350 Mr. Stagg on the prevention of Explosions in Collieries. 



of mine had a steel horse-shoe made, weighing thirty-four 

 pounds, of one piece. It was magnetized to saturation by one 

 single passage througii a cylinder constructed purposely for 

 this experiment ; and a second magnet, after having been placed 

 reversed in the cylinder, proved sufficient to change the poles 

 without having lost its suspending power. Besides the faci- 

 lity and rapidity of this method, it has moreover the advan- 

 tage, that a bar magnetized in this manner cannot possibly 

 have intermediate poles ; and if it previously had possessed any 

 they disappear instantly in the magnetizing cylinder. 



This mode is nothing more than the double passing of Du- 

 hamel or Mitchell, only by means of galvanism, and far more 

 powerful, easy and certain. As in the double passing the op- 

 posite poles of the magnet employed must be kept close toge- 

 ther, so as to exert successively their greatest action upon each 

 small part of the bar to be magnetized, in like manner I make 

 my cylinder quite short, that each portion of the bar may ex- 

 perience the entire force of the voltaic element. 



My friend Dr. Munnich publicly repeated my experiments 

 with the magnetizing cylinder at a meeting of the Utrecht So- 

 ciety of Naturalists; and the Faculty of the Physical Sciences 

 which was present was convinced of the efficiency of the 

 method. On this occasion he increased considerably the in- 

 tensity of some very powerful bars belonging to the collection, 

 and which had been magnetized by Knight himself, reversed 

 their poles by a single passage, &c. 

 Haarlem, March 7, 1844. 



LX. Jlemarks relative to the Prevention of Explosions in Col- 

 lieries. By J. D. Stagg, Esq. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



^^HE recent and very lamentable accident at Haswell Col- 

 liery (near Durham), whereby no less than ninety-five 

 of our fellow-creatures were hurried into eternity, must occa- 

 sion but one universal feeling of sorrow that such awful cata- 

 strophes cannot yet be prevented. 



When we further consider the consequent misery of the 

 surviving relatives, and the prospect that we are not in pos- 

 session of any means of effi2Ctually guarding against the recur- 

 rence of such a fearful loss of human life, it should stimulate 

 us to increased care in the working of collieries, and to endea- 

 vours to prevent the possibility of such events. 



I am not practically acquainted with the winning of coal, 

 but I beg to bring before the attention of better informed par- 



