SCIENTIFIC SUMMARY. 
119 
a favourite explanation of such catastrophes, and fabulous estimates of 
the force of the steam indulged in ; as, for instance, 1,000 lb. per square 
inch in the case of the accident on board the Great Eastern. Mr. Colburn, 
however, has shown that there are two stages in the explosion, — first, a 
rupture at some weakened part of the boiler, and the escape of the con- 
tained steam with extreme rapidity, but without violence ; next, the 
generation of a second volume of steam in the highly-heated water 
suddenly liberated from pressure, which, occurring simultaneously 
throughout the mass, projects that water upwards so as to strike the 
boiler-shell with a force proportional, not to the statical pressure of the 
steam, but to the vis viva accumulated in the flying mass. These two 
stages were accurately observed by an engineer present at the explosion 
of a locomotive boiler on the North-Western Railway, near Rugby, last 
year. He noticed the rush of the steam, followed, after an appreciable 
interval, by the crash of the explosion. 
There remain, however, cases in which it is difficult to find any 
indications of the first rupture assumed by Mr. Colburn. Towards the 
explanation of these, attention has very recently been recalled to the 
experiments of Professor Donny, of the University of Ghent. Professor 
Donny found that if water be completely freed from air its temperature 
can be raised to 275° Fahr. in the open air without ebullition. On con- 
tinuing the application of heat, however, the production of vapour is so 
instantaneous and considerable as to cause an explosion. Now, a large 
number of boiler explosions are known to occur just as an engine which 
has been for some time at rest is first started ; and long-continued boiling 
is one method of expelling the air from water. Under such circum- 
stances, it has been urged, a sudden and violent production of steam may 
ensue, sufficient to determine rupture in boilers known to be safe at their 
working pressure. 
In the French Moniteur Universel occurs the following announcement 
of a new prime mover : — 
“ The Lenoir motor, of which the principle is the dilatation of air 
inflamed by electricity, has just realized the hopes we conceived at the 
time of its first appearance. An engine of six horses’ power, with two 
cylinders, actuates, at the time we write, the presses of the Moniteur 
Universel .” 
Some experiments have just been made at Shoeburyness on the 
penetrative power of shells, the results of which reopen the question 
of the invulnerability of our mail-clad vessels. It has been fully 
established that ordinary cast-iron shells will not perforate even com- 
paratively thin plates of wrought iron, owing to the readiness with 
which they break up ; in fact, the vis viva, instead of being expended 
on the target, is wasted in demolishing the projectile, and that so rapidly, 
that the powder is usually scattered without an explosion. Mr. Whitworth, 
however, has manufactured some shells of cast steel strong enough to resist 
this tendency to disruption, and the result is, that they prove to have even 
higher penetrative power than the ordinary cast-iron solid shot. A 12- 
ponnder shell from a Whitworth gun perforated a 2^ inch, and a 70-pounder 
