The report was accepted and the resolutions were unanimously adopted. The Board then adjourned sine die.

APPENDIX TO THE REPORT OF THE COMMITTEE.

STATEMENT OF PROFESSOR HENRY IN RELATION TO THE HISTORY OF THE ELECTRO-MAGNETIC TELEGRAPH.

In the beginning of my deposition I was requested to give a sketch of the history of electro-magnetism having a bearing on the telegraph, and the account I then gave from memory I have since critically examined and find it fully corroborated by reference to the original authorities. My sketch, which was the substance of what I had been in the habit of giving in my lectures, was necessarily very concise, and almost exclusively confined to one class of facts, namely, those having a direct bearing on Mr. Morse's invention, and my paper in Silliman's Journal was likewise very brief and intended merely for scientificmen. In order, therefore, to set forth more clearly in what my own improvements consisted it may be proper to give a few additional particulars respecting some points in the progress of discovery, illustrated by wood cuts.

There are several forms of the electrical telegraph: first, that in which frictional electricity has been proposed to produce sparks and : motion of pith balls at a distance.

Second, that in which galvanism has been employed to produce signals by means of bubbles of gas from the decomposition of water. Third, that in which electro-magnetism is the motive power to produce motion at a distance; and again, of the latter there are two kinds of telegraph, those in which the intelligence is indicated by the motion of a magnetic needle, and those in which sounds and permanent signs are made by the attraction of an electro-magnet. The latter is the class to which Mr. Morse's invention belongs. The following is a brief exposition of the several steps which led to this form of the telegraph.

The first essential fact, as I stated in my testimony, which rendered the electro-magnetic telegraph possible was discovered by Oersted, in the winter of 1819-'20. It is illustrated by figure 1, in which the magnetic

Fig. 1.

the wire A B. (See Annals of Philosophy, vol. 16, page 273.)

B

The second fact of importance, discovered in 1820, by Arago and

1

per wire A B, it is

magnetic, it attracts iron filings and not those of copper or brass, and is capable of developing magnetism in soft iron. (See Annales de Chimie, vol. 15, page 94.)

The next important discovery, also made in 1820, by Ampère, was that two wires through which galvanic currents are passing in the same direction attract, and in opposite direction repel, each other. On this fact Ampère founded his celebrated theory, that magnetism onsists merely in the attraction of electrical currents revolving at right angles to the line joining the two poles of the magnet. The magnetisation of a bar of steel or iron, according to this theory, consists in establishing within the metal by induction a series of electrical currents, all revolving in the same direction at right angles to the axis or length of the bar. (See Annales de Chimie, vol. 15, page 69.) It was this theory which led Arago, as he states, to adopt the method of magnetizing sewing needles and pieces of steel wire, shown in

Fig. 3.

figure 3. This method consists in transmitting a current of electricity through a helix For the

surrounding the needle or wire to be magnetized. purpose of insulation the needle was inclosed in a glass tube, and the several turns of the helix were at a distance from each other to insure the passage of electricity, through the whole length of the wire, or, in other words, to prevent it from seeking a shorter passage by cutting across from one spire to another. The helix employed by Arago obviously approximates the arrangement required by the theory of Ampère, in order to develop by induction the magnetism of the iron. By an attentive perusal of the original account of the experiments of Arago, given in the Annales de Chimie et Physique, vol. XV, 1820, page 93, it will be seen that, properly speaking, he made no electromagnet, as has been asserted by Morse and others; his experiments were confined to the magnetism of iron filings, to sewing needles and - pieces of steel wire of the diameter of a millimetre, or of about the thickness of a small knitting needle. (See Annales de Chimie, vol. 15, page 95.)

Mr. Sturgeon, in 1825, made an important step in advance of the experiments of Arago, and produced what is properly known as the electro-magnet. He bent a piece of iron wire into the form of a horseshoe, covered it with varnish to insulate it, and surrounded it with a helix, of which the spires were at a distance. When a current of galvanism was passed through the helix from a small battery of a single cup the iron wire became magnetic, and continued so during the passage of the current. When the current was interrupted the magnetism disappeared, and thus was produced the first temporary soft iron magnet.

The electro-magnet of Sturgeon is shown in figure 4, which is an exact copy from the drawing in the Transactions of the Society for the Encouragement of Arts, &c., vol. XLIII. By comparing figures 3 and 4 it will be seen that the helix employed by Sturgeon was of the same kind as that used by Arago; instead, however, of e straight, steel wire inclosed in a tube of

Fig. 4.

glass, the former employed a bent wire of soft iron. The difference in the arrangement at first sight might appear to be small, but the difference in the results produced was important, since the temporary magnetism developed in the arrangement of Sturgeon was sufficient to support a weight of several pounds, and an instrument was thus produced of value in future research.

The next improvement was made by myself. After reading an account of the galvanometer of Schweigger, the idea occurred to me that a much nearer approximation to the requirements of the theory of Ampère could be attained by insulating the conducting wire itself, instead of the rod to be magnetized, and by covering the whole surface of the iron with a series of coils in close contact. This was effected by insulating a long wire with silk thread, and winding this around the rod of iron in close coils from one end to the other. The same principle was extended by employing a still longer insulated wire, and winding several strata of this over the first, care being taken to insure the insulation between each stratum by a covering of silk ribbon. By this arrangement the rod was surrounded by a compound helix formed of a long wire of many coils, instead of a single helix of a few coils, (figure 5.)

Fig. 5.

n

In the arrangement of Arago and Sturgeon the several turns of wire were not precisely at right angles to the axis of the rod, as they should be, to produce the effect required by the theory, but slightly oblique, and therefore each tended to develop a separate magnetism not coincident with the axis of the bar. But in winding the wire over itself the obliquity of the several turns compensated each other, and the resultant action was at right angles to the bar. The arrangement then introduced by myself was superior to those of Arago and Sturgeon, first in the greater multiplicity of turns of wire, and second in the better application of these turns to the development of magnetism. The power of the instrument, with the same amount of galvanic force, was by this arrangement several times increased. The maximum effect, however, with this arrangement and a single battery was not yet obtained. After a certain length of wire had been coiled upon the iron the power diminished with a further increase of the number of turns. This was due to the increased resistance which the longer wire offered to the conduction of electricity. Two methods of improvement therefore suggested themselves. The first consisted, not in increasing the length of the coil, but in using a number of separate coils on the same piece of iron. By this arrangement the resistance to the conduction of the electricity was diminished and a greater quantity made to circulate around the iron from the same battery. The second method of producing a similar result consisted in increasing the number of elements of the battery, or, in other words, the projectile force of the electricity, which enabled it to pass through an increased number of turns of wire, and thus, by increasing the length of the wire, to develop the maximum power of the iron.

Fig. 6.

To test these principles on a larger scale the experimental magnet was constructed, which is shown in figure 6. In this a number of compound helices were placed on the same bar, their ends left projecting, and so numbered that they could be all united into one long helix, or va

riously combined in sets of lessser length.

From a series of experiments with this and other magnets it was proved that, in order to produce the greatest amount of magnetism. from a battery of a single cup, a number of helices is required; but when a compound battery is used then one long wire must be employed, making many turns around the iron, the length of wire and

consequently the number of turns being commensurate with the projectile power of the battery.

In describing the results of my experiments the terms intensity and quantity magnets were introduced to avoid circumlocution, and were intended to be used merely in a technical sense. By the intensity magnet I designated a piece of soft iron, so surrounded with wire that its magnetic power could be called into operation by an intensity battery, and by a quantity magnet, a piece of iron so surrounded by a number of separate coils that its magnetism could be fully developed by a quantity battery.

I was the first to point out this connexion of the two kinds of the battery with the two forms of the magnet in my paper in Silliman's Journal, January 1831, and clearly to state that when magnetism was to be developed by means of a compound battery, one long coil was to be employed, and when the maximum effect was to be produced by a single battery, a number of single strands were to be used.

These steps in the advance of electro-magnetism though small, were such as to interest and astonish the scientific world. With the same

battery used by Mr. Sturgeon, at least a hundred times more magnetism was produced than could have been obtained by his experiment. The developments were considered at the time of much importance in a scientific point of view, and they subsequently furnished the means by which magneto-electricity, the phenomena of dia magnetism, and the magnetic effects on polarized light were discovered. They gave rise to the various forms of electro-magnetic machines which have since exercised the ingenuity of inventors in every part of the world, and were of immediate applicability in the introduction of the magnet to telegraphic purposes. Neither the electro-magnet of Sturgeon nor any electro-magnet ever made previous to my investigations wag applicable to transmitting power to a distance.

The principles I have developed were properly appreciated by the scientific mind of Dr. Gale, and applied by him to operate Mr. Morse's machine at a distance.

Previous to my investigations the means of developing magnetism in soft iron were imperfectly understood. The electro-magnet made by Sturgeon, and copied by Dana, of New York, was an imperfect quantity magnet, the feeble power of which was developed by a single battery. It was entirely inapplicable to a long circuit with an intensity battery, and no person possessing the requisite scientific know