SCIENTIFIC SUMMARY. 
117 
Boiler Explosions . — The Astronomer Royal communicated to the British 
Association an important paper on the percussive theory of boiler explo- 
sions, to which reference has previously been made in these pages. Accord- 
ing to that theory, the destructive effects observed in boiler explosions 
are not due to the pressure first causing rupture, but to the subsequent 
sudden generation of steam in the heated mass of water, from which the 
pressure has been removed. Professor Airy has obtained, from data fur- 
nished by the experiments of Professor Miller of Cambridge, an accurate 
numerical expression for the destructive energy of the steam. He concludes 
that, in the case of a boiler working at 60 lb. pressure, each cubic foot of 
water has the same destructive energy as a pound of gunpowder. Now, many 
boilers in use contain 600 cubic feet of water ; hence the fearful devastation 
caused by their rupture may be imagined. An important practical deduc- 
tion from Professor Airy’s calculations, is that the destructive effects of a 
boiler explosion are proportional to the quantity of water in the boiler. 
Trial of Steam Fire-Engines. — A competitive trial of steam fire-engines 
took place at the Crystal Palace. Steam was raised to 100 lb. pressure, 
starting from cold water, in from 10^ to 17 minutes by different engines. 
The experiments comprised : — (First Trial) — Delivery of 1,000 gallons 
into a tank 67 feet distant and 27° from the horizontal, commencing with 
cold water in the boiler. (Second Trial) — Like the first, but commencing 
with steam at 100 lb. pressure. (Third Trial) — Delivery through 440 
feet of hose into a tank, through an aperture 0 feet in diameter, placed 
40 feet horizontally and 40 feet vertically from the nozzle. (Fourth 
Trial) — Vertical discharge, in which two of the engines attained a height 
of 180 feet. The results are given in the following table, calculated by 
a correspondent of the Engineer , from the official tables : — 
Makers. 
Weight. 
Heating 
surface. 
Gallons delivered 
per min. 
Gallons per min. 
per sq. ft. of heating 
surface. 
Gallons per lb. 
weight of Engine. 
lbs. 
sq. ft. 
1st 
Trial. 
2nd : 
Trial. 
3rd 
Trial. 
1st 
Trial. 
2nd 
Trial. 
3rd 
Trial. 
1st 
Trial. 
2nd 
Trial. 
3rd 
Trial. 
Merry weather . . 
6594 
207 
103 
321 
216 
•49 
1-55 
l-oi 
•0158 
•0492 
•033 
Shand & Mason. . 
6412 
128 
97 
333 
122 
751 
2-6 
•95 
•0151 
•0519 
*019 
Easton & Amos. . 
6592 
210 
159 
•757 
•0241 
Bull & Co 
6 052 
200 
147 
327 
254 
•73 
1*63 
1-27 
•0243 
•054 
•0419 
Roberts 
4400 
141 
49 
91 
*34 
•64 
•0111 
•0206 
Shand & Mason. . 
3304 
624 
185 
176 
135 
2-9 
2-8 
2 1 
•055 
•053 
•041 
Merryweather . . 
3490 
644 
108 
159 
81 
1-6 
2-4 
1-2 
•031 
•046 
•023 
Lee & Co 
3360 
106 
165 
172 
71 
1-5 
1-6 
0-66 
•049 
•051 
•021 
MEDICAL SCIENCES. 
Absorptive Power of the Healthy Human Shin . — This is a very serious 
question, especially as regards Continental practice. The absorption of 
medicaments has been for a long time under the consideration of M. 
Delore, who now makes known his opinions on the subject. He believes 
that the healthy skin is capable of absorbing all substances soluble in 
