NATURAL PHILOSOPHY. 167 



upper ball being still continued into a similar tube. Above the mer- 

 cury, which rises to the middle of the lower ball, oil of juniper is put 

 until it reaches the middle of the upper ball, and then colored weak 

 spirit is placed above the oil. The length of the column of mercury 

 may be considered as a measure of the total gravitation of the earth, 

 and the variations of this length are rendered very sensible by the 

 differential apparatus, consisting of the two balls, and read off on a 

 scale of about three inches length attached to the tube rising from the 

 upper ball. The instrument hangs in the cabin of the ship. Govern- 

 ment were kind enough to send a vessel with the author and the 

 instrument to the Bay of Biscay to make experiments with it, and its 

 indications of the depth of water under the ship were found to be 

 within less than ten per cent, from the truth as determined by the 

 lead. 



MOVEMENT OF SEA AND LAKE WATER. 



The fact that the movement of sea and lake water is confined to 

 the surface is proved by the circumstance, that while the inclination of 

 sand (where the bottom, near the shore, is composed of that material) 

 may be seven horizontal to one perpendicular within the range of the 

 tides and waves, it often stands at only two to one a short distance 

 below, or at the natural slope of sand in still water. This is the case 

 on the shore of the Lake of Geneva, near Vevay ; and a similar result 

 was observed at Cherbourg, with respect to the small materials thrown 

 into the sea for the formation of the breakwater, and which took a 

 slope, below low water, of one to one. 



THE GYRATORY MOVEMENT OF A LIQUID MASS. 



"We translate the following from the Presse Scientifique des Deux 

 Mondes : 



M. Perrot presented to the French Academy, in the month of Oc- 

 tober, 1859, a note, in which he expressed the opinion that the gyra- 

 tory movement which manifests itself in a liquid mass, while it is 

 running out through a small circular orifice in the horizontal bottom 

 of a cylindrical vase, is an immediate effect of the diurnal movement 

 of the earth. M. Magnus, on the contrary, had attributed the gyra- 

 tory movement to the perturbation occasioned by a material obstacle 

 or an exterior movement in the convergence of the liquid molecules 

 toward a common centre. M. F. Laroque has just reexamined the 

 question, and numerous experiments, made on a zinc cylindrical vase 

 of larger dimensions than those employed by M. Magnus, have led to 

 the following conclusions : 



First. If there exist near the orifice any obstacles which modify the 

 rectilinear convergence of the molecules toward the orifice in diame- 

 tral planes, there may result a gyratory movement which changes 

 sensibly the physical constitution of the liquid vein. But this move- 

 ment propagates itself only to a very short distance from the orifice, 

 and never rises gradually to the surface whenever the liquid is more 

 than about four inches in depth ; nor in any case does it communicate 

 itself to the liquid mass. 



