THE BOOK OF THE LANTERN. 55 



worked outside the lantern, so that it was turned and raised 

 by the same action. But, strange to say, the screw was of 

 so fine a pitch, as in fig. 22, that by one revolution the 

 pitted part of the lime was once more brought under the 

 influence of the jet. In Mr. Wright's arrangement, which 

 I have long ago adopted, the screw is a spiral, which 

 during one revolution raises the lime quite a quarter of an 

 inch. This plan has still further been improved upon by 

 the addition of a nicked wheel, which prevents the lime 

 being turned by the operator more than is necessary for 

 the time being. This addition is known as " Newton's 

 Improved Check-action Lime-movement." The same firm 

 of opticians have carried out a still further improve- 

 ment devised by Mr. Andrew Pringle. This consists 

 of what is called a " cut off," and is applicable only to 

 the mixed gas jet. It gives the operator the means of 

 setting his jet so that the gases are giving the best pos- 

 sible light, and then by the turn of an extra tap cutting 

 them off, with the exception of a small supply of the 

 hydrogen which keeps burning. He can, therefore, adjust 

 his lights beforehand, and feel confident that a turn of 

 the tap will once more render them at their best at a 

 moment's notice. 



There is certainly room for improvement in the manner 

 in which lime jets generally are supported in the lantern. 

 A metal tray, sliding in grooves, forms a base board, at the 

 end of which is an upright rod of iron which, during use, 

 projects at the back of the lantern. Upon this vertical 

 rod the whole jet can be moved up or down, and can be 

 clamped in position by means of a couple of screws, witli 



