166 Account of Experiments made 
Experiments on different Metals. 
Ibs. avoirdupoise. 
; Xi cast copper, crumbled with .. ae <- eee 
;X4 fine yellow hrass reduced =, with 3213: } with 10304 
1x wrought.copper;. .. as 3427: = 6446 
2X cast tin, oa cel Ae 502° + 966 
if SUeast lead; °*". : . a's eee 483* 
The anomaly between the three first experiments on + cubes, 
and the two second of a different length, can only be accounted 
for, on the difficulty of reducing such small specimens to an 
equality. The experiments on ¢ inch prisms of different lengths 
give no ratio. The experiments on } inch cubes, taking an 
average of the three first in each, give a proportion between them - 
and the three on ¢ cubes, 
as | : 6-096 in the block castings 
as 1 : 7°352 in the horizontal ditto 
as ] : 8-035 in the vertical ditto 
in several cases the proportion is as the cubes. 
The vertical cube castings are stronger than the horizontal 
cube castings. 
The prisms usually assumed a curve similar to a curve of the 
third order, previous to breaking. 
The experiments on the different metals give no satisfactory 
such as the position of the specimen, the form of its surfaces, and the in- 
equality of the different specimens—which were so extremely small that 
it would be scarcely possible to obtain any tolerable devree of accuracy. 
Gauthey’s experiments exhibit a like irregularity, indicating no relation 
between the height of the piece and its resistance (Rozier’s Journal, tome iv. 
p-407.) It appears probable that when the fracture is of that kind where 
the body decomposes into pyramids, the length does not influence the re- 
sult, provided that the piece be long enough to admit of the free motion 
of the fractured parts. Iimagine that hard cast-irou breaks into pyramids, 
but the nature of the fracture Mr. Rennie has not stated. Probably it was 
so soft as to break in the manner of flexible bodies, in which, though the 
forces must act according to some regular law, it is difficult to trace their 
operation in a continuous solid.—T. T. 
* The degree of compression of these bodies having been observed, we 
might conclude that the height ef the modulus of elasticity might be ob- 
tained from these experiments. This however is not the case; and so far 
proves that the strain is not of that simple kind which it has been supposed 
to be. The reduction of length might be easily measured, even in hard 
bodies, by an apparatus for multiplying its extent; and it would throw 
mitch light on the subject, toreduce pieces of the same length, but of dif- 
ferent areas, toa given length. Such a set of experiments would be in- 
finitely nore valuable than those on the fracture, and much more easily 
made, as the apparatus would be easicr to manage. 
The inportance of the laws of stiffness over those of strength has heen 
ably stated by Dr. Young, (Lectures on Natural Philosophy, vol.i.) and what 
he has stated in favour of stiffness applies equally to the mode of experi- 
menting [ now recommend, which could not fail of establishing some im- 
portant practical rules.—Y. T. 
results. 
