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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