ADDRESS. 23 
last year in the interesting lecture of Roberts-Austen, has been, 
and is still being, pursued by accomplished workers, among whom the 
most prominent is I’. Osmond. The phenomenon of recalescence, or 
the re-glowing of, or liberation of heat in, iron and steel at certain 
stages during the cooling process, first examined into by Barrett, appears 
to be the result of actual chemical combination between the metal and its 
contained carbon at the particular temperature attained at the time; 
while the absorption of heat, demonstrated by the arrest in rise of 
temperature during its continuous application to the metal, is ascribed 
to the elimination, within the mass, of carbon as an iron-carbide per- 
fectly stable at low temperatures. The pursuit of a well-devised system 
of experimental inquiry into this subject has led Osmond to propound 
theories of the hardening and tempering of steel, which are at present 
receiving the careful study of physicists and chemists, and cannot fail 
to lead to further important advancement of our knowledge of the true 
nature of the influence of carbon upon the properties of iron. 
Another important subject connected with the treatment of masses of 
steel, and with the influence exercised upon their physical characteristics 
by the processes of hardening and tempering, and by submitting them to 
oft-repeated concussions or vibrations, or to frequent or long-continued 
strains, is the development and maintenance, or gradual disappearance, 
of internal stresses in the masses—one of the many important subjects to 
which attention was directed by Dr. Anderson, the Director-General of Ord- 
nance Factories, in his very suggestive Address to the Mechanical Section 
last year. This question is one of especial interest to the constructor 
of steel guns, as the powers of endurance of these do not simply depend 
upon the quality of the material composing them, but are very largely 
influenced by the treatment which it receives at the hands of the gun- 
maker. Indeed, the highest importance attaches to the processes which 
are applied to the preliminary preparation of the individual parts used 
in constructing the gun, and to the putting together of these so as 
to ensure their being and remaining in the physical condition best cal- 
_ culated to assist each other in securing for the structure the power of so 
successfully resisting the heavy strains to which it has to be subjected, as 
to suffer little alteration other than that due to the superficial action of 
the highly-heated products of explosion of the charges fired in the gun. 
The development of internal strains in objects of steel, especially by the 
hardening and tempering processes, or by their exposure to conditions 
favourable to unequal cooling of different parts of the mass, has long been 
a subject of much trouble and of experimental inquiry in connection 
with many applications of steel. Systematic experiments of the kind 
commenced, about eighteen years ago, by the late Russian general Kala- 
koutsky, are now being pursued at Woolwich, with the objects of deter- 
mining the nature and causes of internal stresses in steel gun-hoops and 
-tubes, and in shells, and of thereby establishing the proper course to be 
