APPLICATIONS OF THE ELECTRIC LIGHT. 269 



it is only when the current is made to pass through the right 

 electro-magnet that the latter causes the lever to turn, and 

 pushes the tooth by one notch. The screw rod of the regu- 

 lator then turns, by an amount proportionate to the escape- 

 ment of this tooth, and lowers the corresponding, carbon- 

 holder. If now the lower straight electro-magnet be excited, 

 the tooth of the lever engages the lower ratchet-wheel of the 

 rod, and when the current is' sent through the left electro- 

 magnet the rod in question turns by the space of a tooth of 

 the ratchet-wheel, but in the direction opposite to the former 

 movement; and this causes the carbon to be raised that 

 before was lowered. As the other carbon is capable of 

 being similarly acted upon in the same way, the luminous 

 point can thus be placed at any desired elevation, at what- 

 ever distance the operator may be from the regulator ; and 

 he can separately or simultaneously move both carbons as 

 occasion requires. 



As to the signals, there are two methods of proceeding. 

 Either the light of the signalling apparatus maybe extinguished 

 by a commutator, or the lights may be hid by a screen elec- 

 trically made to descend in front of the arcs. In the latter case 

 the apparatus are fitted up with a special system of electro- 

 magnets, by which the movement is easily effected. De Mer- 

 sanne has fitted up several patterns, which may be applied to 

 any other kind of regulator; the problem is not one of any 

 difficulty. 



The signalling apparatus just described has been made to 

 work by hand ; but the regulation of the light may obviously 

 be automatically produced in a very simple way, by causing 

 a mechanism connected with the light-producing current to 

 act on the commutator already mentioned. 



One small detail in the construction of the commutator is 

 of some importance. It is a platinum wire which glows when 

 the lamp itself is lighted, and is extinguished with the latter. 

 The person sending the signals is therefore aware, although- 

 he may not see the lamp, when this latter is lighted. 



