Page:Popular Science Monthly Volume 22.djvu/586

570 them. In Europe the weather was generally bad. Good observations were made, however, at Potsdam, Prussia. The reports so far received from the southern hemisphere are most gratifying; and, whatever it may be with the stations yet to be heard from (chiefly near the Straits of Magellan), "enough is already secure to make it certain that we have observations sufficient in number and character to test the full value of the transit as a means of determining the solar parallax." It must be several years, however, before the observations can be fully reduced and published, and the exact results ascertained.

Work of the Dearborn Observatory.—The great equatorial of the Dearborn Observatory, Chicago, was employed during 1881, under the direction of Professor G. W. Hough, chiefly in the observation of the great comet of the year, the planet Jupiter, the satellites of Uranus, and difficult double stars. A drawing of the nucleus and envelope of the comet, showing the peculiar formation of the head and surrounding envelopes, was made on the 23d of June by Professor Colbert, who also first announced the distance of the comet from the earth. In attempting to reconcile the various phenomena alleged to have been seen on the disk of Jupiter, the greatest difficulty is found to exist in determining what is real and what is imaginary. Contemporaneous sketches by different persons, or even two by the same observer, show such marked discrepancies that they are of but little use in ascertaining suspected changes. The observations made here during the past three years confirm the statement that the changes on the disk of the planet are slow and gradual. The attempted observations on the inner satellites of Uranus were impeded by unfavorable night weather. About two hundred and fifty micrometer measurements of double stars were made, including nine measurements of the companions of Sirius. Sixty difficult double stars, not found in the catalogues, were discovered, including two quadruple systems and one naked-eye star, with a very minute companion. Mr. S. W. Burnham is preparing for publication a catalogue of one hundred and fifty-one double stars discovered at the observatory during the past three years; also, a compilation of all the star observations made by him during the same period, comprising about twenty-five hundred measurements. The observatory is open to members of the Chicago Astronomical Society on Thursday evenings; and classes from the city high-schools and elsewhere are occasionally admitted.

The Poles of Extreme Cold.—There appear to be two districts on the northern hemisphere, widely separated from each other, in which the coldest places on the earth are to be found. One is in Northeastern Siberia, the other in the American Arctic Archipelago. The particular points within these regions, that have the property of being colder than all surrounding points, may be called the poles of extreme cold. Their geographical situation is not precisely ascertained, because a sufficient number of observations have not been made, but enough is known to make it safe to conclude that the Asiatic pole is north of Yakutsk, and the American pole northwest of the Parry Islands, toward Eastern Siberia. The Asiatic pole is upon the mainland, the American pole in a sea studded with islands; and from this the two regions derive distinct climatic characters. Near the Siberian pole, which lies in the comparatively low latitude of from 60° to 70°, the continental climate is exhibited in an extremely cold winter and a warm summer, while the more maritime climate of the American pole, which lies between 65° and 68° of latitude, is expressed in a relatively milder winter and cooler summer. Yakutsk has hitherto been considered the coldest place on the earth, it having a mean temperature in January of -45°. Colder places have since been found that have a mean temperature for January as low as -55°. They are situated in about latitude 67° north, near Werkojansk, in Siberia. The cold-pole is located here from November till March; it then moves in April and May toward the northwest into the Arctic Ocean, between the mouth of the Obi and Nova Zembla, and afterward returns to Werkojansk. Werkojansk is the only place that lies within the isotherm of -40° during November, December, January, and February, or for four