for Señor Willis to tell us what to do, I will prepare this for us.’
He poured the coca leaves into a saucer and began to grind them, using the back of a spoon as a pestle. The leaves were brittle and dry and broke up easily. When he had ground them to a powder he added lime and continued to grind until the two substances were thoroughly mixed. Then he put the mixture into an empty tin and added water, stirring until he had a light green paste. He took another tin and punched holes in the bottom, and, using it as a strainer, he forced the paste through.
He said, ‘In any of the villages round here you can see the old women doing this. Will you get me some small, smooth stones?’
Forester went out and got the stones and Rohde used them to roll and squeeze the paste like a pastrycook. Finally the paste was rolled out for the last time and Rohde cut it into rectangles with his pocket-knife. ‘These must dry in the sun,’ he said. ‘Then we put them back in the bags.’
Forester looked dubiously at the small green squares. ‘Is this stuff habit-forming?’
‘Indeed it is,’ said Rohde. ‘But do not worry; this amount will do us no harm. And it will give us the endurance to climb the mountains.’
Willis came back. ‘We can swing it,’ he said. ‘We’ve got the material to make this – what did Armstrong call it?’
‘A trebuchet,’ Forester said.
‘Well, we can do it,’ said Willis. He stopped and looked down at the table. ‘What’s that stuff?’
Forester grinned. ‘A substitute for prime steak; Miguel just cooked it up.’ He shook his head. ‘Medieval artillery and pep pills – what a hell of a mixture.’
‘Talking about steak reminds me that I’m hungry,’ said Willis. ‘We’ll eat before we get started.’
They opened some cans of stew and prepared a meal. As Forester took the first mouthful, he said, ‘Now tell me – what the hell is a trebuchet?’
Willis smiled and produced a stub of pencil. ‘Just an application of the lever,’ he said. ‘Imagine a thing like an out-of-balance seesaw – like this.’ Rapidly he sketched on the soft pine top of the table. ‘The pivot is here and one arm is, say, four times as long as the other. On the short arm you sling a weight, of, say, five hundred pounds, and on the other end you have your missile – a twenty-pound rock.’
He began to jot down calculations. ‘Those medieval fellows worked empirically – they didn’t have the concepts of energy that we have. We can do the whole thing precisely from scratch. Assuming your five-hundred-pound weight drops ten feet. The acceleration of gravity is such that, taking into account frictional losses at the pivot, it will take half a second to fall. That’s five thousand foot-pounds in a half-second, six hundred thousand foot-pounds to the minute, eighteen horse-power of energy applied instantaneously to a twenty-pound rock on the end of the long arm.’
‘That should make it move,’ said Forester.
‘I can tell you the speed,’ said Willis. ‘Assuming the ratio between the two arms is four to one, then the … the …’ He stopped, tapped on the table for a moment, then grinned. ‘Let’s call it the muzzle velocity, although this thing hasn’t a muzzle. The muzzle velocity will be eighty feet per second.’
‘Is there any way of altering the range?’
‘Sure,’ said Willis. ‘Heavy stones won’t go as far as light stones. You want to decrease the range, you use a heavier rock. I must tell O’Hara that – he’d better get busy collecting and grading ammunition.’
He began to sketch on the table in more detail. ‘For the pivot we have the back axle of a wrecked truck that’s back of the huts. The arms we make from the roof beams of a hut. There’ll have to be a cup of some kind to hold the missile – we’ll use a hub-cap bolted on to the end of the long arm. The whole thing will need a mounting but we’ll figure that out when we come to it.’
Forester looked at the sketch critically. ‘It’s going to be damned big and heavy. How are we going to get it down the mountain?’
Willis grinned. ‘I’ve figured that out too. The whole thing will pull apart and we’ll use the axle to carry the rest of it. We’ll wheel the damn thing down the mountain and assemble it again at the bridge.’
‘You’ve done well,’ said Forester.
‘It was Armstrong who thought it up,’ said Willis. ‘For a scholar, he has the most murderous tendencies. He knows more ways of killing people – say, have you ever heard of Greek fire?’
‘In a vague sort of way.’
‘Armstrong says it was as good as napalm, and that the ancients used to have flame-throwers mounted on the prows of their warships. We’ve done a bit of thinking along those lines and got nowhere.’ He looked broodingly at his sketch. ‘He says this thing is nothing to the siege weapons they had. They used to throw dead horses over city walls to start a plague. How heavy is a horse?’
‘Maybe horses weren’t as big in those days,’ said Forester.
‘Any horse that could carry a man in full armour was no midget,’ Willis pointed out. He spooned the last of the gravy from his plate. ‘We’d better get started – I don’t want to work all night again.’
Rohde nodded briefly and Forester looked over at Peabody, snoring on the bunk. ‘I think we’ll start with a bucket of the coldest water we can get,’ he said.
IV
O’Hara looked across the gorge.
Tendrils of smoke still curled from the burnt-out vehicles and he caught the stench of burning rubber. He looked speculatively at the intact jeep at the bridgehead and debated whether to do something about it, but discarded the idea almost as soon as it came to him. It would be useless to destroy a single vehicle – the enemy had plenty more – and he must husband his resources for more vital targets. It was not his intention to wage a war of attrition; the enemy could beat him hands down at that game.
He had been along the edge of the gorge downstream to where the road turned away, half a mile from the bridge, and had picked out spots from which crossbowmen could keep up a harassing fire. Glumly, he thought that Armstrong was right – the enemy would not be content to be docile targets; they would certainly take steps to protect themselves against further attack. The only reason for the present success was the unexpectedness of it all, as though a rabbit had taken a weasel by the throat.
The enemy was still vigilant by the bridge. Once, when O’Hara had incautiously exposed himself, he drew a concentrated fire that was unpleasantly accurate and it was only his quick reflexes and the fact that he was in sight for so short a time that saved him from a bullet in the head. We can take no chances, he thought; no chances at all.
Now he looked at the bridge with the twelve-foot gap yawning in the middle and thought of ways of getting at it. Fire still seemed the best bet and Willis had said that there were two drums of paraffin up at the camp. He measured with his eye the hundred-yard approach to the bridge; there was a slight incline and he thought that, given a good push, a drum would roll as far as the bridge. It was worth trying.
Presently
