1 64 ELECTRIC LIGHTING. 



plane, and the other, by means of an eccentric, displaces the 

 carbon in the vertical plane perpendicular to the former. 



Serrin has made several patterns of his regulator to suit 

 the greater or less electric intensities that are to act upon it. 

 His largest pattern is arranged to burn carbons of 15 milli- 

 metres broad, or 225 square millimetres in section; and, in 

 spite of these large dimensions, it is as sensitive as the smallest 

 patterns. In the pattern made for lighthouses, the inventor 

 has made several important modifications. Thus, by means 

 of a little arrangement adapted to the chains of the carbon- 

 holders, he has been able to shift the luminous point to a 

 certain extent without putting out the light. This is very 

 important in the application of these apparatus to lighthouses, 

 for it gives the means of correctly centring the light with 

 regard to the lenses. 



Again, as these regulators have to act with extremely 

 powerful currents, the heat in the circuit would be sufficient 

 to burn the .insulating covering of the coil in the electro- 

 magnet, and thus destroy its effect. Serrin has made the 

 electro-magnetic spirals with metallic helices unprovided with 

 insulating covering, and so arranged that the spires cannot 

 touch each other. In order that these helices might be 

 adapted to the magnetic cores and to the discs of the electro- 

 magnet with a sufficient insulation, he has covered these cores 

 with a somewhat thick layer of vitreous enamel, as well as the 

 inner parts of the discs ; and in order to obtain as many spires 

 as possible with the maximum of section, he has cut these 

 helices from a copper cylinder of a thickness equal to that 

 of the coils. In this way the electro-magnetic helices are 

 represented by a kind of close screw thread of a projection, 

 equal to that of the discs, and having its central part repre- 

 sented by the magnetic cores and the covering of enamel. 



It will easily be understood that with this arrangement the 

 helices may be carried to a very high temperature without 

 the spires ceasing to be insulated from each other, for they are 

 not in contact, and they are separated from the body of the 



