268 Proceedings of the Royal Society. 
and a scale for weights was suspended from the middle of the 
length of the bar, by a cylindrical steel pin, 2 inch diameter. To 
measure the flexure, a quadrantal piece of mahogany was attached 
to the frame with a vertical bar sliding in two guides at its edge, 
and moving an index. The bar and index were so balanced, that 
one end of the bar bore with constant pressure upon the specimen, 
and the graduated arc was divided into inches, tenths, and 
hundredths, and thousandths were measured by a Vernier. Abar 
of blistered steel, of file hardness, 13 inches long between the 
supports, underwent no permanent alteration of form when loaded 
with 110lbs. The temper of the bar was then successively lowered, 
and it was ultimately again hardened, but in these different states 
its flexure and resistance to permanent change of form remained 
the same. These experiments were repeated with bars of other 
dimensions, which were loaded till they broke, and from them the 
author also infers that the elastic force of steel is not altered by 
temper, and that the force which produces permanent alteration is 
to that which causes fracture in hard steel, as 1 : 1.66, and in the 
same steel, of a straw-yellow temper, 1: 2.56. From comparisons 
of the strain required to cause permanent alteration in different 
kinds of steel, the author concludes, that in the process of hard- 
ening, the particles are put into a state of tension among themselves, 
which lessens their power to resist extraneous force, and the phe- 
nomena of hardening may be referred to the more rapid abstraction 
of heat from the surface of the metal, than can be supplied from 
the internal parts; whence a contraction of the superficial parts 
round the expanded central ones, and a subsequent shrinking of 
the latter, by which the state of tension is produced. 
Thursday, April 1, and Thursday, April 8. 
The following papers were read: 
A Comparison of Barometrical Measurement with the Trigonometrical 
Determination of a Height at Spitzbergen. By Capt. Edward 
Sabine, F. R. 8. 
The hill selected’ for this comparative measurement was the 
highest within convenient distance, of which the ascent was prac- 
