190 Miscellanies. 



13. Pressure of Sand. — From a letter by M. Huber Burnaud to 

 Professor Prevost, on this subject, the following conclusions may be 

 drawn. In a given time, the quantity of sand which flows is con- 

 stant, whatever be the height of the column and the pressure which it 

 is made to undergo. Sand flows through a fissure from two to three 

 millimetres in diameter, in the direct ratio of the length of the fissure. 

 A greater diameter induces an increase in the flow which surpasses 

 the simple proportion of the surface of the orifice. Some grains of 

 sand isolated upon an inclined plane, flow only when the inclination 

 has attained thirty degrees. Sand in a heap presents itself, after the 

 flowing off" of its mass, under an angle which varies from thirty to thirty 

 three degrees. If sand be poured into the branch of a syphon which 

 contains mercury, the latter does not change its level in the opposite 

 branch. There must be concluded from this that the weight of the 

 sand is almost entirely supported by the walls of the tube. The 

 author has verified this conclusion by direct experiments. The 

 same phenomenon took place in conical tubes, the mouth of which 

 was turned downwards, provided the inclination of its walls did not 

 exceed thirty degrees. — Bulletin des Sc. Mathematiques. 



14. Cement from Iron Filings. — M. Mailtre having reflected 

 upon the action of vinegar in the preparation of the cement known 

 as mastic le limaille, which is made of iron filings, garlic and vinegar, 

 so proportioned as to form a mass of moderate consistency proposed 

 to substitute for the vinegar sulphuric acid diluted with water, in the 

 propordon of one ounce to a little more than two pints of water, and 

 to reject the garlic as useless. This alteration was soon adopted 

 by all to whom he communicated it in Paris, and will save in Paris 

 alone more than ten thousand francs annually. This cement is there 

 employed to close the seams of the stones with which terraces are 

 covered. The iron filings becoming oxidized, occupy a larger space, 

 their oxidation being facilitated by the action of the acid, and the 

 joints become exactly closed. 



15. Concentration of Sound. — It happened says Dr. Arnott, once 

 on board a ship sailing along the coast of Brazil, far out of sight 

 of land, that the persons walking on deck, when passing a particular 

 spot, always heard very distinctly the sound of bells, varying as in 

 human rejoicings. All on board came to listen, and were convinced j 

 but the phenomenon was most mysterious. Months afterwards it 



