USEFUL AETS. 



CHAPTER XII. 



The Cassava Press and its Structure. Mode of using it. The Siamese Link. 

 An ingenious Robbery. Muscles and their Mode of Action. Human Arms 

 and Steelyard. Change of Direction. The Human Hand and "Wrist. 

 Story of a Carpenter. The Pulley. Reduction by Friction. Past and 

 present Engines. Oiling Machines. Treatment of the Sewing Machine. 

 Use of Paraffine. Disuse of Machine hurtful. Human Joints. Synovia 

 and its Value. Disuse of Joints hurtful. The Lazy-tongs and its "Useful- 

 ness to Invalids. Suggestions for Improvement. Larva of the Dragon- 

 fly and its Mask. Curious Mode of seizing Prey. Proboscis of the House- 

 fly, and Mode of using it. The Apple-parer. Squirrel and Nut. Structure 

 of Teeth. Rock -splitting. Powers of Ice. How the Pebble-ridge is 

 formed. Splitting Stones by Moisture. The Diamond Drill. Ovipositor of 

 the Gad-fly. Curious Similitude of Structure. 



MEANS AND APPLIANCES. 



IN this chapter we will take some miscellaneous appliances of 

 force both in Art and Nature. 



In the accompanying illustration is shown the Cassava Press 

 of Southern America, a most effective and simple instrument 

 for extracting the juices of the root. These juices are poisonous 

 when raw, but, when properly boiled and cooked, they make an 

 excellent sauce. 



The press in question is an elastic tube made of flat strips of 

 cane woven together exactly like the " Siamese Link," which 

 will be presently described. The cassava root, after having 

 been scraped until it resembles horseradish, is forced into the 

 press until it can hold no more. The result is, that the tube is 

 shortened and thickened, being widest in the middle. 



It is then hung by its upper loop to the horizontal beam of a 

 hut. A long pole is passed through the lower loop, the short 

 end is placed under a projecting peg on the upright post of the 

 house, and a heavy weight attached to the longer end. A 

 powerful leverage is thus obtained, the tube is forcibly short- 



