PONTON RAFTS. 139 



AIR BALSOR. 



Fig. , plate , represents a balsor or single air cylinder, 

 one of the earliest manufactures of the Roxbury Company. 

 They were made of India rubber canvas, and inflated by a 

 hand bellows. They were designed to be used as a life-spar or 

 buoy, or to be fastened to boats to keep them from swamping. 

 These, as well as the other articles in which air alone is relied 

 upon for their buoyancy and safety, are unsafe and not to be 

 depended upon compared with the self-inflating pontons and 

 boats specified in Chapter XXX. They are here noticed be- 

 cause they were the first of this kind of work, and because they 

 are the cheapest made, and would answer a good purpose in the 

 absence of better things. 



AIR PONTON RAFTS. 



These may be constructed either of the air balsors or wagon 

 float cylinders. For this purpose they are connected together 

 in the same way as the self-inflating ponton rafts, more particu- 

 larly specified. Chapter XXX. They are more cheaply made, 

 but not so convenient or safe as the self-inflating ponton rafts. 

 See plate , fig. . 



