Cyrus Harding gazed for some time at this splendid constellation, which has at its summit and at its base two stars of the first magnitude, at its left arm a star of the second, and at its right arm a star of the third magnitude.

Then, after some minutes thought—

"Herbert," he asked of the lad, "is not this the 15th of April?"

"Yes, captain," replied Herbert.

"Well, if I am not mistaken, to-morrow will be one of the four days in the year in which the real time is identical with average time; that is to say, my boy, that to-morrow, to within some seconds, the sun will pass the meridian just at midday by the clocks. If the weather is fine I think that I shall obtain the longitude of the island with an approximation of some degrees."

"Without instruments, without sextant?" asked Gideon Spilett.

"Yes," replied the engineer. "Also, since the night is clear, I will try, this very evening, to obtain our latitude by calculating the height of the Southern Cross, that is, from the southern pole above the horizon. You understand, my friends, that before undertaking the work of installation in earnest it is not enough to have found out that this land is an island; we must, as nearly as possible, know at what distance it is situated, either from the American continent or Australia, or from the principal archipelagoes of the Pacific."

"In fact," said the reporter, "instead of building a house it would be more important to build a boat, if by chance we are not more than a hundred miles from an inhabited coast."

"That is why," returned Harding, "I am going to try this evening to calculate the latitude of Lincoln Island, and to-morrow, at midday, I will try to calculate the longitude."

If the engineer had possessed a sextant, an apparatus with which the angular d