on the Strength of Materials. aL 
June 5th, 6th, and 7th, 1817. 
No. Spec. gray. lbs. avoirdu. 
117 Yorkshire paving with the strata 2°507 12856 
118 Ditto, do. against the strata... 2°507 12856* 
119 White statuary marble not veined 2:760 13632 
120. Bramley Fall sandstone, near mar 2506 13632 
with strata... i Ai 
121 Ditto, against the strata oe 2°506 13632 
122 Cornish granite ; a 2°662 14302 
kinds! ): Be ey 
124 A two-inch cube of Portland .. 2°423 14918 
125 Craig Leith with the strata wt 2°452 15560 
123 Dundee sandstone or brescia, two \ 9-530 14918 
126 Devonshire red marble, variegated Ns 16712 
127 Compact limestone e. Pht 28584 17354 
128 Peterhead granite hard close grained a 18636 
129 Black compact limestone, Limerick = 2°598 19924 
130 Purbeck... os As 2°599 20610 
131 Black Brabant marble .. we 2:697 20742 
132 Very hard freestone ee aa 2°528 21254 
133 White Italian veined marble... 2-726 21783 
134 Aberdeen granite, blue kind a 2°625 245567 
N.B. The specific gravities were taken with a delicate ba- 
lance, made by Creighton of Glasgow, all with the exception of 
two specimens which were by accident omitted f. 
* Gauthey tried the stones in different positions in respect to their na- 
tural beds; but from a general view of his experiments it does not appear 
that he was correct in concluding them to be stronger when “ posées en dé- 
lit,” because his comparison is made between means that include sections 
of very different forms. (Rozier’s Journ. tome iv. p. 406.)—T. 1’. 
+ According to Gauthey’s experiments a cubic inch 
of brick, specific gravity 1°557, was crushed by 1562 Ibs. avoirdupoise. 
of Flanders’ marble - 2°628 - ~ 13142 
of Genvese do. - 2700 - - 4856 
of porphyry - - 2871 - - $5568.—T. T. 
{ Mr. Rennie has of conrse taken the specific gravity in the usual manner, 
but certainly not the real specific gravity of the stone in any of the porous 
ones, though it may be that of the material the stone is composed of. When 
a stone is porous—and many building stones are very much so—it will be 
found that the specific gravity as usually obtained, is not the weight of a 
cubic foot in ounces avoirdupoise, which it certainly ought to be, and par- 
ticularly where the information is intended for the use of practical men. 
If Mr. Rennie were to try any of his specimens, he would -ind the weight 
of a cubic foot much below the numbers he has given in the case of brick, 
volite, and sandstones. The specific gravity of a minute concretion of 
Portland stone may be 2°432, or as Kirwan has it 2°461, but that of the 
stone itself is much lower. 
Were the real specific gravity of porous stones taken, their comparative 
heaviness would become a more decisive mineral character than it is ac- 
cording to the present method, and the correction presents nu difficulty.— 
als 
* 
