The scene changes. In what is known as the St. Petersburg quarter, which is situated on the north side of the Neva, is an old and lofty house, not unlike some of the old buildings in Edinburgh.
The house is let out in tenements, and there is a common stair for the use of all the tenants, who for the most part are working men, artisans, and the like. At the very top of the building, immediately under the tiles, is a long room with a slanting roof. In this room three men are at work, busily at work, though it is the dead of night. They carry on their work by lamplight.
Two are seated at a bench, which is covered with a miscellaneous lot of tools—pliers, small hammers, pincers, files, tiny saws, screw-drivers, chisels of various shapes, punches, etc. There are also sets of mathematical instruments; and before the men are carefully-prepared diagrams and drawings to scale, and to these the men make constant reference.
They are fitting together an ingenious and clever piece of mechanism in a small oblong box, lined with tin, and divided into compartments. It is a sort of clockwork arrangement they are engaged upon, and it is intended that the motive power of this mechanism shall be a noiseless spring, acting on a solid brass, notched wheel. In the rim of this wheel are forty-eight notches. The wheel can be made to revolve slowly or quickly, as may be desired. As the wheel revolves, every time a notch reaches a given point, mathematically determined, a tiny, but powerful, steel lever drops into it, and this causes a steel rod, something like a miniature shaft of a screw-steamer, to advance at right angles with the wheel towards a partition at the end of the box.
When this rod or shaft has been pushed forward a stage, the lever rises again, until the next notch is reached, when the same thing occurs, and the rod gets a little nearer to the partition, in which, immediately facing the point of the rod, is a circular hole corresponding in circumference to the rod itself, so that ultimately the rod must pass through the hole into a recess between the partition and the end of the box.
The object of this will presently be seen. The two men, who are evidently skilled mechanics of a high class, are both young. Neither of them has yet numbered thirty years.
A third man is engaged in a totally different occupation. He is an old man, tall and thin, with a grave, professional face, small, keen eyes, and a high forehead. He is dressed in a long, dark blouse, and wears a black silk skull-cap. He has a square table before him in the centre of the room; on it are retorts, crucibles, phials, mortars, and pestles.
In a retort, beneath which burns a spirit-lamp, he is compounding something from which most obnoxious vapours arise, but immediately above is a skylight, which is open to give egress to the fumes.
The man watches the retort anxiously and nervously, and every few minutes he plunges a small thermometer into the boiling liquid, and then, withdrawing it, reads by the light of an Argand lamp what the figures indicate. At last he suddenly extinguishes the flame of the spirit, utters a sigh of relief, and straightens his aching back. As he does so, one of the two young men turns towards him, and says:
‘Well, Professor, have you finished?’