182 ENQUIRY INTO THE STRENGTH AND 
manently bear without endangering its security: 
This was an exceedingly important question, 
which in order to solve, we came to the conclu- 
sion of putting to the test of experiment. 
For this purpose ten bars were procured, each 
cast to be one inch square, and having loaded 
them with different weights,—some nearly ap- 
proaching the breaking point,—and supported 
theirends on props 4 ft. 6in. asunder,—they were 
left in this position to determine how long they 
would support the loads without breaking. Five 
weeks have now-elapsed since they were charged, 
and, from what we can at present observe, there 
is every appearance of a long and tedious experi-~ 
ment.* I should here mention that the deflec- 
tions are taken weekly, in order to determine 
the alterations in the state of the bars. 
* Since the above was written, one of the bars has given way 
and broken near the centre, after having sustained a load of 448 
Ibs. for 37 days. The deflection was observed to have increased 
from 1.904 to 2.014 between the time of loading and that of 
the last measurement, three days before the rupture took place. 
It must be observed that this bar was thinner than any of the 
others now tried, and had borne for this period a weight larger 
than had broken bars of the same size in previous experiments 
upon this iron, when the weights were laid on without loss of 
time. All the other bars continue to sustain their loads, though 
they have born them for many months; the deflections however 
are slightly on the increase. The particulars of these will be 
given in the Seventh Report of the British Association for the 
Advancement of Science. 
