=Becquerel Ray and Radiation.= An invisible ray discovered by Becquerel, which is given out by some compounds and chemicals--notably uranium--and which has the power to penetrate many opaque bodies and objects impenetrable to the actinic rays of ordinary light. These rays are used chiefly in connection with the photographic dry-plate. =Bell, Electric.= A bell rung by electricity. The current excites an electro-magnet, attracting or releasing an armature which is attached to a vibrating or pivoted arm, on the end of which the knocker is fastened. =Bichromate of Potash.= A strong, yellowish-red chemical, used chiefly in battery fluids and electrolytes. =Bifilar Winding.= The method followed in winding resistance-coils. To prevent them from creating fields of force, the wire is doubled and the looped end started in the coil. Since the current passes in opposite senses in the two lays of the winding, no field of force is produced. =Binding.= Unattached wire wound round armature-coils to hold them in place. =Binding-post.= An arrangement for receiving the loose ends of wires in an electric circuit and securing them, by means of screws, so that perfect contact will be the result. =Bi-polar.= Possessing two poles. =Bi-telephone.= A pair of telephones arranged with a curved connecting arm or spring so that they can be simultaneously applied to both ears. =Blasting, Electric=. The ignition of a blasting charge of powder, dynamite, or other high explosive by an electric spark, or by the heating, to red or white heat, of a thin wire imbedded in the explosive. =Block System.= A system of signalling on railroads. Signal-posts are arranged at stated spaces, and on these signals appear automatically, showing the location of trains to the engineers of trains in the rear. =Bluestone.= A trade name for sulphate of copper in a crystallized state. =Bobbin.= A spool of wood or other non-conducting substance wound with insulated wire. In a tangent galvanometer the bobbin becomes a ring with a channel to receive the wire. =Boiling.= In secondary, or storage, batteries the escaping of hydrogen and oxygen gases, when the battery is fully charged, resembles water boiling. =Bonded Rails.= Rails used in an electric traction system, and which are linked or connected together to form a perfect circuit. Used principally in the third-rail system. =Brake, Electro-magnetic.= A brake to stop the wheels of a moving car. It consists of a shoe, or ring, which by magnetic force is drawn against a rotating wheel to stop its revolution. =Branch.= A conductor which leads off from a main line to distribute current locally. =Brassing.= A process of electro-depositing brass in a bath containing both copper and zinc. A plate of brass is used as an anode. =Brazing, Electric.= A process in which the spelter is melted by electric current, so that the two parts are united as one. =Break.= A point where an electric conductor is broken, as by a switch or a cut-out.