48 



THE BOOK OP THE LANTERN. 



Low PRESSURE CYLINDERS CHARGED TO 10 ATMOSPHERES. 



Each cylinder is fitted with a tap to regulate the flow 

 of gas, which tap has a nipple over which the rubber 

 tubing can readily be drawn. The 

 advantage of using a bottle instead of 

 a bag in the one point of bulk is re- 

 markable, as may be seen by the above 

 table. Thus, six cubic feet, which will 

 be sufficient for an hour and a half's 

 entertainment, is contained in a re- 

 ceptacle about the size of a champagne 

 bottle, and which can be placed in 

 the empty lantern-box during use. 

 The amount of gas in a bottle can be 

 readily ascertained by the use of a 

 proper pressure gauge. In fig. 20 one 

 of these cylinders is shown with the 

 regulator and pressure gauge attached. 

 The latter is of the form commonly 

 used on steam engines, and is known 

 as Bourdon's pressure gauge. It depends for its efficiency 

 on the action of internal pressure upon a curved tube of 

 oval section. The greater the pressure the straighter the 

 tube becomes, and this movement is communicated by 

 simple gearing to the index-finger. The following table 

 will be found useful to those who employ compressed gas : 



Fig. 20. 



