POPULAR MISCELLANY. 



141 



search for this peculiar alluvial deposit, 

 which is generally free from any admixture 

 of clayey earth, the digger has often to pen- 

 etrate into the jungle that grows thickly 

 around, and combines the work of clearing 

 with the occupation of gem-digger. No sap- 

 phire has yet been extracted of higher value 

 than about fourteen hundred dollars, or ruby 

 of higher price than forty-eight hundred dol- 

 lars. No artificial or mechanical processes 

 for washing the soil have so far been intro- 

 duced. Rubies and sapphires are found at 

 all the diggings, often deposited side by side, 

 in the same layer or stratum of sand. The 

 rubies are usually of a dull, light-red hue. 

 The sapphire is of a dark, dull blue, without 

 any of the silken gloss distinctive of the 

 Burmah and Ceylon stones. Stones resem- 

 bling garnets rather than rubies are found in 

 the dried beds of water-courses at Raheng, 

 two hundred miles north of Bangkok, and 

 there is every reason to believe that rubies, 

 also, at least equal to those discovered in 

 the southeast, exist throughout the Raheng 

 district. 



What may be learned from a Spinning 

 Top. The earth as a spinning top was sub- 

 stantially the subject of an " Operatives' 

 Lecture," by Prof. John Perry, at the British 

 Association. The lecturer's purpose was to 

 exhibit the analogies between the motions of 

 tops and the rotation of the earth, and show 

 how many phenomena can be explained by 

 them. He said that, if more attention was 

 paid to the spinning of tops, much greater 

 advances would be made in mechanical en- 

 gineering and industrial invention ; geolo- 

 gists would not make so many mistakes of 

 millions of years in their calculations ; and we 

 should all have a much better knowledge of 

 astronomy, of light, of magnetism, and of 

 electro-magnetic subjects. First the lect- 

 urer illustrated the 9*<cm'-rigidity that rapid 

 rotation gives to a flexible or fluid body. A 

 thin sheet of paper assumed the stiffness of 

 a board. A chain released from a hub rolled 

 like a solid wheel. A fly-wheel being made 

 to revolve rapidly when inclosed in a brass 

 box, the box did not tumble down, but main- 

 tained a vertical position and offered resist- 

 ance to any attempt- to turn it round. If it 

 was tilted, it turned with a precessional mo- 

 tion. Every spinning body, the lecturer 



said, resists a change of direction of its spin- 

 ning axis. Rotating machines on board 

 ship offer greater resistance to pitching and 

 rolling. A top thrown up would fall down 

 anyhow ; but if it was thrown up spinning, 

 there would be no doubt as to the position it 

 would come down in, because the spinning 

 axis always keeps parallel with itself. The 

 fall of a biscuit or a hat is equally controlled 

 by throwing either with a spinning motion. 

 For this reason the barrels of guns are rifled ; 

 and the same principle explains the feats of 

 jugglers with hats, hoops, plates, umbrellas, 

 and knives. All that appears incompre- 

 hensible in the curious motions of the gyro- 

 stat under various conditions loses its mys- 

 tery when the motions are regarded as rota- 

 tion about various axes ; and herein is found 

 the key to the phenomenon of precession. 

 The application of these principles to the 

 motion of the earth was illustrated by dia- 

 grams and by the wabbling motion communi- 

 cated by the hand to objects with three axes, 

 which, spun first on the shortest axis, would 

 of themselves rise to spin on the longest 

 axis. A circular chain hanging vertically 

 from a cord, when made to revolve rapidly, 

 first wabbled and at last became a horizontal 

 ring. In dealing with the question whether 

 the earth is a shell filled with fluid, the pro- 

 fessor gave a vibratory motion to vessels 

 containing respectively sand, treacle, oil, and 

 water. A boiled egg had a slower oscilla- 

 tion than an unboiled one. When the two 

 eggs were rolled, the unboiled one stopped 

 sooner than the boiled one. The liquid in- 

 side went on moving and renewed the motion 

 of the shell after it had been stopped by the 

 finger. It is easy to spin a boiled egg, but 

 not an unboiled one. 



Sheep-raising in Algeria. Sheep-rais- 

 ing is the principal business of the Algerian 

 Arabs of the high plateaus. Neither the 

 sheep nor the wool are of the first quality, 

 but the sheep can resist a great variety of 

 hardships to which they are subjected in the 

 not very pleasant region they live in. As 

 they require to be watered every two or 

 three days in summer, they can not be taken 

 for pasturage to regions far removed from a 

 supply. They are not at all particular about 

 the quality of what they drink, but water of 

 some kind they must have ; and no use can 



