Chapter 4

By making the plungers in two pieces, with a rubber washer or its equivalent between them, we prevent mud or ooze from getting behind and interfering with their working. As the hole in the rubber surrounding the contact-plate, by caused the passage of the pin through it, closes up as soon as the pressure is removed, leaving in the rubber a fault of exceedingly high resistance, the rubber does not require renewing.

In the rubber in which we embedded the contact-plate, we place a layer or more of tinfoil or other easily pierced conducting surface, through which the pin passes on its way to the contact-plate proper. This method we have adopted in order to make the assurance of contact doubly sure.

The grapnel just described we had in use on the Minia since April last. We have tried it severely, and have never known it to fail. No swivel has been used with the rope, in the heart of which is the insulated wire, as it would allow the grapnel to turn over on the bottom, and would be apt to twist and break the wire short off. As a matter of fact, the grapnel will turn, and does turn, with the rope; a swivel is therefore of no value. We are perfectly awake, however, to the fact that a grappling-rope should be made in a manner that will not allow it to kink; and engineers should avail themselves of such rope, especially in deep water. Patents have lately been granted to Messrs. Trott & Hamilton for the invention of a form of rope or cable answering all the requirements of this work.

A small type of grapnel fitted in the manner I have described may be very advantageously used for searching purposes, to ascertain the position either of telegraph or torpedo lines; by towing at a quick rate much time may be saved. The position being ascertained, if it be not desired to lift the cable, the grapnel can be released and hove on board by a tripping line, which can always be attached when such work is contemplated. The great importance of being able to localize an enemy's torpedo lines without raising an alarm will be readily seen by engineers engaged in torpedo work.

REFERENCES TO THE DIAGRAMS.

a, stem of the grapnel containing core; b, flukes; c, recess for insulated contact-plate connected to core; d, covering plate screwed on bottom of grapnel; e, button of plug; f, rubber washer and button; g, metal-plate; h, stem of plug, on which in the under counter-sink, U is a small metal disk which prevents the fittings from fallings out; i, needle; j, spring; k, counter-sink for head of plug; l, counter-sink for spring.

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HUGHES' NEW MAGNETIC BALANCE.

A new magnetic balance has been described before the Royal Society by Prof. D. E. Hughes, F.R.S., which he has devised in the course of carrying out his researches on the differences between different kinds of iron and steel. The instrument is thus described in the _Proceedings of the Royal Society_:

"It consists of a delicate silk-fiber-suspended magnetic needle, 5 cm. in length, its pointer resting near an index having a single fine black line or mark for its zero, the movement of the needle on the other side of zero being limited to 5 mm. by means of two ivory stops or projections.

When the north end of the needle and its index zero are north, the needle rests at its index zero, but the slightest external influence, such as a piece of iron 1 mm. in diameter 10 cm. distant, deflects the needle to the right or left according to the polarity of its magnetism, and with a force proportional to its power. If we place on the opposite side of the needle at the same distance a wire possessing similar polarity and force, the two are equal, and the needle returns to zero; and if we know the magnetic value required to produce a balance, we know the value of both. In order to balance any wire or piece of iron placed in a position east and west, a magnetic compensator is used, consisting of a powerful bar magnet free to revolve upon a central pivot placed at a distance of 30 or more cm., so as to be able to obtain delicate observations. This turns upon an index, the degrees of which are marked for equal degrees of magnetic action upon the needle. A coil of insulated wire, through which a feeble electric current is passing, magnetizes the piece of iron under observation, but, as the coil itself would act upon the needle, this is balanced by an equal and opposing coil on the opposite side, and we are thus enabled to observe the magnetism due to the iron alone. A reversing key, resistance coils, and a Daniell cell are required."

The general design of the instrument, as shown in a somewhat crude form when first exhibited, is given in the figure, where A is the magnetizing coil within which the sample of iron or steel wire to be tested is placed, B the suspended needle, C the compensating coil, and M the magnet used as a compensator, having a scale beneath it divided into quarter degrees.

The idea of employing a magnet as compensator in a magnetic balance is not new, this disposition having been used by Prof. Von Feilitzsch in 1856 in his researches on the magnetizing influence of the current. In Von Feilitzsch's balance, however, the compensating magnet was placed end on to the needle, and its directive action was diminished at will, not by turning it round on its center, but by shifting it to a greater distance along a linear scale below it. The form now given by Hughes to the balance is one of so great compactness and convenience that it will probably prove a most acceptable addition to the resources of the physical laboratory.--_Nature_.

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HOW TO HARDEN CAST IRON.

Cast iron may be hardened as follows: Heat the iron to a cherry red, then sprinkle on it cyanide of potassium and heat to a little above red, then dip. The end of a rod that had been treated in this way could not be cut with a file. Upon breaking off a piece about one-half an inch long, it was found that the hardening had penetrated to the interior, upon which the file made no more impression than upon the surface. The same salt may be used to caseharden wrought iron.

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APPARATUS FOR MEASURING SMALL RESISTANCES.

The accompanying engraving shows a form of Thomson's double bridge, as modified by Kirchhoff and Hausemann. The chief advantage claimed for this instrument consists in the fact that all resistances of defective contact between the piece to be measured and the battery are entirely eliminated--an object of prime importance in measuring very small resistances. By the use of this instrument resistances can be measured accurately down to one-millionth of a Siemens unit.

The general arrangement of the instrument is shown in Fig. 1; Fig. 2 being a diagram of the electrical connections.

The piece of metal to be measured, M, is placed in the measuring forks, gg, in such a manner that the movable fork is removed as far as possible from the stationary one; if the weight of the piece be insufficient to secure a good connection, additional weights may be placed upon it. The main circuit includes the battery, B (Fig. 2), consisting of from two to four Bunsen cells, the key, T, the German silver measuring wire, N, and the piece of metal resting on the forks, all being joined in series. The German silver wire, N, is traversed by two movable knife-edge contacts, cc, as shown. Connections are made between these contacts, cc, the resistance box, the prongs, k and l, of the forks, gg, and the reflecting galvanometer, as shown in Fig. 2. A resistance of ten units is inserted at o and n, while at m and p twenty units or one thousand units are inserted. The positions of cc are then varied until the galvanometer shows no deflection when the key, T, is depressed.

When such is the case, the ratio of resistances n/m is equal to o/p; letting M equal the resistance of the metal bar between the points, h and i, and N equal to the resistance between the points, cc, on the measuring wire, N, then we shall have

M = N (n/m) = N (o/p).

Knowing the cross section in millimeters, Q, of the bar, and observing the temperature, t, in degrees Centigrade, its conductivity, x, as compared with mercury can be determined. If L be the distance, h l or k i, in meters, then

x = (1/m) (L/Q) (1 + at).

For pure metals the value of a may be taken at 0.004; but alloys have a different coefficient. The instrument is made by Siemens and Halske, and is accompanied by a table giving resistances per millimeter of the measuring wire, N.--_Zeitsch. für Elektrotechnik_.

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TERRESTRIAL MAGNETISM.

[Footnote: For a full account of experiments relating to magnetism on railways in New York city, see SCIENTIFIC AMERICAN, January 19,1884.]

_To the Editor of the Scientific American_:

An item has appeared recently in several papers, stating that New York is a highly magnetized city--that the elevated railroad, Brooklyn Bridge cables, etc., are all highly magnetized. As this might convey to the general reader the impression that the magnetism thus exhibited was peculiar to New York city, and as many of your subscribers look anxiously for your answers to numerous questions put for the elucidation of apparent, scientific mysteries, I have thought that perhaps a statement in plain language of experiments made at various times, to elucidate this subject, might, in conjunction with a diagram, serve to explain even to those who have not made a special study of science a few of the interesting phenomena connected with

TERRESTRIAL MAGNETISM.

Some of the first experiments I made, while professor at the Indiana State University, were detailed in the March and August numbers, 1872, of the _Journal_ of the Franklin Institute, and I think showed conclusively that the earth, by induction, renders all articles of iron, steel, or tinned iron magnetic; possessing for the time being polarity, after they have been in a settled position for a short time.

In Dr. I. C. Draper's "Year Book of Nature" for 1873, mention is made of the experiments in which I found every rail of a N. and S. railroad exhibiting polarity.

The same statements were repeated in one of a series of articles sent by me to the _Indianapolis Daily Journal_, dated Jan. 20, 1877, in which I used the following language:

"Every article of iron or steel or tinned iron, by the earth's induction, becomes magnetic. Thus, if we examine our stoves, or a doorlock, or long vertical hinge, or even a high tin cup, by holding a delicate magnetic needle in the hand near those objects, we find the earth has, by induction, attracted to the lower end of the stove utensils, etc., the opposite magnetism from its own; and repelled to the upper end of the stove, etc., the same magnetism which exists in our northern hemisphere. Consequently, the bottom of the stove, or of the hinge, cup, etc., will attract the south (or unmarked end) of our needle; while the top of the stove, etc., attracts the north, or marked end of our magnetic needle. If we apply our needle to the T rails of a N. and S. railroad, we not only find that the lower flange of the rail attracts the S. end of our needle, while the upper flange attracts the N. end of our needle, but we also find, where the two rails come nearly together (say within two inches), that the N. end of the rail attracts the S. end of our needle, while the S. end of the rail attracts the N. (or marked) end of our magnetic needle."

Quite recently, being anxious to see the effect produced on the needle by rails laid E. and W., I experimented on some recently laid here; starting from a S. terminus, in the town of New Harmony, and gradually curving northeast, until the road pursues a due east course to Evansville. There is, however, a branch road of about half a mile, which starts from the Wabash River, at a _west_ terminus, and runs due east to join the other, near where that main track commences its northeast curve. The results (more readily understood by an inspection of the diagram) were as follows:

1. At the south terminus of the railroad, the rails on the east side of the track as well as those on the west side attracted at their south ends the marked end of a small magnetic needle, both at the upper and lower flange; the usual vertical induction being in this case overcome by the greater lateral induction. Whenever, on progressing north, the rails were at least about two inches apart, the upper flange of the north end of any rail would attract the unmarked, while the south end of its neighbor or any other of the north and south laid rails would attract the marked end.

2. The same results were obtained from rails laid all around the northeast curve, and even after they had acquired a due west to east course; showing that each rail acquired the same magnetic polarity which would be exhibited by any magnetic needle oscillating freely in our northern hemisphere, dipping also at its north end considerably downward if suspended at its center of gravity.

3. Applying the needle at the _west_ terminus, a few anomalies were observed; but, especially nearer the junction, the rails all gave the normal result found on the main track.

4. The wheels of the cars standing on the north and south track followed the same law, exhibiting both vertical and lateral induction, so that the lower rims and the forward or north part of the periphery attracted the unmarked end of the needle, while the upper and rear, or south portions of the periphery of the wheel attracted the marked end.

5. The wheels of cars standing on the east and west road exhibited the following modification. The lowest rim of all the wheels, whether standing on the _north_ rails or on the _south_ rails of said track, in consequence of vertical induction attracted the unmarked end of the needle, and the upper rims attracted the marked end of the needle; but the middle portions of the periphery, both anterior and posterior, of the wheels standing on the north rail, attracted the unmarked end, while similar middle portions of wheels standing on south rails attracted the marked end; in consequence of horizontal induction, the wheels being connected by iron axles, and thus presenting considerable extension _across_ the track, viz., from south to north.

Magnetite seems to have acquired its polarity in the same manner, namely by the earth's induction, when the ore contains a large enough percentage of pure iron. A large specimen (6 in. long by 3½ deep and weighing 5½ lb.) which I obtained from near Pilot Knob, Missouri, exhibits polarity, not only at its lateral ends, but also vertically, as the lower surface attracts the unmarked end of a needle, while the plane, which evidently occupied the upper surface in its native bed, attracts the marked end of the needle.

Iron fences invariably exhibit only the polarity by vertical induction; so also small buckets, bells, etc. But in the case of a bell about 3 ft. in diameter at its base, and over two feet deep, tapering to about a foot in diameter at the top, I found that although the top attracted the marked end of the needle, the bottom attracted the unmarked end of the needle only around the northerly half of the circumference, while the southern portion of this lower rim attracted the marked end in consequence of lateral induction, as in N. and S. rails.

Thus, upon a comparison of all these facts, it would appear that, if the magnetism induced by the earth is due to so-called currents of electricity, those currents must be _underneath_ the rails, and must move from west to east, under the south to north rails, and from south to north under the west to east laid rails, as indicated by the arrows in the diagram.

This accords perfectly with what we should theoretically expect, in our northern hemisphere, if the electricity in the earth's crust is due to thermo-electrical currents from east to west, namely, from the more heated to the less heated portion, on any given latitude, while the earth revolves from west to east; as well as also from electrical currents trending from tropical to Arctic regions.

As the network of iron rails spreads from year to year more extensively over our continent, it will be interesting to observe whether or not any effect is produced, meteorological, agricultural, etc., by this diffusion of magnetism.

It may further interest some of your readers to have attention called to facts indicating

SYNCHRONOUS SEISMOLOGY.

The year recently closed furnishes interesting corroborative testimony of an apparent law regarding the propagation of earthquake movements _most readily_ along great circles of our globe, as well as evidence that these seismic movements are frequently transmitted along belts (approximating to great circles) coincident sometimes with continental trends, at other times with fissures which emanate in radii at every 30°, around the pole of the land hemisphere in Switzerland, as described in one of my papers, read at the Montreal meeting of the A.A.A.S.

The terms synchronism or synchronous, as here used, are not designed to imply absolute simultaneity (although that is sometimes the case with disturbances 180° apart), but are rather intended to indicate the tendency presented by these phenomena to exhibit this internal activity, during successive days, weeks, or even months, along a given great circle of the earth, especially one or more of those connected with the land center; perhaps most of all along the great circle which forms the prime vertical, when the center of land is placed at the zenith.

In order to test the above, let us examine the record of the most prominent earthquakes or volcanic eruptions for the year 1883.

Late in Dec., 1882, and early in Feb., 1883, shocks occurred in New Hampshire; on Jan. 11, 1883, also at Cairo, Illinois, and about the same time at Paducah, Ky.; Feb. 27 at Norwich, Conn., and early in Feb. at Murcia, Spain.

These, by examination of any good globe, will be found on a belt forming one and the same great circle of the earth.

Late in March and during part of April the volcano of Ometeke in Lake Nicaragua was active (after being long dormant); Panama, portions of the U.S. of Colombia, and of Chili; also, in May, Helena, M.T.; and, in June, Quito (with Cotopaxi active) were all more or less shaken by earthquakes; and are all found on one belt of a great circle.

The principal record for the remainder of the year comprised:

An earthquake at Tabreez in North Persia, early in May, 1883.

The awful destruction in Ischia, July 29 (with Vesuvius active).

The fearful eruption in the Straits of Sunda, 25th Aug. and later.

Shocks in Sumatra and at Guayaquil, about same date or early in Sept.

Shocks at Dusseldorf, according to a Berlin paper of 5th Sept.

Shocks at Santa Barbara and Los Angeles, early in Sept.

Shocks at Gibraltar and Anatolia in October.

Shocks at Malta, Trieste, and Asia Minor in October.

Azram shaken late in Sept., and great destruction between Scios and Smyrna.

Lastly, the formation of a new island in the Aleutian Archipelago. Date of outburst, early in October, 1883.

Besides these, there were several other less severe disturbances, the records of which are chiefly obtained from Nature, and which will-be referred to below.

If the globe be so placed as to have the land center at the zenith, the exact position of the new island, near Unnok, will be found under the brazen meridian, while Agram, Tabreez, Sunda, Sumatra, Quito, and Guayaquil are all on the prime vertical.

Vesuvius and Hecla were both active early in the year, and they, with the ever restless Stromboli, are situated on the great circle which forms with the land center at Mount Rosa, the radius running S. 30° E., and which would embrace the chief disturbances up to the middle of the year, including as we go north Malta, Sicily, Rome, region of the Po, Bologna, and in the Western Continent, after passing Hecla, Helena in Montana Territory, reaching in Washington Territory and Oregon the belt of it. American volcanoes: Mounts Baker, Rainier, St. Helens, Hood, and Shasta.

Still another seismic belt, starting from the ever active Fogo, and passing through Teneriffe (at that time erupted), would include the regions disturbed in Oct. and Nov., namely, Cadiz, Gibraltar, Malaga (Murcia and Valencia somewhat earlier); it then traversed the center of land, caused the earthquakes at Olmutz in Moravia, and even tremors felt at Irkutsk, as the seismic war moved along said great circle to the volcanic region of S. Japan.

Again, the belt which covers the meridian of land center (about 8°-10° E. long) covers also the region of a disturbanced area in Norway, as well as that portion of Algeria, viz., Bona, in which a mountain 800 meters high, Naiba, is gradually sinking out of sight. About 100 geo. miles E. of Bona is where Graham's Island appeared in the Mediterranean, and a few months later disappeared in deep water.

Another highly seismic belt extends from the volcanoes of Bourbon, N. Madagascar, and Abyssinia to Santoria and the oft disturbed Scios, Smyrna, and Anatolia region; and along the same great circle were shaken Patra in Greece on the 14th Nov., and Bosnia on the 15th; while shocks had been felt at Trieste and Mülhouse about the 11th, and at Styria on the 7th, and disturbances at Dusseldorf in Sept. Finally, on the 28th Dec. S. Hungary (near the confluence of the Drave with the Danube) was visited by seismic movements along this same great circle, which passes through the extinct volcanic region of the Eifel, the oft shaken Comrie in Perthshire, Scotland, the volcanic Iceland, our National Park with its thousands of geysers, the cataclysmic region of Salt Lake and the Wahsatch Mountains (so graphically described by the geologists of the U.S. Geol. Survey), giving rise in Sept. to the earthquakes of Los Angeles and Santa Barbara, and finally reaching the volcanic islands of the Marquesas group.

Thus the seismic efforts of 1883 may be seen to have expended their force partly along the great backbone of the S. and N. American Cordillera, but more especially from the center of land E. and W. along its prime vertical from Sunda to Quito, also southwesterly by the E. coast of Spain, as well as due S. through Algeria, and S. 30° E. through Rome, Naples, Sicily, etc. Finally, the autumnal catastrophes at and near Scios, Anatolia, etc., seem to have been caused by a seismic wave, propagated along the great circle, which often agitates Janina, and produces earthquakes at Agram, where this great circle crosses the prime vertical.

RICHARD OWEN.

New Harmony, Ind., 27 Feb., 1884.

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THE IRON INDUSTRY IN BRAZIL

(PROVINCE OF MINAS GERAES.)

By Prof. P. FERRAND.

Up to the present time, the methods employed in the province of Minas Geraes (Brazil) for obtaining iron permit of manufacturing it direct from the ore without the intervening process of casting. These methods are two in number:

1. The _method by cadinhes_ (crucibles), which is the simpler and requires but little manipulation, but permits of the production of but a small quantity of metal at a time.

2. The _Italian method_, a variation of the Catalan, which requires more skill on the part of the workmen and yields more iron than the preceding.

As these methods seem to me of interest, from the standpoint of their simplicity and easy installation, I propose to describe them briefly, in order to give as faithful and general an _aperçu_ as possible of their application. At present I shall deal with the first one only, the one called the method by _Cadinhes_.

STUDY OF THE METHOD BY CADINHES.