The more French thought over the idea, the more probable it seemed. The crate had been thrown into the sea, most likely from the shore and when the tide was ebbing, and it had floated out into the Inlet. By the time it had reached the position in which it was found, enough water had leaked in to sink it.
He wondered if any confirmatory evidence of the theory were available. Then an idea struck him, and walking to the police station, he asked for Sergeant Nield.
‘I want you, sergeant, to give me a bit of help,’ he began. ‘First, I want the weights of the crate and the bar of iron. Can you get them for me?’
‘Certainly. We’ve nothing here that would weigh them, but I’ll send them to the railway station. You’ll have the weights in half an hour.’
‘Good man! Now there is one other thing. Can you borrow a Molesworth for me?’
‘A Molesworth?’
‘A Molesworth’s Pocket Book of Engineering Formulæ. You’ll get it from any engineer or architect.’
‘Yes, I think I can manage that. Anything else?’
‘No, sergeant, that’s all, except that before you send away the crate I want to measure those nail holes.’
French took a pencil from his pocket and sharpened it to a long thin evenly rounded point. This he pushed into the nail holes, marking how far it went in. Then with a pocket rule he measured the diameter of the pencil, the length of the sharpened portion, and the distance the latter had entered. From these dimensions a simple calculation told him that the holes were all slightly under one-sixth of an inch in diameter.
The sergeant was an energetic man, and before the half hour was up he had produced the required weights and the engineer’s pocket book. French, returning to the hotel, sat down with the Molesworth and a few sheets of paper, and began with some misgivings to bury himself in engineering calculations.
First he added the weights of the crate, the body and the steel bar: they came to 29 stone or 406 lbs. Then he found that the volume of the crate was just a trifle over 15 cubic feet. This latter multiplied by the weight of a cubic foot of sea-water—64 lbs.—gave a total of 985 lbs. as the weight of water the crate would displace if completely submerged. But if the weight of the crate was 406 lbs., and the weight of the water it displaced was 985 lbs., it followed that not only would it float, but it would float with a very considerable buoyancy, represented by the difference between these two, or 579 lbs. The first part of his theory was therefore tenable.
But the moment the crate was thrown into the sea, water would begin to run in through the lower holes. French wondered if he could calculate how long it would take to sink.
He was himself rather out of his depth among the unfamiliar figures and formulæ given on the subject. The problem was, how long would it take 579 lbs. of water to run through seven one-sixth inch holes? This, he found, depended on the head, which he could only guess at approximately one foot. He worked for a considerable time, and at last came to the conclusion that it would take slightly over an hour. But that his calculations were correct he would not like to have sworn.
At all events these results were extremely promising, and gave him at least a tentative working theory.
But if the crate had floated from the coast to where it was found, the question immediately arose: At what point had it been thrown in?
Here was a question which could only be answered with the help of local knowledge. French thought that a discussion with the coastguard might suggest ideas. Accordingly he left the hotel and turned towards the harbour with the intention of looking up Manners.
Tom Manners was hoeing in his little garden when French hailed him. He was not a native, but the course of a long career had led him from Shoreditch, via the Royal Navy, to Burry Port. In person he was small, stout, and elderly, but his movements were still alert and his eyes shone with intelligence.
‘I want to have another chat with you about this affair,’ said French, who had already heard the other’s statement. ‘Just walk down to the end of the pier with me while we talk.’
They strolled down past the stumpy lighthouse to where they could get a view of the Inlet.
Again it was a perfect afternoon. The sun, pouring down through a slight haze, put as much warmth as was possible into the somewhat drab colours of the landscape, the steel of the water, the varying browns of the mud and sand, the dingy greys and slate of the town, the greens of the grass and trees on the hills beyond. Some four miles away to the right was the long line of Llanelly, with its chimneys sticking up irregularly like the teeth of a rather badly damaged comb. Fifty-three chimneys, French counted, and he was sure he had not seen anything like all the town contained. Beyond Llanelly the coastline showed as a blur in the haze, but opposite, across the Inlet, lay the great yellow stretch of the Llanrhidian Sands, rising through grey-green dunes to the high ground of the Gower Peninsula.
‘Let us sit down,’ French suggested, when he had assimilated the view. ‘I have come to the conclusion that the crate must have been thrown into the sea at some point along the shore and floated out to where it was found. It would float, I estimate, for about an hour, when enough water would have got in to sink it. Now what I want to know is, where, along the coast, might the crate have been thrown in, so as to reach in an hour the place at which it was found?’
Manners nodded, but did not reply. French unrolled his map and went on: ‘Here is a map of the district, and this is the point at which the crate was found. Let us take the places in turn. If it had been thrown in here at Burry Port, would it have got there in time?’
‘It ain’t just so easy to say,’ Manners declared slowly. ‘It might, if the tide was flowing, and then again it mightn’t. It might ’ave started ’ere or from Pembrey—that’s ’alf a mile over there to the west.’
This was not encouraging, but French tried again.
‘Very well,’ he said. ‘Now what about Llanelly?’
Llanelly, it appeared, was also a doubtful proposition.
‘It’s like this ’ere, Mr French,’ Manners explained. ‘It’s all according to ’ow the tide ’appens to be running. If the tide was flowing and that there crate was dropped in at Llanelly, it would go farther up the Inlet than wot you show on the chart. An’ if the tide was ebbing it would go farther down. But if the tide was on the turn it might go up or down and then come back to the place. You see wot I mean?’
French saw it and he sighed as he saw also that it meant that there was practically no part of the adjacent shores from which the crate might not have come. Then it occurred to him that both his question and Manners’ reply had been based on a misconception.
The murderer’s object was to get rid of the crate. Would he, therefore, choose a rising or half tide which might drift it back inshore? Surely not; he would select one which would take it as far as possible out to sea. French felt that only ebb tides need be considered. He turned again to Manners.
‘I suppose a good ebb develops some strong currents in these channels?’
‘You may say so, Mr French. An average of five knots you may reckon on. A deal faster than you could walk.’
‘Five knots an hour?’
‘No, sir; five knots. It’s like this ’ere. A knot ain’t