on the Strength of Materials. 175 
The same quantity of metal in the feather-edged bar, was not 
so Strong as in the 4 inch bar. 
The semi-elliptical bar, exceeded the 4 inch bar, although 
taken out of it. The parabolic bar came near it. 
The bar made fast at both ends, I suspect must have yielded, 
although the ends were made fast by iron straps. The experi- 
ments from Emerson, on solids of different forms, might be made; 
but the time and trouble these experiments have already cost, 
have compelled me to relinquish further pursuits for the present. 
If, however, in the absence of better, they are worthy of the in-- 
dulgence of the Royal Society, it will not only be a consolation 
to me that my labours merit their attention, but a further in- 
ducement to prosecute the investigation of useful facts, which, 
even in the present advanced state of knowledge, will yet admit 
of addition*. 
I am, with much respect, 
GeorGE RENNIE. 
Since my return to England, I find that a set of experiments 
have been undertaken by Mr. Peter Barlow, of the Royal Mili- 
tary Academy. They are very interesting, ‘but contain no ex- 
periments on the repulsive power of bodies, and consequently, 
my communication is not altogether superseded, although a space 
of seven months has elapsed since this was written. 
London, Dec. 28, 1817. G. R. 
* The science of construction is yet in its infancy, and certainly requires 
many additions. The first experiments on the strength of materials appear 
to have been made before the Royal Society; and there can be no duubt 
that a favourable reception will be given to any others that will tend to 
elucidate a subject, which is likely to form one of the principal branches 
of an engineer’s education ; as be must either proceed on the principle 
of science, or be directed by a feeling of fitness which is to be acquired 
only by devoting a life-time to the practice of his art. It is to be hoped, 
that Mr. Rennie will speedily bring forward some additions to the valuable 
experiments he has already made, with more detailed descriptions of the 
phenomena observed in the course of his labours. he example of the 
chemists ought to be followed, as it is not the number but the accuracy 
and correct description of experiments that constitute their value. Mr. 
Barlow has represented some of the fractures in his experiments by en- 
gravings, which is certainly an excellent plan. 
In Evelyn's Sifva (Dr. Hunter’s edition, vol. ii. p. 227) it is stated that 
a treatise on duplicate proportion was published by Sir William Petty, in 
which is “A new hypothesis of elastic or springy bodies, to show the strengths 
of timbers, and other homogeneous materials applied to buildings, ma- 
chines, &c.” LT have never been able to procure the work ; butif any of 
your correspondents could furnish a sketch of this New Hypothesis,” it 
would be a desirable addition to the history of this branch of science ; as, 
if it should accord with Evelyn's description, our countryman will nauk 
amongst the first contributors to the resistance of solids.—T. T. 
XXVIT. Dis. 
