time of starting having arrived, the doors of
the carriages are closed, and, by the assistance of the conductors, the
train is moved on a short distance toward the first bridge, where it
is met by an engine, which conducts it up the inclined plane as far as
Chalk Farm. Between the canal and this spot stands the station-house for
the engines; here, also, are fixed the engines which are to be employed
in drawing the carriages up the inclined plane from Euston Square, by
a rope upwards of a mile in length, the cost of which was upwards of
£400." After describing the next change of engines, in the same matter
of course way as the changing of stage-coach horses, the narrative
proceeds to say that "entering the tunnel from broad daylight to perfect
darkness has an exceedingly novel effect."
I make these parallel quotations for the benefit of those who imagine
that electricity is making such vastly greater strides than other
sources of power. I well remember making this journey to Boxmoor, and
four or five years later traveling on a circular electro-magnetic
railway. Comparing that electric railway with those now exhibiting,
and comparing the Boxmoor trip with the present work of the London and
North-Western Railway, I have no hesitation in affirming that the rate
of progress in electro-locomotion during the last forty years has been
far smaller than that of steam.
The leading fallacy which is urging the electro-maniacs of the present
time to their ruinous investments is the idea that electro-motors
are novelties, and that electric-lighting is in its infancy; while
gas-lighting is regarded as an old, or mature middle-aged business,
and therefore we are to expect a marvelous growth of the infant and no
further progress of the adult.
These excited speculators do not appear to be aware of the fact that
electric-lighting is older than gas-lighting; that Sir Humphry Davy
exhibited the electric light in Albemarle Street, while London was still
dimly lighted by oil-lamps, and long before gas-lighting was attempted
anywhere. The lamp used by Sir Humphry Davy at the Royal Institution, at
the beginning of the present century, was an arrangement of two
carbon pencils, between which was formed the "electric arc" by the
intensely-vivid incandescence and combustion of the particles of carbon
passing between the solid carbon electrodes. The light exhibited by Davy
was incomparably more brilliant than anything that has been lately shown
either in London, or Paris, or at Sydenham. His arc was _four inches
in length_, the carbon pencils were four inches apart, and a broad,
dazzling arch of light bridged the whole space between. The modern arc
lights are but pygmies, mere specks, compared with this; a leap of 1/3
or 1/4 inch constituting their maximum achievement.
Comparing the actual progress of gas and electric lighting, the gas has
achieved by far the greater strides; and this is the case even when we
compare very recent progress.
The improvements connected with gas-making have been steadily
progressive; scarcely a year has passed from the date of Murdoch's
efforts to the present time, without some or many decided steps having
been made. The progress of electric-lighting has been a series of
spasmodic leaps, backward as well as forward.
As an example of stepping backward, I may refer to what the newspapers
have described as the "discoveries" of Mr. Edison, or the use of an
incandescent wire, or stick, or sheet of platinum, or platino-iridium;
or a thread of carbon, of which the "Swan" and other modern lights are
rival modifications.
As far back as 1846 I was engaged in making apparatus and experiments
for the purpose of turning to practical account "King's patent electric
light," the actual inventor of which was a young American, named Starr,
who died in 1847, when about 25 years of age, a victim of overwork
and disappointment in his efforts to perfect this invention and a
magneto-electric machine, intended to supply the power in accordance
with some of the "latest improvements" of 1881 and 1882.
I had a share in this venture, and was very enthusiastic until after I
had become practically acquainted with the subject. We had no difficulty
in obtaining a splendid and perfectly steady light, better than any that
are shown at the Crystal Palace.
We used platinum, and alloys of platinum and iridium, abandoned them as
Edison did more than thirty years later, and then tried a multitude of
forms of carbon, including that which constitutes the last "discovery"
of Mr. Edison, viz., burnt cane. Starr tried this on theoretical
grounds, because cane being coated with silica, he predicted that by
charring it we should obtain a more compact stick or thread, as the
fusion of the silica would hold the carbon particles together. He
finally abandoned this and all the rest in favor of the hard deposit of
carbon which lines the inside of gas-retorts, some specimens of which we
found to be so hard that we required a lapidary's wheel to cut them into
the thin sticks.
Our final wick was a piece of this of square section, and about 1/8 of
an inch across each way. It was mounted between two forceps--one holding
each end, and thus leaving a clear half-inch between. The forceps were
soldered to platinum wires, one of which passed upward through the top
of the barometer tube, expanded into a lamp glass at its upper part.
This wire was sealed to the glass as it passed through. The lower wire
passed down the middle of the tube.
The tube was filled with mercury and inverted over a cup of mercury.
Being 30 inches long up to the bottom of the expanded portion, or lamp
globe, the mercury fell below this and left a Torricellian vacuum there.
One pole of the battery, or dynamo-machine, was connected with the
mercury in the cup, and the other with the upper wire. The stick of
carbon glowed brilliantly, and with perfect steadiness.
I subsequently exhibited this apparatus in the Town-hall of Birmingham,
and many times at the Midland Institute. The only scientific difficulty
connected with this arrangement was that due to a slight volatilization
of the carbon, and its deposition as a brown film upon the lamp glass;
but this difficulty is not insuperable.--_Knowledge_.
* * * * *
ACTION OF MAGNETS UPON THE VOLTAIC ARC.
The action of magnets upon the voltaic arc has been known for a long
time past. Davy even succeeded in influencing the latter powerfully
enough in this way to divide it, and since his time Messrs. Grove and
Quet have studied the effect under different conditions. In 1859, I
myself undertook numerous researches on this subject, and experimented
on the induction spark of the Ruhmkorff coil, the results of these
researches having been published in the last two editions of my notes on
the Ruhmkorff apparatus.
[Illustration: FIG. 1]
These researches were summed up in the journal _La Lumière Electrique_
for June 15, 1879. Recently, Mr. Pilleux has addressed to us some new
experiments on the same subject, made on the voltaic arc produced by a
De Meritens alternating current machine. Naturally, he has found the
same phenomena that I had made known; but he thinks that these new
researches are worthy of interest by reason of the nature of the arc in
which he experimented, and which, according to him, is of a different
nature from all those on which, up to the present time, experiments have
been made. Such a distinction as this, however, merits a discussion.
With the induction spark, magnets have an action only on the aureola
which accompanies the line of fire of the static discharge; and this
aureola, being only a sort of sheath of heated air containing many
particles of metal derived from the rheophores, represents exactly the
voltaic arc.
[Illustration: FIG. 2]
Moreover, although the induced currents developed in the bobbin are
alternately of opposite direction, the galvanometer shows that the
currents that traverse the break are of the same direction, and that
these are direct ones. The reversed currents are, then, arrested during
their passage; and, in order to collect them, it becomes necessary to
considerably diminish the gaseous pressure of the aeriform conductor
interposed in the discharge; to increase its conductivity; or to open to
the current a very resistant metallic derivation. By this latter means,
I have succeeded in isolating, one from the other, in two different
circuits, the direct induced currents and the reversed induced ones.
As only direct currents can, in air at a normal pressure, traverse
the break through which the induction spark passes, the aureola that
surrounds it may be considered as being exactly in the same conditions
as a voltaic arc, and, consequently, as representing an extensible
conductor traversed by a current flowing in a definite direction. Such
a conductor is consequently susceptible of being influenced by all the
external reactions that can be exerted upon a current; only, by reason
of its mobility, the conductor may possibly give way to the action
exerted upon the current traversing it, and undergo deformations that
are in relation with the laws of Ampère. It is in this manner that I
have explained the different forms that the aureola of the induction
spark assumes when it is submitted to the action of a magnet in the
direction of its axial line, or in that of its equatorial line, or
perpendicular to these latter, or upon the magnetic poles themselves.
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