Spade

48 Machine-made Ice 72 A Cold Store 80 Dassen Island Lighthouse 88 Measuring Heat 128 The Telewriter 184 A Miners' Rescue Team 208 Pneumatic Hammer Drill 216 An Artificial Coal Mine 224 Sectional view of a 60-pounder Gun 232 Rifles of different Nations 240

DIAGRAMS

---

MARVELS OF SCIENTIFIC
INVENTION

---

CHAPTER I

DIGGING WITH DYNAMITE

Most people are afraid of the word explosion and shudder with apprehension at the mention of dynamite. The latter, particularly, conjures up visions of anarchists, bombs, and all manner of wickedness. Yet the time seems to be coming when every farmer will regard explosives, of the general type known to the public as dynamite, as among his most trusty implements. It is so already in some places. In the United States explosives have been used for years, owing to the exertions of the Du Pont Powder Company, while Messrs Curtiss' and Harvey, and Messrs Nobels, the great explosive manufacturers, are busy introducing them in Great Britain.

It will perhaps be interesting first of all to see what this terror-striking compound is. One essential feature is the harmless gas which constitutes the bulk of our atmosphere, nitrogen. Ordinarily one of the most lazy, inactive, inert of substances, this gas will, under certain circumstances, enter into combination with others, and when it does so it becomes in some cases the very reverse of its usual peaceful, lethargic self. It is as if it entered reluctantly into these compounds and so introduced an element of instability into them. It is like a dissatisfied partner in a business, ready to break up the whole combination on very slight provocation.

And it must be remembered that an explosive is simply some chemical compound which can change suddenly into something else of much larger volume. Water, when boiled, increases to about 1600 times its own volume of steam, and if it were possible to bring about the change suddenly water would be a fairly powerful explosive. Coal burnt in a fire changes, with oxygen from the atmosphere, into carbonic acid gas, and the volume of that latter which is so produced is much more than that of the combined volumes of the oxygen