PROCEEDINGS OP THE POLYTECHNIC ASSOCIATION. 551 



out of order — as all galvanic batteries sometimes are — refuses to 

 produce the usual results ; the steel magnet being the producer 

 of electricity, gives this in a constant form, as those magnets, if 

 well made, are always the same and never lose their power, as 

 almost every one knows. 



My first construction is this : two straight cylindrical steel 

 bars of about one foot long, each composed of three, five, or 

 seven flat bars, secured parallel together with screws, and after- 

 wards turned cylindrical, are as strong as possible magnetized, 

 and is inclosed in a glass tube of the same length, and open at 

 both ends ; around this a coil is wound for the whole length, how- 

 ever, in such a way that the winding is the thickest where the 

 greatest" magnetic intensity resides, that is towards the poles ; 

 towards the middle or neutral part of the bars the layer of coil 

 is only thinly covering the bars. Those thus coiled, magnets 

 are secured in a horizontal and parallel position, on a wooden 

 basis, one at each side, equal distant and parallel to a horizontal 

 axis which is a little longer than the bars; at each extremity of 

 the axis is attached a keeper, at right angles and at such a dis- 

 tance that by turning the axis the keepers pass with their ends, 

 very closely along the extremities of the steel magnets, which of 

 course lay with the opposite poles towards the same keepers. It 

 is clear that this arrangement works like the double of the appa- 

 ratus, number 11, above, and has besides the advantage of all 

 the magnetic surface of the steel magnets, being made available 

 by the coil. 



13. The second construction based on this principle, has been 

 made by me, however, on a small scale only ; it is so different in 

 appearance and the manner of its operation from the former, that 

 it may be considered by some, an altogether different apparatus; 

 it only requires to be made of large size to produce powerful ef- 

 fects, perhaps surpassing number 12, above. 



It consists of two strong horseshoe magnets, of polished steel, 

 with cylindrical extremities, lying on a horizontal base and 

 touching each other with their opposite poles, which are situated 

 in a coil of fine, well isolated copper wire, immovably fixed to 

 the said base ; the magnets may slide in and out the two coils, 

 if now by means of a lever the poles of the two horseshoe mag- 

 nets are suddenly separated inside the coils to the distance of ^ 

 to I inch, their magnetism made latent by the contact, is sud- 

 denly set free, and they induce an electric current in the coils ; 



