We give on the preceding page an engraving of this astrolabe from a photograph, which presents a sufficiently accurate outline of the instrument. The plate was originally made to illustrate Mr. Marshall's article in the Magazine of American History, and we are indebted to the courtesy of the proprietors of the Magazine, Messrs. A. S. Barnes and Company of New York, for its use for our present purpose. The astrolabe, as an instrument for taking the altitude of the stars or the sun, had long been in use. Thomas Blundevile, who wrote in 1622, says he had seen three kinds, and that the astrolabe of Stofflerus had then been in use a hundred years. It had been improved by Gemma Frisius. Mr. Blagrave had likewise improved upon the last-mentioned, and his instrument was at that time in general use in England. The astrolabe continued to be employed in Great Britain in taking altitudes for more than a century subsequent to this, certainly till Hadley's Quadrant was invented, which was first announced in 1731. The astrolabes which had the broadest disks were more exact, as they were projected on a larger scale, but as they were easily jostled by the wind or the movement of the ship at sea, they could with difficulty be employed. But Mr. Blundevile informs us that "the Spaniards doe commonly make their astrolabes narrow and weighty, which for the most part are not much above five inches broad, and yet doe weigh at the least foure pound, & to that end the lower part is made a great deale thicker than the upper part towards the ring or handle." _Vide M. Blendeale his Exercises_, London, 1622, pp. 595, 597. This Spanish instrument, it will be observed, is very similar to that found on the Old Portage road, and the latter may have been of Spanish make. In order to take the latitude in Champlain's day, at least three distinct steps or processes were necessary, and the following directions might have been given. I. Let the astrolabe be suspended so that it shall hang plumb. Direct the index or diopter to the sun at noon, so that the same ray of light may shine through both holes in the two tablets or pinules on the diopter, and the diopter will point to the degree of the sun's meridian altitude indicated on the outer rim of the astrolabe. II. Ascertain the exact degree of the sun's declination for that day, by a table calculated for that purpose, which accompanies the astrolabe. III. Subtract the declination, so found, if it be northerly, from the meridian altitude; or if the declination be southerly, add the declination to the meridian altitude, and the result, subtracted from 90 deg., will give the latitude.