THE BOOK OF THE LANTERN. 63 



frames together are of wrought iron and of very solid 

 construction ; for they have to bear some amount of strain. 

 It will be noticed that the sail-cloth is made in two pieces, 

 with eyelet holes along the edges where they meet, so that 

 by means of strong cord they can be laced up and rendered 

 as tight as a drumhead. 



Between the two frames there is secured a sheet of sail- 

 cloth, which is nailed down to the lower board at the 

 hinged end. In the centre of its other extremity is sewn 

 a flattened ring of galvanised iron. Where the sail-cloth 

 is nailed to the woodwork zinc roofing nails should be 

 used, for they will never rust. To the end of the 

 lower frame which is farthest away from the hinges 

 is nailed a strong leather strap, about six feet long, and 

 when the bags are in position this strap is passed through 

 the flattened ring on the midway sheet of sail-cloth, and 

 then through a corresponding opening on the upper frame, 

 where it is secured with a buckle. By means of this strap 

 the two bags are kept in place, while the sail-cloth sheet 

 between them also helps to prevent them slipping back- 

 wards. 



It is customary to place the hydrogen bag below and the 

 oxygen one above, but I am not aware that there is any 

 advantage in so doing. Certainly I have met with operators 

 who prefer to reverse their positions, and seemingly without 

 any disadvantage. 



The taps on the bags should have a large bore, and the 

 tubes which serve to connect them with the lantern should 

 also be of good size. The amount of weight on the 

 bags is governed to some extent by the size of disc re- 



