Caoutchouc and its Applications. 69 



substance, and the result of this contraction is to reduce the 

 caoutchouc thus acted upon ta its original temperature. 



Among the latest applications of the elastic force of caout- 

 chouc — the chief purport of Mr Brockedon's lecture — atten- 

 tion was directed : 



1. To Mr E. Smith's patent application of tubes of vulcan- 

 ized caoutchouc as torsion springs to roller blinds, — adjusted 

 to the heaviest external blinds of houses, or the most delicate 

 carriage blinds ; and equally applicable to clocks and various 

 machines as a motive power. 



2. To the raising of weights (Mr Hodges' patent applica- 

 tion). — Short lengths of caoutchouc (termed by him Vulcan- 

 ized power-purchases) are successively drawn down from or 

 lifted to a fixed bearing, and attached to any weight which it 

 is required to raise ; when a sufficient number of these power- 

 purchases are fixed to the weight, their combined elastic force 

 lifts it from the ground. Thus ten purchases of the elastic 

 strength each of 50 lb. raise 500 lb. Each purchase is six 

 inches long and contains about IJ oz. of vulcanized caout- 

 chouc. These ten purchases, if stretched to their limit of 

 elasticity, not of their cohesive strength, will lift 650 lb. 

 This power — the accumulation of elastic force — though it 

 obey the common law of mechanical powers, differs enough 

 to be distinguished as a new mechanical power. 



The same principle is applicable to relieve boats in tow 

 from the strain they are subject to, and to easing the strain 

 on ship's cables, especially where several boats are towing 

 one vessel. 



3. Applied as ^ projectile force. A number of power-pui> 

 chases, attached to the barrel of a gun constructed to project 

 harpoons, will exert a power if suddenly relieved proportioned 

 to their aggregate forces. 



Similar contrivances have been made for projecting balls 

 200 yards or more : a charge of No. 4 shot can be thrown 

 120 yards. On the same principle a bow was contrived in 

 which (reversing the usual form) the string alone was elastic ; 

 this bow throws a 30-inch arrow 170 yards. 



There were also exhibited adaptations of this material, for 

 restraining furious horses, — for slinging horses whose limbs 



