He could talk of nothing but stars and constellations. He ought to have lived in a telescope. As an observer be had not his rival; his patience was inexhaustible; he could watch for months for a cosmical phenomenon. He had a specialty of his own, too; he had studied luminous meteors and shooting stars, and his discoveries in this branch of astronomical science were considerable. When ever minute observations or exact measurements and definitions were required, Thomas Black was chosen for the service; for his clearness of sight was something remarkable. The power of observation is not given to everyone, and it will not therefore be surprising that the Greenwich astronomer should have been chosen for the mission we are about to describe, which involved results so interesting for selenographic science.

We know that during a total eclipse of the sun the moon is surrounded by a luminous corona. But what is the origin of this corona? Is it a real substance? or is it only an effect of the diffraction of the sun's rays near the moon? This is a question which science has hitherto been unable to answer.

As early as 1706 this luminous halo was scientifically described. The corona was minutely examined during the total eclipse of 1715 by Lonville and Halley, by Maraldi in 1724, by Antonio de'Ulloa in 1778, and by Bonditch and Ferrer in 1806; but their theories were so contradictory that no definite conclusion could be arrived at. During the total eclipse of 1842, learned men of all nations-Airy, Arago, Keytal, Langier, Mauvais, Otto, Struve, Petit, Baily, &c.-endeavoured to solve the mystery of the origin of the phenomenon; but in spite of all their efforts, "the disagreement," says Arago, "of the observations taken in different places by skilful astronomers of one and the same eclipse, have involved the question in fresh obscurity, so that it is now impossible to come to any certain conclusion as to the cause of the phenomenon." Since this was written, other total eclipses have been studied with no better results.

Yet the solution of the question is of such vast importance to selenographic science that no price would be too great to pay for it. A fresh opportunity was now about to occur to study the much-discussed corona. A total eclipse of the sun-total, at least, for the extreme north of America, for Spain and North Africa-was to take place on July 18th, 1860. It was arranged between the astronomers of different countries that simultaneous observations should be taken at the various points of the zone where the eclipse would be total. Thomas Black was chosen for the expedition to North America, and was now much in the same situation as the English astronomers who were transported to Norway and Sweden on the occasion of the eclipse of 1851.

It will readily be imagined that Thomas Black seized with avidity the opportunity offered him of studying this luminous halo. He was also to examine into the nature of the red prominences which appear on different parts of the edge of the terrestrial satellite when the totality of the eclipse has commenced; and should he be able satisfactorily to establish their origin, he would be entitled to the applause of the learned men of all Europe.

Thomas Black eagerly prepared for his journey. He obtained urgent letters of recommendation to the principal agents of the Hudson's Bay Company. He ascertained that an expedition was to go to the extreme north of the continent to found a new fort. It was an opportunity not to be lost; so he set out, crossed the Atlantic, landed at New York, traversed the lakes to the Red River settlement, and pressed on from fort to fort in a sledge, under the escort of a courier of the Company; in spite of the severity of the winter, braving all the dangers of a journey across the Arctic regions, and arriving at Fort Reliance on the 19th March in the condition we have described.

Such was the explanation given by the astronomer to Captain Craventy. He at once placed himself entirely at Mr Black's service, but could not refrain from inquiring why he had been in such a great hurry to arrive, when the eclipse was not to take place until the following year, 1860?

"But, Captain," replied the astronomer, "I heard that the Company was sending an expedition along the northern coast of America, and I did not wish to miss the departure of Lieutenant Hobson."

"Mr Black," replied the Captain, "if the Lieutenant had already started, I should have felt it my duty to accompany you myself to the shores of the Polar Sea."

And with fresh assurances of his willingness to serve him, the Captain again bade his new guest welcome to Fort Reliance.