NATURAL PHILOSOPHY. 175 



anionnt for a known time, according to the qnantit^y the clock is 

 fast or slow. The suspending spring passes through a fine slit in 

 a piece of steel, which is capable of being raised or lowered by a 

 cam to a certain extent. An index in the axis of the cam, moving 

 over a dial, shows the extent to which the loendulum has been 

 shortened or lengthened. Suppose the clock to be thirteen-hun- 

 dredths of a second fiist ; the index is to be turned so as to point 

 to the word losing on the dial, and allowed to remain there for 

 five minutes twelve seconds, in the example given by Mr. Lang, 

 At the end of this time it must be turned back so that the index 

 points to mean rate. By this operation the clock is put back to 

 true time. 



DEPTHS OF THE SEA. 



A French journal says that the soundings for the new trans- 

 Atlantie cable have enabled comparisons to be made of the depths 

 of the difterent seas. Generally speaking, they are not of any 

 great depth in the neighborhood of continents. Thus, the Baltic, 

 between Germany and Sweden, is only 120 feet deep ; and the 

 Adriatic, between Venice and Trieste, 130 feet. The greatest 

 depth of the channel between France and England does not ex- 

 ceed 300 feet, while to the southwest of Ireland, where the sea is 

 open, the depth is more than 2,000 feet. The seas to the south of 

 Europe are much deeper than those in the interior. In the nar- 

 rowest part of the Straits of Gibraltar the dejDthis only 1,000 feet, 

 while a little more to the east it is 3,000 feet. On the coast of 

 Spain the depth is nearly 6,000 feet. At 250 miles south of Nan- 

 tucket (south of Cape Cod), no bottom was found at 7,000 feet. 

 The greatest depths of all are to be met with in the Southern 

 Ocean. To the west of the Cape of Good Hope, 16,000 feet have 

 been measured, and to the west of St. Helena, 27,000. Dr. Young 

 estimates the average depth of the Atlantic at 25,000 feet, and of 

 the Pacific at 20,000. 



FRACTURING CAST-IRON "WITH WATER. 



Advantage has recently been taken of the non-compressibility 

 of water, to effect th"e reduction of large masses of cast-iron in 

 France. The method, which is simple and ingenious, consists in 

 drilling a hole in the mass for about one-thii-d of its thickness, and 

 filling the hole with water ; then closing it with a steel plug which 

 fits very accurately, and letting the ram of a pile-driver fall on 

 the plug. The first blow separates the cast-iron into two pieces. 



AMSDEN'S HYDROSTATIC SCALE, 



The simple principle of this scale, viz., that a floating body 

 sinks in water until it has displaced a quantity of water equal in 

 weight to itself, is as old as Archimedes ; the scale of Mr. Amsdea 

 therefore acts by the displacement of the water, and not by 

 hydraulic pressure. It claims to supply the very important desid- 



