July had now arrived. During the month Gallia’s advance along its orbit would be reduced to 22,000,000 leagues, the distance from the sun at the end being 172,000,000 leagues, about four and a half times as great as the average distance of the earth from the sun. It was traveling now at about the same speed as the earth, which traverses the ecliptic at a rate of 21,000,000 leagues a month, or 28,800 leagues an hour.
In due time the 62d April, according to the revised Gallian calendar, dawned; and in punctual fulfillment of the professor’s appointment, a note was delivered to Servadac to say that he was ready, and hoped that day to commence operations for calculating the mass and density of his comet, as well as the force of gravity at its surface.
A point of far greater interest to Captain Servadac and his friends would have been to ascertain the nature of the substance of which the comet was composed, but they felt pledged to render the professor any aid they could in the researches upon which he had set his heart. Without delay, therefore, they assembled in the central hall, where they were soon joined by Rosette, who seemed to be in fairly good temper.
“Gentlemen,” he began, “I propose to-day to endeavor to complete our observations of the elements of my comet. Three matters of investigation are before us. First, the measure of gravity at its surface; this attractive force we know, by the increase of our own muscular force, must of course be considerably less than that at the surface of the earth. Secondly, its mass, that is, the quality of its matter. And thirdly, its density or quantity of matter in a unit of its volume. We will proceed, gentlemen, if you please, to weigh Gallia.”
Ben Zoof, who had just entered the hall, caught the professor’s last sentence, and without saying a word, went out again and was absent for some minutes. When he returned, he said, “If you want to weigh this comet of yours, I suppose you want a pair of scales; but I have been to look, and I cannot find a pair anywhere. And what’s more,” he added mischievously, “you won’t get them anywhere.”
A frown came over the professor’s countenance. Servadac saw it, and gave his orderly a sign that he should desist entirely from his bantering.
“I require, gentlemen,” resumed Rosette, “first of all to know by how much the weight of a kilogramme here differs from its weight upon the earth; the attraction, as we have said, being less, the weight will proportionately be less also.”
“Then an ordinary pair of scales, being under the influence of attraction, I suppose, would not answer your purpose,” submitted the lieutenant.
“And the very kilogramme weight you used would have become lighter,” put in the count, deferentially.
“Pray, gentlemen, do not interrupt me,” said the professor, authoritatively, as if ex cathedra. “I need no instruction on these points.”