Machines with which artillery-spotting was done were usually manned by a pilot and an observer, so that the latter could devote his entire attention to noting the fire of the guns and signaling ranges without being hampered by having to drive the machine. These machines were usually of the pusher type, so that the observer could have an unobstructed view. They did not have to be fast machines. It was really better for them to move slowly. Had it been possible for them to stop altogether and hover over the spot that was being shelled, it would have been a distinct advantage. That would have given the observer a chance to note with better accuracy the fall of the shell. Like the scout, the spotter had to be a fast climber, so that it could get out of the range of enemy guns and run away from attacking planes. GIANTS OF THE SKY The largest war-planes were the bomb-dropping machines. They had to be capable of carrying heavy loads of explosives. They were usually slow machines, speed being sacrificed in carrying-capacity. The Germans paid a great deal of attention to big bomb-dropping machines, particularly after their Zeppelins proved a failure. Their huge Gothas were built to make night raids on undefended cities. The Italians and the British retaliated with machines that were even larger. At first the French were inclined to let giant planes alone. They did not care to conduct long-distance bombing-raids on German cities because their own important cities were so near the battle-front that the Germans could have done those places more harm than the French could have inflicted. Later they built some giant machines, although not so large as those of the Italians and the British. The large triplane Capronis built by the Italians held a crew of three men. They were armed with three guns and carried 2750 pounds of explosives. That made a useful load of 4000 pounds. The machine was driven by three engines with a total of 900 horse-power. The big British plane was the Handley-Page, which had a wing-spread of 125 feet and could carry a useful load of three tons. These enormous machines conducted their raids at night because they were comparatively slow and could not defend themselves against speedy battle-planes. The big Italian machines used "search-light" bombs to help them locate important points on the ground beneath. These were brilliant magnesium torches suspended from parachutes so that they would fall slowly and give a broad illumination, while the airplane itself was shielded from the light by the parachute. But these giants were not the only bombing-machines. There were smaller machines that operated over the enemy's battle-line and dropped bombs on any suspicious object behind the enemy lines. These machines had to be convoyed by fast battle-planes which fought off hostile airmen. HOW FAST IS A HUNDRED AND FIFTY MILES PER HOUR?