172 Account of Experiments made 
Remarks. 
In observing the results presented by the preceding table, it will 
be seen that little dependence can he placed on the specific gra- 
vities of stones, so far as regards their repulsive powers, although 
the increase is certainly in favour of their specific gravities. But 
there would appear to be some undefined Jaw in the connexion 
of bodies, with which the specific gravity has little to do. Thus, 
statuary marble has a specific gravity above Aberdeen granite, 
yet a repulsive power not much above half the latter. Again, 
hardness is not altogether a characteristic of strength, inasmuch 
as the limestones, which yield readily to the scratch, have never- 
theless a repulsive power approaching to granite itself *. 
It is a curious fact in the rupture of amorphous stones, that 
pyramids are formed, having for their base the upper side of the 
cube next the lever, the action of which displaces the sides of 
the cubes, precisely as if a wedge had operated between them. 
I have preserved a number of the specimens, the sides of which, 
if continued, might cut the cubes in the direction of their dia- 
gonals. 
Experiments made on ihe transverse Strain of cast Bars, the 
Ends loose. June 8th, 1817+. ° 
Weight of the dist. of bearings. Ibs. 
bars, lbs. oz. tt. avoir. 
135 Bar of | inch square He) to AO dG 3 0 897 
136 f Do. of 1 inch do. airs 9 8 DENS: 1086 
137 | Half the above bar Ae Sng 1 4 2320 
138 Bar 
* A curious circumstance was observed by Rondelet in his experiments ; 
viz. that the blocks from the middle of a stratum of stone were of a higher 
specific gravity than those taken either from the upper or lower part of the 
stratum. The stones were from Chatillon, Bagneux, &c. Le also observed, 
that in the same kind of stoue the strength was as the cube of the specifie 
gravity. (L’ Art de Batir, tome iii. p. 83, et suiv.) That any relation should 
exist between the specific gravity and strength of stones of different kinds 
was not to be expected, as the streneth depends on other properties.—T.T. 
+ It is in these experiments that we have most to regret the want of obser- 
vations, and those of'a vature that would haveadded little to the labour which 
all who make such experiments must undergo. It is however a labour that 
is to a mind enyaved in the search of knowledge, more pleasing than those 
unaccustomed to such feelings can conceive. But too often it is a pleasure 
that cannot be pursued, except at an expense and encroachment on the 
hours of business which a professional man. can ill afford to indulge in. 
The defect of these experiments copsists in the want of observations on the 
flexure produced by given weights, particularly in the first degrees of de- 
flexion; and itis the more to be regretted, because we have very few ex- 
periments on cast-iron where such observations have been made. Banks 
states that his specimens bent about an inch at the time of fracture; and 
Dr. Young has calculated the height of the modulus of elasticity from this 
statement, (Nat. Phil. vol. ii. art. $26); but it is weil known that the de- 
flexion is not regular when the piece is nearly broken, In Banks's experi- 
ments 
