SCIENTIFIC SUMMAET. 
101 
prove, in a paper read before the Society of Engineers, that the endurance of 
ordnance is closely dependent on the ratio of the mass of the breech to the 
mass of the barrel. The greater the mass of the breech the greater the 
endurance of the gun. The following table gives some of the facts on which 
Mr. Rigg founds his theory : — 
Ratio of Mass of 
p Metal ill Breech No. of Rounds 
to Mass of Metal before bursting 
in Barrel 
English cast-iron 68-pr 
1 to 
41 . 
, 2,000 to 4,000 
Whitworth 70-pr 
1 
17 
111 
Coils slipped. 
Armstrong 300-pr 
1 
7 
264 
Breech blown off. 
American Dahlgren 30-pr 
1 
21 . 
. 2,000 
Not burst. 
„ Parrott 200-pr . 
1 
9 . 
230 
„ Parrott 30-pr 
1 
m . 
. 4,606 
These facts, which are the most important of those quoted by Mr. Rigg, 
culled from his paper and arranged for comparison, would seem to bear the 
interpretation of the relative weakness of heavy gims as well as that which 
Mr. Rigg founds on them. But there is probably some truth in Mr. Rigg’s 
theory, that a heavy breech absorbs the blow of the explosion and lessens the 
longitudinal strain. It certainly appears that improved modes of construct- 
ing guns, whilst adding greatly to the power of the barrel to resist bursting, 
have in some cases dangerously diminished the longitudinal strength. 
Road Locomotives. — Mr. R. "W. Thomson, of Glasgow, is using india- 
rubber tires 12 inches wide and 5 inches thick, for road locomotives, with 
great success. With these tires the engine passes easily over the softest and 
roughest ground ; and, strange to say, the tire shows no signs of wear. 
A Simple Fire-Escape . — We so often hear of, in cases of fire in dwellings, 
the inmates throwing themselves as a dernier ressort out of windows, and 
their sustaining serious injury, that the suggestion of one of our correspond- 
ents seems worthy of notice. H. B. writes: Would you allow me to 
suggest whether a belt attached to a strong rope wound round as measuring- 
tapes are on a reel, the said reel having an iron ring attached (something in 
the plan of those on which keys are put) so as to admit of the ring being 
fastened round a bedpost, or leg of a chest of drawers, &c., might not afford 
in time of extreme necessity a chance of escape — the rope to which a person 
was attached by the belt running out as the jump from a window was 
made, and able to be pulled up by any other unfortunate when it was de- 
tached ? Of course the experiment would be a last resort, but might it not 
afford a possibility of escape at very trifling expense ?” 
MEDICAL SCIENCE. 
The Functions of the Pancreas . — At the meeting of the Royal Society, on 
the 12th of December, a paper by Dr. Dobell was read, in which the 
author described the results of his experiments with the extract of the pan- 
creas upon fat. He proposes to give the term pancreatine to all those ex- 
tracts of the gland which possess the power of emulsifying fatty matter. He 
found that the secretion was frequently acid. At the conclusion of the 
