NATURAL PHILOSOPHY. 129 



as a stream, from a like cause with that of the Gulf Stream, namely, 

 its lightness, lifted above the sea level by the bottom pressure and 

 inflow of the heavy sea water in the opposite direction. 



The striking variations in the velocities of the Gulf Stream, 

 which were particularly remarked by navigators during the late 

 survey, the weather being exceedingly calm, are accounted for 

 on the hypothesis that they follow the changes in mean sea level 

 which depend upon the declinations of the sun and moon, more 

 especially the latter. Prof. Bache has shown that the mean level 

 at Key West is one foot higher when the moon is on the equator 

 than when she is at her greatest declination ; while, on the con- 

 trary, in the North Atlantic the mean level is about 3 inches 

 higher at her maximum declination ; giving a variation of 15 inches 

 in level to account for the variations in the velocity of the stream. 

 Scientific American. 



MOUNTA'IN ATTRACTION. 



The pendulum experiments carried on in India in connection 

 with the Trigonometrical Survey show that, contrary to theory, 

 the nearer the observing stations are to the Himalayas the less is 

 the force of gravity, the difference between theory and fact dimin- 

 ishing with the increase of distance from the hills. This seems to 

 confirm the opinion of Prof. Airey that the strata of the earth be- 

 low the mountains are less dense than the strata below plains and 

 the bed of the sea. 



FLUID RESISTANCE. 



Until recently the main expenditure of power in screw vessels 

 was supposed to be occasioned by the necessity of separating the 

 water at the bow and closing it at the stern. In 1855 Mr. John 

 Bourne promulgated the doctrine, that in ordinary well-formed 

 vessels only a small part of the power expended is consumed for 

 this purpose, the principal resistance being due to the friction of 

 the water on the bottom of the ship. 



LEAD FLOATING ON MOLTEN IRON. 



Some experiments have been made in Germany which seem to 

 show that molten lead when dropped upon liquid iron remains 

 floating on the surface of the latter. As the specific gravity of 

 lead (11.5) is more than one-half greater than that of cast iron 

 (7), there arose some discussion on this subject, which has been 

 recently closed in a very satisfactory manner by the researches of 

 Prof. Karmarsch, of Hanover. An ironmaster in the vicinity of that 

 town had sent to the professor some samples of such drops of lead 

 lying imbedded in the surface of a cast-iron block, and which had 

 been produced in the manner above described. Prof. "Karmarsch 

 found, upon close examination, that these drops of lead, instead 

 of being solid globules, as was supposed at first sight, were all 

 hollow, forming bubbles composed of a metallic skin, and appar- 

 ently empty in the centre, so far as his observation has been car- 



