Mr. Killingworth Hedges exhibits also a third form of his lamp, in most respects similar to the lamp figured in Fig. 1, but in which the ends of the two carbons rest against the side of a small cylinder of fireclay or other refractory material, which is mounted on a horizontal axis and can be rotated thereon by a worm and worm-wheel actuated by an endless cord passing over a grooved pulley. In the lamp one of the carbon-holders is rigidly fixed to the framing of the apparatus, and the other is mounted on a point so as to enable the length of the arc playing over the clay cylinder to be regulated by the action of an electro-magnet attracting an armature in opposition to the tension of an adjustable spring. In the same exhibit will be found specimens of Mr. Hedges' two-way switches, which have been designed to reduce the tendency to sparking and consequent destruction which so often accompanies the action of switches of the ordinary form. The essential characteristic of this switch, which we illustrate in elevation in Fig. 3 and in plan in Fig. 4, lies first in the circular form of contact-piece shown in Fig. 4, and next in the fact that the space between the two fixed contact-pieces is filled up with a block composed of compressed asbestos, the surface of which is flush with the upper surfaces of the two contact-pieces. The circular contact-piece attached to the switch lever can be turned round so as to present a fresh surface when that which has been in use shows indications of being worn, and a good firm contact with the fixed contact-pieces is insured by the presence of a spiral spring shown in the upper figure, and which, owing to an error in engraving, appears more like a screw than a spring. In order to prevent bad connection through dust or other impurities collecting within the joint, the electrical connection between the fulcrum of the switch lever and the circular contact-piece is made through the bent spring shown edgeways in Fig. 3.--_Engineering._ * * * * * RAILWAY APPARATUS AT THE PARIS ELECTRICAL EXHIBITION. [Illustration: Fig. 1.--Lartigue's Switch Controller Fig. 2--Transverse Section Fig. 3--Longitudinal Section Fig. 4.--Position of the Commutators during the Manuever Fig. 5.--Pedal for Sending Warning to Railway Crossing--Elevation. Fig. 7.--End View. Fig. 8.--Electric Alarm. Fig. 12.--Guggemos's Correspondence Apparatus--External View. Fig. 13.--Interior of the Same. Fig. 14.--Annunciator Apparatus. Fig. 15.--Controller for Water Tanks (Lartigue System). RAILWAY APPARATUS AT THE PARIS ELECTRICAL EXHIBITION.] [Illustration: Fig. 6.--Pedal for Sending Warning to Railway Crossing--Plan View. Fig. 9.--Lartigue's Bellows Pedal--Longitundinal Section Fig. 10.--General Plan. Fig. 16.--Controller for Water Tanks (Verite System). RAILWAY APPARATUS AT THE PARIS ELECTRICAL EXHIBITION.]