It certainly cannot be said that the American electrician has as yet demonstrated the incorrectness of this conclusion, but he has undoubtedly made a good deal of progress in that direction. Of the various automatic blocks which have now been experimented with or brought into practice, the Hall Electric and the Union Safety Signal Company systems have been developed to a very marked degree of perfection. They depend for their working on diametrically opposite principles: the Hall signals being worked by means of an electric circuit caused by the action of wheels moving on the rails, and conveyed through the usual medium of wires; while, under the other system, the wires being wholly dispensed with, a continuous electric circuit is kept up by means of the rails, which are connected for the purpose, and the signals are then acted upon through the breaking of this normal circuit by the movement of locomotives and cars. So far as the signals are concerned, there is no essential difference between the two systems, except that Hall supplies the necessary motive force by the direct action of electricity, while in the other case dependence is placed upon suspended weights. Of the two the Hall system is the oldest and most thoroughly elaborated, having been compelled to pass through that long and useful tentative process common to all inventions, during which they are regarded as of doubtful utility and are gradually developed through a succession of partial failures. So far as Hall's system is concerned this period may now fairly be regarded as over, for it is in established use on a number of the more crowded roads of the North, and especially of New England, while the imperfections necessarily incident to the development of an appliance at once so delicate and so complicated, have for certain purposes been clearly overcome. Its signal arrangements, for instance, to protect draw-bridges, stations and grade-crossings are wholly distinct from its block system, through which it provides against dangers from collision and broken tracks. So far as draw-bridges are concerned, the protection it affords is perfect. Not only is its interlocking apparatus so designed that the opening of the draw blocks all approach to it, but the signals are also reciprocal; and if through carelessness or automatic derangement any train passes the block, the draw-tender is notified at once of the fact in ample time to stop it.