46 OPTICAL PROJECTION 



make a tight fit with the tubing ; but if there is any doubt 

 about this, small strong vulcanised rings (of which the Ian - 

 ternist should always have some in his box) will make all 

 secure. It is a better plan, however, for a travelling operator 

 to carry some yards of cornpo gas-pipe for bringing up distant 

 supplies of gas. 



26. The Oxy-Spirit Jet. All forms of the lime-light in 

 which oxygen alone is used under pressure, are generally called 

 the * oxy-calcium ' light. Of this there are two main forms. 

 The first is where a fine jet of oxygen is blown through the 

 flame of some volatile fluid, usually methylated spirit. This 

 form of the lime-light was invented by Lieut. Drurnmond in 

 1826, and was formerly largely used, but is now chiefly em- 

 ployed in country 

 villages where gas 

 is still unprocur- 

 able. The present 

 usual form of this 

 jet is shown in fig. 

 28, where a cistern 

 A B outside the lan- 

 tern, adjustable on 

 a rod by a clamp - 



FIG. 28. Spirit Jet J 



screw P, feeds the 



alcohol to a small circular wick, through the flame of which, 

 almost non-luminous in itself, the oxygen is blown by a nipple 

 c, pierced with a very small bore, on to a cylinder of lime D, 

 which can be rotated on a spindle E, and adjusted at different 

 distances from the flame. G is the stopcock to control the 

 oxygen from o. A very good light, equal to a disc of twelve 

 to fifteen feet in diameter, can be obtained in this way, pro- 

 vided the jet be adjusted as described (see 28) a little farther 

 on. If the cistern is arranged, as it generally is, outside, 

 where it cannot be dangerously heated, no possible accident 

 can occur with this jet except by upsetting the fluid. All the 



