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of the opposite poles of the magnets, and especially if each maximum be itself determined by the mean of equal deviations on both sides of the maximum; in this case I have frequently determined, at moderate distances, the very point on the cross plank, from whence a line drawn at right angles will pass through the magnets, consequently the nearest possible distance between the magnets and compass. Where the deviations, however, are very small, as it will then require a considerable change in the position of the compass, laterally, to produce any sensible change in the deviation,—the line of direction, or the level, will be proportionally less certain, though the nearest distance may be sufficiently ascertained.
As the person who conducts any experiments on the foregoing principles will have to direct the application of the magnets, with any changes that may be requisite as to their poles or position, whilst the experiment is in progress, an arrangement of directions by signal will be necessary; and this may
very well accomplished by the blows of a hammer or mall.
The distance at which any sound can be heard through solid substances, will depend both on the nature of the concussion, and the quality of the vibrating mass. Through earth, gravel, or other loose materials, the transmission of sound is very limited and uncertain ; but through solid uniform rock, directions may be communicated by signals to very considerable distances. In solid and uniform sandstone, the pick, I understand, may be very well heard through a distance of fifteen or sixteen yards, whilst the vibration produced by a blast may be perceived at very great distances beyond. The working of coal by the pick may be generally heard sixty or eighty feet, I am told ; though no rational determination of the thickness can be made from the nature or intensity of the sound,--for a change in the structure of the bed, or the interposition of an increased quantity of moisture, may produce as great an alteration in the sound as might be expected if the distance were doubled! The blow of a mall upon an iron wedge set in the rock, may be heard much farther than the stroke of a pick, or the blow of the heaviest hammer on the face of the rock,--and this will form a convenient arrangement for the purpose of signals.
VOL. XIIT. NO. XXV.JULY 1832.
By the use of two elements,-number of blows and an extra interval of time in different parts of the series,man abundant code of signals might be arranged within the limits of not more than eight or nine blows in succession *.
* The following may serve as an illustration of the method proposed for signalizing by means of blows. The number might be increased, and the signals modified, by employing scratchings with the point of a pick-axe, which can be heard at considerable distances, as well as by the method of blows.
DIRECTIONS by the EXPERIMENTER ANSWERS or INQUIRIES by the Maobserving the Deviations.
nager of the Magnets. No. of
blows. 2. Attention.
2. We are attending.
where you are; as near as
the floor of the mine.
and apply it to the same
5. They are neutralized. 1, 2. Apply the N. pole of the mag- 1, 2. It is so applied.
net to the middle of the
on the same level. N.B. The
cessive blows. 1,4. Ditto to the extreme right of 1, 4. It is at the extreme right.
the mine; same level. 2, 1. Ditto to the left......so many 2, 1. It is so applied.
yards. 2, 2. Ditto to the extreme left of 2, 2. It is at the extreme left.
the mine. 2, 3. Raise the magnet vertically 2, 3. It is raised as directed.
from the floor, so many feet. 2, 4. Raise it to the roof, directly 2, 4. It is at the roof.
upward. 3, 1. Depress it to the floor, directly 3, 1. It is at the floor.
downward. 3, 2. The experiment is finished. 3, 2. Is the experiment finished ? 3, 3. The experiment is not finished. 3, 3. I understand. 3, 4. Do you understand ?
3, 4. I do not understand. What
do you mean?
And by such a code it would be perfectly easy for the conductor of the experiment to give every requisite direction for the application of the magnets, at any distance to which the blows could be distinctly heard.
At distances, however, beyond the limits of communicable vibrations, the application of the magnets must be by preconcerted arrangement. In this case a certain moment of time might be agreed upon for the application of the magnets; and given intervals arranged when the magnets should be reversed, and when neutralized.
Though, in the preceding investigations, the equal permeability of solid substances generally has been verified or assumed, nothing has yet been stated in respect to the effect of the interposition of metallic iron on the action of the magnet. This substance, the action of which on the magnetic needle is so peculiar, has indeed been made the subject of very particular and diligent investigation, but the results have been intentionally omitted, both because these results are somewhat different from all the others, and because iron, in a metallic state, is not likely to be met with in mining, so as in any way to affect the universality of application of the process herein suggested for the measurement of distances otherwise indeterminable.
Thus much, however, may be briefly mentioned, that iron, in any state in which it can be had, whether malleable or cast, whether in steel tempered or soft, does not prevent the influence of the magnet being transmitted to the compass; but, on the contrary, I have most commonly found, that the deviations produced by the magnet acting through a mass of iron, are greater than when nothing whatever is interposed. I have also found that the influence is not interrupted, though the interposed metal be a mass of hardened steel, nor even when trial was made on a body of powerfully magnetic bars, two or three inches in solid thickness. When the mass of iron is not otherwise magnetic than as to its magnetism of position derived from the earth, then the action of a magnet passed through its neutral or equatorial plane, is, in all cases, (as far at least as can be inferred from very many trials), more energetic than when no such substance is near it. This was so particularly the case when the magnetic influence was passed through the two double cylinders and furnace of a locomotive steam-engine (consisting of ten successive plates of iron, forming a total of 5 inches in thickness of metal), that it required the magnets to be a foot nearer to the compass in free space, than when placed beyond the engine, to produce equal deviations. For, whilst the distance of the magnets and compass, when the influence was transmitted through the engine, was 7 feet 8 inches, the distance on the open side, producing the same deviation, was 6 feet 73 inches
4, 1. Is the magnet against wall ? 4, 1. It is against the wall.
4,3. Yes. It is. 4, 4. No!
4, 4. No. It is not. 1, 2, 1. Lay aside the magnet till di- 1, 2, 1. May we lay aside the magrected.
net ? 1, 2, 2. Place the magnet.
1, 2, 2. Shall we place the magnet ? 1, 2, 3. Which pole of the magnet is 1, 2, 3. The North pole is presented. presented ?
2, 1, 2. The South pole is presented. 2, 1, 3. Where is the magnet placed ? Answer by signal of other column.
ADDITIONAL SIGNALS TO BE FILLED UP.
2, 2, 1; 2, 2, 2; 2, 2, 3; 2, 3, 1; 2, 3, 2; 2, 3, 3; 3, 1, 2; 3, 2, 2; 3, 2, 3; 3, 3, 1; 3, 3, 2; 3, 3, 3; &c.
N. B. The separation of the number of blows by a comma, denotes a sensible pause between each series.
Now this anomaly may be easily shewn to arise from the development of magnetism in the mass of iron, through the proximity of the magnets, by which the direct or permeable influence of the magnet is necessarily augmented; but that the whole of the effect which takes place is not due to this cause,--what is generally called “ induced magnetism,”—but chiefly to the actual transmission of influence through the very substance of the mass of iron, I have distinctly and experimentally determined.
* Some working engineers, who were present when this experiment was made, were exceedingly inquisitive about the effects produced, watching the deviations of the compass with great astonishment. One of them perceiving that the magnet, which was hid from his view by the engine, equally affected the compass as when presented in the open space, addressed himself to his comrade, and made this characteristic remark,-“ Why, Tom,” said he, “ it sees through't!"
A Register of the Date of various Natural Appearances, kept at Treveroux Farm, in the Parish of Limpsfield in Surrey.
By HENRY Cox, Esq. Communicated by W. JACOB, Esq. F. R. S.
May 3. June 5. April 24. May 6. July 5. July 5.
June 18. June 28.
Feb. 25. Feb. 9. April 6. April 19. April 22. April 12. May 10. April 16. April 26. June 16. June 26.
April 15. April 29. June 29. June 25.
April 18. May 15. April 10. April 24. June 12. July 5.