all presented in succession; the Russian sailors, the Spaniards, young Pablo, and little Nina, on whom the professor, evidently no lover of children, glared fiercely through his formidable spectacles. Isaac Hakkabut, after his introduction, begged to be allowed to ask one question.
"How soon may we hope to get back?" he inquired.
"Get back!" rejoined Rosette, sharply; "who talks of getting back? We have hardly started yet."
Seeing that the professor was inclined to get angry, Captain Servadac adroitly gave a new turn to the conversation by asking him whether he would gratify them by relating his own recent experiences. The astronomer seemed pleased with the proposal, and at once commenced a verbose and somewhat circumlocutory address, of which the following summary presents the main features.
The French Government, being desirous of verifying the measurements already made of the arc of the meridian of Paris appointed a scientific commission for that purpose. From that commission the name of Palmyrin Rosette was omitted, apparently for no other reason than his personal unpopularity. Furious at the slight, the professor resolved to set to work independently on his own account, and declaring that there were inaccuracies in the previous geodesic operations, he determined to re-examine the results of the last triangulation which had united Formentera to the Spanish coast by a triangle, one of the sides of which measured over a hundred miles, the very operation which had already been so successfully accomplished by Arago and Biot.
Accordingly, leaving Paris for the Balearic Isles, he placed his observatory on the highest point of Formentera, and accompanied as he was only by his servant, Joseph, led the life of a recluse. He secured the services of a former assistant and dispatched him to a high peak on the coast of Spain, where he had to superintend a helioscope, which, with the aid of a glass, could be read from Formentera. A few books and instruments, and two months' victuals, was all the baggage he took with him, except an excellent astronomical telescope, which was, indeed, almost part and parcel of himself, and with which he assiduously scanned the heavens, in the sanguine anticipation of making some discovery which would immortalize his name.
The task he had undertaken demanded the utmost patience. Night after night, in order to fix the apex of his triangle, he had to linger on the watch for the assistant's signal-light, but he did not forget that his predecessors, Arago and Biot, had had to wait sixty-one days for a similar purpose. What retarded the work was the dense fog which, as mentioned before, at that time enveloped not only that part of Europe, but almost the entire world.
Never failing to turn to the best advantage the few intervals when the mist lifted a little, the astronomer would at the same time cast an inquiring glance at the firmament, as he was greatly interested in the revision of the chart of the heavens, in the region contiguous to the constellation Gemini.
To the naked eye this constellation consists of only six stars, but through a telescope ten inches in diameter, as many as six thousand are visible. Rosette, however, did not possess a telescope of this magnitude, and was obliged to content himself with the good, but comparatively small, instrument he had.
On one of these occasions, whilst carefully gauging the recesses of Gemini, he espied a bright speck which was unregistered in the chart, and which at first he took for a small star that had escaped being entered in the catalogue. But the observation of a few separate nights soon made it manifest that the star was rapidly changing its position with regard to the adjacent stars, and the astronomer's heart began to leap at the thought that the renown of the discovery of a new planet would be associated with his name.
Redoubling his attention, he soon satisfied himself that what he saw was not a planet; the rapidity of its displacement rather forced him to the conjecture that it must be a comet, and this opinion was soon strengthened by the appearance of a coma, and subsequently confirmed, as the body approached the sun, by the development of a tail.
A comet! The discovery was fatal to all further progress in triangulation. However conscientiously the assistant on the Spanish coast might look to the kindling of the beacon, Rosette had not a glance to spare for that direction; he had no eyes except for the one object of his notice, no thought apart from that of one quarter of the firmament.
A comet! No time must be lost in calculating its elements.
Now, in order to calculate the elements of a comet, it is always deemed the safest mode of procedure to assume the orbit to be a parabola. Ordinarily, comets are conspicuous at their perihelia, as being their shortest distances from the sun, which is the focus of their orbit, and inasmuch as a parabola is nearly an ellipse, but with its axis indefinitely produced, for some short portion of its pathway the orbit may be indifferently considered either one or the other; and in this particular case the professor was right in adopting the supposition of its being parabolic.
Just as in a circle it is necessary to know three points to determine the circumference, so, in ascertaining the elements of a comet, three different positions must be observed before what astronomers call its "ephemeris" can be established.
But Professor Rosette did not content himself with three positions; taking advantage of every rift in the fog he made ten, twenty, thirty observations both in right ascension and in declination, and succeeded in working out with the most minute accuracy the five elements of the comet which was evidently advancing with astounding rapidity towards the earth.
These elements were:
1. The inclination of the plane of the cometary orbit to the plane of the ecliptic, an angle which is generally considerable; but in this case the planes were proved to coincide.
2. The position of the ascending node, or the point where the comet crossed the terrestrial orbit.
These two elements being obtained, the position in space of the comet's orbit was determined.
3. The direction of the axis major of the orbit, which was found by calculating the longitude of the comet's perihelion.
4. The perihelion distance from the sun, which settled the precise form of the parabola.
