TRANSACTIONS OP THE SECTIONS. 23 



By turning the lower wheel by a suitable key, the cylinders may be moved up and 

 down within the spirals. Two steel bar magnets are arranged to an astatic system, 

 connected together by a rigid brass junction, and suspended so that both magnets 

 are in the same horizontal plane. It is so arranged that these two magnets have the 

 two spirals between them, and have their poles opposite to the centre of the spirals. 

 When, therefore, a current is sent through the spirals, it exerts no more action on 

 the magnets than the centre or neutral point of a magnet would do. Supposing the 

 bai's within the spirals to be also perfectly central, they also present their neutral 

 points to the magnetic poles, and hence exert no action upon it. But if the key be 

 turned so as to bring the two ends of the diamagnetic bars to act upon the suspended 

 magnets, if the bars be polar, the magnitude and nature of their polarity will be indi- 

 cated by the consequent deflection of the magnets. The index by which the deflec- 

 tion of the magnets is observed is a ray of light reflected from a mirror attached to 

 the magnets ; and as the length of this ray may be varied at pleasure, the sensibihty 

 of the instrument may be indefinitely increased. When cylinders of bismuth are 

 submitted to experiment, a very marked deflection is produced, indicating a polarity 

 on the part of the bismuth opposed to the polarity of iron. This is the result ahead j' 

 obtained by M. Weber ; but against it, it has been urged that the deflection is due 

 to induced currents excited in the metalhc cylinders during their motion within the 

 spirals. To this objection Prof. Tyndall replied as follows: — first, the deflection 

 produced was a permanent deflection, which could not be the case if it were due to 

 the momentary currents of induction ; secondly, if due to induction, copper ought 

 to show the effect far more energetically than bismuth, for its conducting power and,, 

 consequently, the facility with which such currents are produced, is fifty times 

 greater than that of bismuth ; but with cylinders of copper no sensible deflection 

 was produced; thirdly, two prisms of the heavy glass with which Mr. Faraday 

 discovered the diamagnetic force and produced the rotation of the plane of polariza- 

 tion of a luminous ray, were substituted for the metallic cylinders ; and although the 

 action was far less energetic, it was equally certain as in the case of bismuth, and 

 indicated the same polarity. The formation of induced currents is wholly out of 

 the question here, for the substance is an insulator. The experiments, therefore, 

 remove the last remaining doubt from the proposition, that diamagnetic bodies under 

 magnetic excitement possess a polarity which is the reverse of that possessed by 

 magnetic ones. 



Experimental Observations on an Electric Cable. 

 By WiLDMAN Whitehouse. 



After referring to the rapid progress in submarine telegraphy which the last 

 four years have witnessed, Mr. Whitehouse said that he regarded it as an esta- 

 blished fact, that the nautical and engineering difficulties which at first existed had 

 been already overcome, and that the experience gained in submerging the shorter 

 lengths had enabled the projectors to provide for all contingencies affecting the 

 greater. The author then drew the attention of the Section to a series of experi- 

 mental observations which he had recently made upon the Mediterranean and 

 Newfoundland cables, before they sailed for their respective destinations. These 

 cables contained an aggregate of 1125 miles of insulated electric wire, and the 

 experiments were conducted chiefly with reference to the problem of the practica- 

 bility of establishing electric communications with India, Australia, and America. 

 The results of all the experiments were recorded by a steel style upon electro- 

 chemical paper by the action of the current itself, while the paper was at the same 

 time divided into seconds and fractional parts of a second by the use of a pendulum. 

 This mode of operating admits of great delicacy in the determination of the results, 

 as the seconds can afterwards be divided into hundredths by the use of a " vernier," 

 and the result read off with the same facility as a barometric observation. Enlarged 

 fac-similes of the electric autographs, as the author calls them, were exhibited as 

 diagrams, and the actual slips of electro-chemical paper were laid upon the table. 

 The well-known effects of induction upon the current were accurately displayed ; 

 and contrasted with these were other autographs showing the effect of forcibly dis- 

 charging the wire by giving it an adequate charge of the opposite electricity in the 



