164- Things not generally Known. 



occasionally emitted sounds as if they were tapped with a knife, 

 or raised a little and then let fall on the shelf. These sounds 

 preceded wind ; and when they occurred, boats and vessels were 

 immediately secured. The strength of the sound is said to be 

 proportioned to the tempest that follows. 



REVOLVING STORMS. 



By the conjoint labours of Mr. Redfield, Colonel Reid, and 

 Mr. Piddington, on the origin and nature of hurricanes, ty- 

 phoons, or revolving storms, the following important results 

 have been obtained. Their existence in moderate latitudes on 

 both sides the equator ; their absence in the immediate neigh- 

 bourhood of the equatorial regions; and the fcict, that while 

 in the northern latitudes these storms revolve in a direction 

 contrary to the hands of a watch the face of which is placed 

 upwards, in the southern latitudes they rotate in the opposite 

 direction, are shown to be so many additions to the long chain 

 of evidence by which the rotation of the earth as a physical 

 fact is demonstrated. 



IMPETUS OF A STORM. 



Captain Sir S. Brown estimates, from experiments made by 

 him at the extremity of the Brighton-Chain Pier in a heavy 

 south-west gale, that the waves impinge on a cylindrical sur- 

 face one foot high and one foot in diameter with a force equal 

 to eighty pounds, to which must be added that of the wind, 

 which in a violent storm exerts a pressure of forty pounds. He 

 computed the collective impetus of the waves on the lower part 

 of a lighthouse proposed to be built on the Wolf Rock (exposed 

 to the most violent storms of the Atlantic), of the surf on the 

 upper part, and of the wind on the whole, to be equal to 100 

 tons. 



HOW TO MAKE A STORM-GLASS. 



This instrument consists of a glass tube, sealed at one end, 

 and furnished with a brass cap at the other end, through which 

 the air is admitted by a very small aperture. Nearly fill the 

 tube with the following solution : camphor, 2| drams; nitrate 

 of potash, 38 grains ; muriate of ammonia, 38 grains ; water, 9 

 drams ; rectified spirit, 9 drams. Dissolve with heat. At the 

 ordinary temperature of the atmosphere, plumose crystals are 

 formed. On the approach of stormy weather, these crystals ap- 

 pear compressed into a compact mass at the bottom of the tube ; 

 while during fine weather they assume their plumose character, 

 and extend a considerable way up the glass. These results de- 

 pend upon the condition of the air, but they are not considered 

 to afford any reliable indication of approaching weather. 



