determined to erect a great astronomical institution. He found most of the labor of fitting up the observatory yet to be done. He was given, as temporary quarters, with poor provisions for his work, a bastion on the Rhine called the Old Zoll.
With irrepressible industry he composed his beautiful work, the New Uranometry, or charts of the stars visible to the naked eye in central Europe, with their true magnitudes taken immediately from the sky. Taking up the field, hitherto but little worked, of the variable stars, he adopted the methods of Herschel, improving the notation. He expressed all the differences in light by numbers, and thereby opened the possibility of investigating phenomena which no one before him had subjected to calculation. Beginning in December, 1838, with observations of Mira Ceti, he included Algol in February, 1840, β Lyræ and other stars in the summer of the same year, and, with these, telescopic stars. At the same time he tried to excite interest in the subject in other quarters, at first with limited, afterward with increasing success; and in a short time this branch of our knowledge of the fixed stars assumed a new form. The discovery in 1843 of the decrease in Algol's period led to more thorough researches on the changes of the periods and their laws. Closer examinations of the older observations were brought in, and much that had been almost lost was looked up and collected. The observations were continued for many years, and it was not till 1859 that Argelander, without giving up his interest in the work, ceased to prosecute it actively, when his eyes were becoming weak, and when the general participation of others in it had satisfied him that it would be carried on.
The New Uranometry had originated, not only in the desire to present an enumeration of the stars, to clear the charts of errors of position and designation, and to furnish observers with the naked eye Avith a good atlas for orientation, but also out of the conviction of the importance of leaving to posterity a good representation of the relative magnitudes of the brighter fixed stars, in order to make the real secular variations in brightness distinguishable from fancied ones. The dissertation, De fide UranometricB Bayeri, is a contribution in this direction, and has the great merit of setting out in the right light the true principles from which Bayer had allowed himself to be led in the construction of his charts. Argelander's methods of observation in this field are summarized in an essay in Schumacher's Jahrbuch for 1844, from which many who have interested themselves in this line have drawn their instructions. The same work contains the first general summary of our knowledge of the subject from Argelander's hand, an important revision of which is found in Humboldt's Cosmos. This treatise also bespeaks many other phe-
