168 Account of Experiments made 
The experiment made by M. Prony (which asserts, that by 
making a slight incision with the file, the resistance is diminished 
one half,) was tried on a j inch bar of English iron; the result 
was 2920 lbs., not a sixth part less. ; 
This single experiment, however, does not sufficiently disprove 
the authority of that able philosopher, for an incision is but a 
vague term. The incision | made might be about the 40th part 
of an inch. 
Experiments on the Twist of } Inch Bars. 
To effect the operation of twisting off a bar, another appa- 
ratus was prepared: it consisted of a wrought-iron lever two feet 
long, having an arched head about 1-6th of a circle, of four feet 
diameter, of which the lever represented the radius, the centre 
round which it moved had a square hole made to receive the end 
of the bar to be twisted. The lever was balanced as before, and 
a scale hung on the arched head ; the other end of the bar being 
fixed in a square hole in a piece of iron, and that again in a vice. 
The undermentioned weights represent the quantity of weight 
put into the scale. 
May 30, 1817. 
On twists close to the bearing, cast horizontal. 
No. Ibs. oz. 
5& 1 in bars, twisted as under with .. 10 14 inthescale. 
59 4 do. bad casting 3% aacdive. “4 
60 dda: se a5 so AOKI 
Average 9 15 
Cast vertical. 
Sl2o. , es Ey Siete) a 5 
Ce ae Af ihe 7 ate A 
63 i... big os ais ee 5 ae 
10 10 
On different metals. 
64 Cast steel .. Le sido BR 28 
65 Shear steel ae ae sich, Pages 
66 Blister steel me ae ef AGLI 
67 English iron, wrought ee at (ADs 
68 Swedish iron, wrought .. chee AB RG 
increase from the ends towards the middle in a ratio sensibly proportional 
to the square of the distance from the end. This fact is at variance with 
the received opinion respecting this strain. 
Dr. Thomson has remarked (Aunals of Philosophy, vol. xii. p. 450), that 
the strengths of English and Swedish iron are not in the same proportion, as 
is found by comparing Count sickengen’s with that described in the Annals 
for April 1816. But, if I do not mistake, Sickengen’s was made on wire, 
and consequently would be bigher, as the strength is always much increased 
by forging, wire-drawing, &c.—Y. T. 
69 Hard 
