THE BOOK OF THE LANTERN. 57 



ence. A simpler plan is that recently introduced by Mr. 

 Steward, and shown at fig. 24. In this case a tongue of 

 metal is fixed to the supply pipes of the jet, and this 

 tongue has a slot in its centre, which engages a vertical 

 pin on the lantern tray. This pin is threaded so that a 

 couple of discs can firmly clamp the metal tongue when 

 the jet has been once centered. Once clamped in this 

 way, the jet cannot be moved until it is released by 

 unscrewing the discs. 



Another valuable improvement is represented by Wood's 

 lime cylinder shield, which is shown, fitted to a jet, at 

 fig. 25. It consists of a metal cylinder, rather larger than 



FIG. 25. 



the lime, in which the latter is free to turn. There 

 is an opening in front, through which the incandescent 

 lime can throw its light towards the condensing lens. 

 In jets, generally, the lime is quite exposed, and unless it 

 be gradually heated will often crack to pieces, by the 



