The second of Mr. J, D. Bishop's course of lectures on Magnetisin and Electromagnetism was delivered in the Masonie Hall on the 24th ultimo, There was a fair attendance, and the audi-once were able, notwithstanding the coldness of the night, to sit out the lecture without the least discomfort, from the care which had been taken to heat the hall for the occasion. The experimental apparatus also placed so as to be in full view. Atter some reference to the discovery of the principle of B-magnetism, the lecturer proceeded to illustrate his subject by shawm the properties of artificially maynetised metal in bars of soft iron and the usual horse-shoe shaped piece of steel. The soft iron admitted of magnetisation from the battery in a very high degree, losing its power, however, when removed from its envelope of inductive wire evil. In a variety of ways the different effects of the current, the changes of polarity which could be brought about, the attraction and repulsion of the metals, and their sympathetic power, when magnetised, over the needle, were fully illustrated by experiments. The lecturer also showed that while electricity was used to produce magnetism, the latter might also be used to induce electricity, which he proved by p ing w magnetised bar inside the conduct it coil, though not in direct contact, and, severing the connection with the battery, atle: ing the magnetic needle, as on a telegraph dial, in the' same manner as from the battery. Rejoining the electro-magnetic machine with which he was operating to the battery wires, the lecturer then, by breaking the current, so as to cause a vibratory motion, and the magnetic bar to be attracted and relieved with great rapidity, created assort of magnetic harmonicon, with considerable range of notedependant upon the speed of the motion referred to. Passing to practical applications of the theory, the lecturer drew the attention of his audience toa couple of time-balls, placed in conspicuous positions against the wall, and connected by a wire with an electric timepiece. These balls were timed to fall at ten o'clock, but unfortunately some unnoticed shifting of the wire prevented the experiment from succeeding with both, the at the hotir fixed one of them dropped from its perch. A second essay resulted similarly, except that the one which formerly refused to come down was the one which now dropped. The principle, however, was rendered sufficiently clear, though we doubt if in practice it would not be found less useful than the gun-tire" system, by Which residents at present regulate their horologues. Placed, for instance, as the lecturer suggested, on Reynolds' Tower, the falling of the time-ball would be an event to be looked for with a special effort of memory and observation, while the ti gun forces its announcement upon public attention. The time-ball may perhaps considered to be less a medium by which to advise the regulation of time-keepers in detail, as of public clocks in large centres, and in cities where the time-gun unless situated ina commanding position, as on the Castle-hill of Edinburgh, would be little likely to command attention. The appli tion of electro-magnetism as a motive power was also interestingly exhibited, but the lecturer explained that its application on an extensive scale was restricted by the cost of the metals—zine being relatively four times the cost of coal, Still, the lecturer held out some inducement to the curious and ingenious to employ electricity as a motor, by saying that power suicient to grind coffee might be got up for $24. Another practical application of vital interest was the electric fire-alarm. By means of electric wires distributed over a house, and communicating with an alarm bell, the occurrence of fire, anywhere from garret to cellar, is, through the excitement produced on the wire at a temperature of from 200° Fah. upwards, telegraphed to the bell. Phe experiment was not done with the deliberation which would have been advi ble to recommend the use of the alarm, the degree of heat suggesting that a dangerous conflagration must be going on before intimation would be given by the monitor. But we believe that, had it not been for Mr. Bishop's desire to avoid delay in his programme, a more gradual raising of the heat, would have demonstrated still Detter the etlicacy of the alarm, As it was, the warning note soon rung forth when a slight flame under the' model excited the magnetic current. Coming to the last but not least interesting part of his programme, Mr. Bishop indulged his audience with a spirit-rapping seanc After evolving responsive raps. from spi in answer to some amusing quen them, he in the first place laid thi ones, and then, in accordance with al wish, dispelled the illusion by explain ing and exhibiting the cause of so myster rious an effect. This wse nothing more an_ application of by wires from the battery, cunning: ly comtntinicated through two legs of the very matter-of-fact-looking table used, to a hammer which, by a pre-arrangement of the operator with his assistant, struck responses adapted to the course of his enquiries at the or:
Mr. Bishop's experiments were frequent ly applauded during the evening, and afforded much gratification, We have little doubt that on the next occasion a larger if not a more appreciative house will encourage the lecturer.
Text read from the printed page and cleaned; old type leaves the occasional error.