At last Canterel decided to avail himself of a discovery he had made all by himself several years before and which had always yielded excellent results in practice.

This concerned a curious system for the extraction of teeth, which avoided the dangerous and harmful use of anesthetics. After long research Canterel had obtained two highly complex metals: when these were brought into contact, they instantly created an irresistible and specialized magnetic force operating exclusively on the calcareous element of which human teeth are made.

One of the metals was gray; the other had a steel-blue luster. From each of them he cut a disc of one millimeter radius, then fixed the gray one to a slender, rigid handle slightly oblique to its plane — and drove the tips of three short, horizontally diverging rods into the blue one’s rim at symmetrically equal distances. The other ends of these were attached to the upper circumference of a small cylinder fitted with a slender handle. When the time came, he used both hands independently to introduce the cylinder into the patient’s mouth, resting its thick, blunt, lower rim on the two teeth either side of the one to be removed — then brought up the gray disc and laid it accurately against the blue one. At once the magnetism came into play, so abruptly and powerfully that the decayed tooth left its socket in answer to the summons without giving the person concerned time to notice the slightest shock of pain. It entered the cylinder, which, being made entirely of platinum like the three rods, was capable of withstanding any ordeal, and flew to the blue disc. When dealing with the lower jaw the cylinder was placed upright, with the blue disc above; on the other hand, when the upper jaw was involved, the operation, though similar, made it necessary to place the cylinder and the gray ring in reverse position. For mouths ill-provided with teeth, if there was no support on one side because a tooth was missing, the professor would make use of a very simple device, selecting a right-angled parallelepiped, high enough to provide the best substitute, from a varied collection made of solid ivory. In this way the cylinder, supported by a tooth on one side and the ivory on the other, offered the necessary resistance. Two parallelepipeds were required when the decayed tooth was surrounded by a complete void so that it was doubly isolated. Confronted by two supporting teeth of unequal size, Canterel had recourse to an assortment of small ivory squares of various thicknesses; a single one of these laid on the lower tooth made their levels perfectly equal during the critical moment.

An intentional consequence of the special atomic combination which generated the magnetism was that it only operated on the darkened inner side where the cylinder began, strictly within the field of a flawless imaginary tube of indefinite length, with its axis passing through the center of the two discs and with a diameter equal to theirs. So there was no danger of the gray disc attracting a tooth from the wrong jaw, and the blue one only exerted its effect on part of the tooth at which it was aimed, without causing the slightest disturbance to its neighbors. In view of its extraordinary intensity, this circumscribed action was sufficient to produce the desired result, quite painless because so sudden. When the tooth had been extracted and was adhering to the blue disc, Canterel immediately took the gray disc away; for the magnetism would have produced its effect in spite of the obstacle — as he had ascertained from his experiments — and he was afraid of it accidentally wreaking havoc on a healthy part of the jaw should the patient, or he himself, make a false move.

The process, which soon became well known, brought a stream of visitors suffering from toothache to Locus Solus, who all went away delighted by the comfort and dispatch with which the cause of their suffering was removed, without their experiencing the slightest painful jolt.

The discarded teeth loosened by the professor’s skill were piled up higgledy-piggledy, and he had never had an opportunity to deal with this embarrassing stock, the disposal of which had been constantly postponed.

After hatching his new scheme, he blessed the successive delays that had put a usable and practical medium within reach. He resolved to devote his supply of teeth to the execution of his mosaic. They were varied enough in shape and color to lend themselves to this fantasy, and an enriching complexity would be provided both by the more or less vivid bloodstains on the roots and the brilliant luster of the gold caps and fillings.

The professor delicately attached two new discs, similar to those used in his dental operations, to the bottom of his paving beetle, between three supporting claws. But this time he regulated the composition of the two metals so as to set up a much weaker magnetic field; for indeed it was only a matter of picking up teeth that were simply strewn on the ground, without any need to extract them from their sockets. As they flew through the air, conveying their light spoils from one place to another, a pair of discs as powerful as the original ones would have snapped up any teeth on the ground touched by their magnetic field, with each newcomer leaping up to fasten itself beneath its predecessors; but there was no danger of this supreme inconvenience occurring because the new discs, though identical with the first in size and individual shade, had only just power enough to summon an unresisting tooth at very close range. A chronometer fitted to the bottom of the aluminium bar operated a vertical rod which caused the two metals to join or separate alternately, at certain precise moments, thereby making the magnetism intermittent.

Canterel would have obtained similar results by using variously colored pieces of soft iron for his mosaic; an electromagnet could easily have picked these up, then dropped them, by means of a discontinuous current. But this process would have called for the arduous installation in the flying punner of a weighty system of batteries, which would have been attended by many serious disadvantages.

So the professor preferred his first idea which, while exploiting in an original manner the previous discovery, of which he was justly proud, also attracted him because of the novelty the projected picture would derive from the use of fragments shaped and colored entirely by chance, with no artistic desire or premeditation.

After completing the punner by the addition of the giant compass needle, Canterel found that he still had one indispensable condition to fulfil. It was necessary for the roving apparatus to be capable of remaining perfectly erect during its intervals of repose in the various regions of the future work. Now the further the mosaic progressed, the greater was the risk of the three claw supports encountering teeth as they came to rest, and upsetting the general equilibrium; by leaning over, the paving beetle would seriously compromise the very precise orientation of the mirrors with their regular motions, and any further ascent would become impossible.

To settle this vitally important matter, Canterel made the lower part of the three claws hollow and fitted each with a diminutive chronometer, whose clockwork, at the appropriate moment, was to activate a special internal needle with a rounded tip, capable of being temporarily lowered. Whenever a claw was about to alight on a tooth already forming an integral part of the mosaic, the other two would be lengthened beforehand by their respective needles, whose tips would reach the ground. Sometimes two claws would settle on teeth and only the third would use its needle.

The fine supplementary rods would protrude to a greater or lesser extent, according to the level of the teeth, whose thickness was very variable. Indeed, the molars and incisors, adult teeth and milk teeth, once set out would provide an immense variety of heights, which the individual characteristics of each jaw would increase. This fact would not harm the final result, since the mosaic’s artistic vigor would not suffer from a mere unevenness of its surface; but in order to regulate the three needles chronometrically, Canterel would be forced to make an additional major calculation. Between the grinder of a man and the incisor of a child, to take the two extremes, the relative difference in level would be considerable and, depending on which of the two was chosen by the claws, the two remaining ones would have to make their internal appendices go a longer or shorter way to reach the ground; furthermore, whenever the two claws were simultaneously aimed at two teeth of different thickness, one of them would have recourse to its needle. During the final days, when some isolated gap was being filled and the three claws swooped down together on three teeth, one would often observe that one or two of the mobile accessories were involved, despite the fact that there was no contact with the ground at all.

Given these various characteristics, the adjusting of the three lowest chronometers could hardly fail to be an exceptionally arduous task. Fortunately the professor only had to concern himself, as far as the needle extensions were concerned, with the actual site of the mosaic and not with what lay around it.