AMERICAN INSTITUTE. 463 



torn; tlie cars acquired certain velocities in descent. First, a load of 1,120 

 pounds was placed at rest on a pair of iron bars nine feet long, four inches 

 wide, and one and one-half inches deep, occasionaing a deflection of six- 

 tenths of an inch. It was then passed over by the car at the rate of ten 

 miles per hour, whereby the deflection was increased to eight-tenths. 

 Finally, at thirty miles per hour, when the deflection was one and a half 

 inches. It follows that a much less load will break the bars in passing over 

 them than when it is placed on the bars in a state of rest. 



In the above example, a weight of 4,150 pounds is required to break 

 the bars when placed on the centers ; but a weight of 1,778 pounds is 

 sufficient to produce fracture at the velocity of thirty miles an hour. The 

 bars, when broken, were always broken at points beyond their centers, and 

 often into four or five pieces, thus indicating the great and unusual strain 

 they had been subjected to. 



The Britannic Tubular Bridge was tried by a train of twenty-eight wagons 

 and two locomotives, with 280 tons of coal, was drawn into all four tubes 

 and caused a deflection of only three-fourths of an inch. They were then 

 sent through after a start of a mile at the greatest velocity, and the deflec- 

 tion was less ! 



VALUE OF DIAMONDS. 

 I was informed by a jeweller the other day that diamonds are weighed 

 and valued by the carat, containing four grains. Tennant read a paper 

 recently before the London Society of Arts, in which he says a diamond 



containing one carat is worth $40 00 



Eight carats, 1,000 00 



Ten carats, 1,500 00 



Thirty carats, 36,000 00 



Fifty carats, 100,000 00 



One hundred carats, 400,000 00 



The diamond may be known from other precious stones from the fact 

 that it has only single refraction, whereas all others have double, except 

 the garnet ; that is to say, they give a two-fold image of a taper or minute 

 light when looking through their facets. 



My test, which I suppose is known to every one, to discover artificial 

 from real diamonds, is to immerse them in strong alcohol, when not only 

 artificial diamonds but all real and artificial stones will lose their lustre, 

 except the true diamond alone. 



The diamond, when applied to glass, does not cut it as is supposed, but 

 merely forces the particles of glass apart without destroying them, the 

 same as a wedge forces wood. It is not necessary that the diamond should 

 penetrate the glass even to the three hundredth part of an inch to produce 

 the required eifect. As i\ passes over the glass, the crack confines itself 

 to a mathematical point at the bottom of the line, and little or no effect Ls 

 afterwards required to produce the desired result. 



