478 Progress of Invention. 



excite permanent polarity in soft iron, an effect which cannot be 

 produced either by touch or by the electric current. It was noticed, 

 at the central workshop of the Nassau Railway, that not only 

 shavings of steel, but even of soft iron, produced in the lathe, were 

 sensibly magnetic, and that, whatever their lengths, they exhibited 

 two poles. It might be supposed that the nature of the polarity 

 would depend on whether the helix formed in this way turned to 

 the right or the left ; but such was not found to be the fact — 

 though, at the same time, the effect seemed to be modified by that 

 circumstance, as, in all those instances in which the spires, looked 

 at from their south pole, were in a direction opposite to that in 

 which the hands of a watch move, the magnetism was stronger than 

 in the others. The relative position of the poles was, however, 

 found to depend on a totally different circumstance ; since the 

 south pole was invariably situated at that extremity where the 

 cut had been commenced ; and the north, at that at which it had 

 terminated. 



New Lens for Photography. — An achromatic lens, which 

 seems to be peculiarly. suited to the purposes of the photographer, 

 is formed by the combination of two concave menisci of crown 

 glass, the focal lengths of which are as one to three, having between 

 them a flint glass lens. The contiguous surfaces are of exactly the 

 same curvature, and therefore are perfectly in contact. Such a 

 lens is found to produce a clean, undistorted picture. It will cover 

 an extent of about 92° ; but it will define well, and illuminate uni- 

 formly an angle of 80°, with a stop one-thirtieth of its focal 

 length; and an angle of 60°, with a stop the one-fifteenth of its 

 focal length. It is less bulky than the ordinary lenses, and must 

 be very durable, since both sides of the flint glass are protected by 

 hard crown glass. 



Rails of Steel and Iron Combined. — Soft iron is objectionable 

 in the rails of railways, on account of its inferior strength and 

 rapid wear ; steel is, generally speaking, too expensive ; but a 

 means has been devised in America, a short time since, of uniting 

 the strength and durability of the one with, to a great extent, the 

 economy of the other. The rail is made, lengthwise, in two por- 

 tions, which, when placed beside each other, and firmly bolted 

 together, leave at the upper edge a longitudinal groove, capable of 

 receiving and holding firmly a bar of steel. If the latter has been 

 inserted before the iron portions have been united, a rail will be 

 obtained in which the parts exposed to the action of the wheels is 

 of steel ; and is not only very durable but, when worn, is capable, 

 with great ease, of being replaced, the remainder of the rail being 

 as available for use as ever. The bar of steel being made to tra- 

 verse the joints of two or more of the compound rails, it binds them 

 together, giving great firmness, and rendering the chances of dis- 

 placement of the rails almost nothing. The iron portions of each 

 rail are so formed, with hollows and corresponding projections, that 

 they cannot slide in any way upon or from each other ; and when 

 all the parts are united, they present an appearance differing but 

 little from that of the ordinary rail. 



