NATURAL PHILOSOPHY. 185 



new Liverpool observatory, after the experience of the j^reat 

 storm of December, 1863, the anemometer sheet was made to 

 register GO lbs., which was supposed to be ample for any gale in 

 that latitude. On February 1, 1868, after two days of a north- 

 westerly storm, the registering pencil went far beyond this limit, 

 and it is estimated up to 70 or 80 lbs. to the square foot, — a pres- 

 sure probably rarely exceeded by the gales of the West Indies. 

 The barometer stood at 29*^ at the time. 



Tides at Hell Gate. — At the last meeting of the National Acad- 

 emy of Sciences, Mr. Henry Mitchell presented a paper on the 

 tides of Hell Gate. It is new, and deeply interesting to New 

 York merchants. It goes to show that the two tides entering l)y 

 Sandy Hook and Hell Gate form there a tide neither the sum nor 

 more than the sum of the two, but of an intermediate depth. If 

 the tides met there at the full it would be different, but one is 4 

 hours behind the other, and 65 per cent, of the whole tide is the 

 result. Looking at the increase of Sandy Hook, it is clear that 

 Hell Gate acts as maid-of-all-work to the harbor and sweeps its 

 floors clean. In fact, the tidal circulation of Hell Gate is the life- 

 blood of the harbor and saves it from destruction. 

 16* 



