216 ANNUAL OF SCIENTIFIC DISCOVERY. 



Mr. Vaughan proposed to use the tide-water in the Bay of Fundy as the 

 movable mountain. 



Prof. Henry said this had already been suggested, and added that this 

 delicate problem of the density of the earth was under investigation by the 

 Smithsonian Institution. 



NEW APPARATUS FOR TAKING SPECIFIC GRAVITY. 



Messrs. Eckfeldt and Dubois, of the Philadelphia mint, have described the 

 following new method of obtaining specific gravities: The apparatus for 

 taking the specific gravity of solids, is essentially a tin cup with a spout at the 

 side. Five vessels are here shown, of different sizes and shapes, to suit 

 different cases. Four of these are cylindrical, ranging from six to ten niches 

 high, and from two to five inches in diameter. The tall one (ten niches by 

 two) is intended for the trial of silver spoons and forks, or articles of similar 

 shape ; the others are adapted to lumps of stone or metal, or blocks of wood, 

 of various sizes. The fifth vessel is rectangular, measuring 6|- inches high, If 

 inches long, and inch broad, being intended for corns, not smaller than the 

 half eagle or quarter dollar, and for small medals and gems of admissible size. 

 This vessel is provided with a brass plate, as a plunger, for diminishing the 

 surface. The smaller vessels are set firmly in mahogany blocks, to insure 

 steadiness in the operation ; and these blocks have screw feet, for convenience 

 of levelling. The spouts extend upward, with a curve outward, the beak 

 being far enough below the top of the cup to allow for the space to be taken 

 up by the specimen, that it may not force the water over the top, nor leave 

 any point uncovered by water. The aperture of the spout is tapered to the 

 one-sixteenth of an inch, and a small bit of wire projects downwards from the 

 beak, to carry the drops of water properly. A small cup is placed directly 

 under, to catch the water displaced, and a brass weight, equal to the weight 

 of this cup when empty, is found convenient (though not necessary) as a 

 counter- weight. 



"When the operation is to be performed, suppose upon a gold or silver ore, 

 the ore is first weighed, and afterwards its surface is moistened. The ves'sel 

 is then nearly filled with water, and so much as is superfluous, or above the 

 level of the beak of the spout, runs or drips off, to a final drop. The small 

 cup is then set under the beak, and the lump is carefully lowered into the 

 vessel by a hair wire or waxed thread. t This, of course, displaces its own 

 bulk of water, which runs off into the small cup, gradually coming back to 

 the former level, by a final drop. The weight of this water is the divisor, the 

 weight of the lump the dividend, and the quotient is the specific gravity. 



ACTION OF WAVES ON SEA BEACHES. 



An attentive examination of the accumulative and destructive action of the 

 waves upon shingle beaches has produced a rule, so far as one can be formed 

 upon this subject. It has been observed that when seven, or any less num- 

 ber of waves fall upon the shore per minute, that then a destructive action is 

 going on or, in other words, that the shingle is disappearing. But that 

 when nine or any greater number of waves beat upon the shore in the same 



