With this he took up the letters which Thorndyke had sealed and stamped and reluctantly withdrew, not without a last, wistful glance at the apparatus on the tray.
As the door closed behind him, Thorndyke rose, and, bringing forth the button from the drawer in which he had bestowed it, began operations at once. First, with a pair of fine forceps he carefully picked off the worm-tube half-a-dozen of the largest fragments and laid them on a glass slide. This he placed on the stage of the microscope and, having fitted on a two-inch objective, made a preliminary inspection under various conditions of light, both transmitted and reflected. When he had got clearly into his mind the general character of the unknown rock, he fetched from a store cabinet in the office a number of shallow drawers filled with labelled specimens of rocks and minerals; and he also placed on the table in readiness for reference one or two standard works on geology and petrology. But before examining either the books or the specimens in the drawers, he opened out a geological chart of the British Isles and closely scrutinized the comparatively small area with which the button was concerned—the Land’s End and the North and South Coasts of Cornwall. A very brief scrutiny of the map showed him that the enquiry could now be narrowed down to a quite small group of rocks, the majority of which he could exclude at once by his own knowledge of the more familiar types; which was highly satisfactory. But there was evidently something more than this. Any one who should have been observing him as he pored over the chart, would have seen, by a suddenly increased attention, with a certain repressed eagerness, that some really illuminating fact had come into view; and his next proceedings would make clear to such an observer that the problem had already changed from one search to a definite and particular identification. From the chart he turned to the drawers of specimens, running his eye quickly over their contents as if looking for some specific object; and this object he presently found in a little cardboard tray—a single fragment of a grey, compact rock, which he pounced upon at once, and picking it out of its tray, laid it on the slide with the fragments from the worm-tube. Careful comparison gave the impression that they were identical in character, but the great difference in the size of the fragments compared was a source of possible error. Accordingly he wrapped the specimen lightly in paper, and with a hammer from the tool-drawer struck it a sharp blow, which broke it into a number of smaller fragments, some of them quite minute. Picking out one or two of the smallest from the paper, and carefully noting the “conchoidal” character of the fracture, he placed them on a separate slide which he at once labelled “stock specimen,” labelling the other slide “worm-tube.” Having taken this precaution against possible confusion, he laid the two slides on the stage of the microscope and once more made a minute comparison. And again the conclusion emerged that the fragments from the worm-tube were identical in all their characters with the fragments of the stock specimen.
It now remained to test this conclusion by more exact methods. Two more labelled slides having been prepared, Thorndyke laid them, label downwards, on the table and dropped on each a large drop of melted Canada balsam. In one drop, while it was still soft, he immersed two or three fragments from the worm-tube; in the other a like number of fragments of the stock specimen. Then he heated both slides over a spirit lamp to liquefy the balsam and completely immerse the fragments, and laid them aside to cool while he prepared the appliances for grinding the sections.
This process was, as Polton had hinted, a rather tedious one. It consisted in rubbing the two slides backwards and forwards upon a wetted Turkey stone until the fragments of rock were ground to a flat surface. The flattened surfaces had then to be polished upon a smoother stone and when this had been done, the slides were once more heated over the spirit lamp, the balsam liquefied, and each of the fragments neatly turned over with a needle on its flat side. When the balsam was cool and set hard, the grinding process was repeated until each of the fragments was worn down to a thin plate or film with parallel sides. Then the slides were again heated, a fresh drop of balsam applied and a cover-glass laid on top. The specimens were now finished and ready for examination.
On this, the final stage of the investigation, he bestowed the utmost care and attention. The two specimens were examined exhaustively and compared again and again by every possible method, including the use of the polariscope and the spectroscope; and the results of each observation were at once written down. Finally, Thorndyke turned to the books of reference, and selecting a highly technical work on petrology, checked his written notes by the very detailed descriptions that it furnished of rocks of volcanic origin. And once again the results were entirely confirmatory of the opinion that he had at first formed. No doubt whatever was left in his mind as to the nature of the particles of rock of which the worm had built its tube. But if his opinion was correct, he held evidence producible in a court of law that Daniel Purcell had never landed at Penzance; that, in fact, his dead body was even now lying at the bottom of the sea.
As he consumed his frugal supper Thorndyke turned over the situation in his mind. He had no doubts at all. But it would be necessary to get his identification of the rock confirmed by a recognized authority who could be called as a witness and whose statement would be accepted by the court as establishing the facts. There was no difficulty about that. He had a friend who was connected with the Geological Museum and who was recognized throughout the world as a first-class authority on everything relating to the physical and chemical proprieties of rocks and minerals. He would take the specimens to-morrow to this expert and ask him to examine them; and when the authoritative opinion had been pronounced, he would consider what procedure he should adopt. Already there was growing up in his mind a doubt as to the expediency of taking action on purely scientific evidence; and in answer to that doubt a new scheme began to suggest itself.
But for the moment he put it aside. The important thing was to get the expert identification of the rock and so put his evidence on the basis of established fact. The conversion of scientific into legal evidence was a separate matter that could be dealt with later. And having reached this conclusion, he took a sheet of note paper from the rack and wrote a short letter to his friend at the museum making an appointment for the following afternoon. A few minutes later he dropped it into the box of the Fleet Street Post Office and for the time being dismissed the case from his mind.
Chapter XIV.
In Which Mr. Varney Is Disillusioned
Thorndyke’s visit to the Geological Museum was not a protracted affair, for his friend, Mr. Burston, made short work of the investigation.
“You say you have examined the specimens yourself,” said he. “Well, I expect you know what they are; just come to me for an official confirmation, hm? However, don’t tell me what your conclusion was. I may as well start with an open mind. Write it down on this slip of paper and lay it on the table face downwards. And now let us have the specimens.”