The daily morning journal and courier., 1900-04-05


 driving-Wheel of about 200o pounds
 and was so powerful that turning the telescope affected it more than does the hour-hand of an ordinary clock the 1 mechanism within it's case
 1 The final test of the whole adjustment
 consisted in noting whether stars once
 brought into the telescopic field of view 1 could be maintained there automatically 1 by means of the clock, This object
 having been attained successfully. the ] instrument stood ready to be used in
 the routine business of the observatory.
 Before leaving the subject of telescope mountings, we must mention tho giant | instrument now in course of oonstruc-
 tion at Paris. and which is to be fin-
 ished in time for this years exposition. It is intended to have it set LID for actual use, so that visitors will be able
 to examine personally what can be seen with the largest telescope the
 world has ever known. There has been for many years sort of quiet inter- ! national competition in the matter ot astronomical instruments. Americans have every reason to take pride in the l fact that this country has always pos sessed the instrument of greatest | power. Perhaps the most famous of all | telescope lens-makers was the late AL | win Clark of Cambridgeport, Mass. He and his son furnished large lenses for the United States and Russian govern ments, for the Lick observatory, and finally for the great 40-inch telescope of the Yerkes observatory, near Chicago This last instrument is at present the 1n in, avic hI1f if will ha eS11r passed by the new one at Paris,
 The most important consideratum in telescopes in great light gathering power; and this depends simply on the size of the lens. The Yerkes glass, which is 40 inches across, possesses this power in very high degree. But, in- stead of 40, the Paris instrument is to be a little mere than 49 inches in size, which will make the light-gatherng power one-half as large again as that of the Chicago glass.
 But the most remarkable peculiarity at Paris is the proposed extraordinary length of the entire instrument. The tube is to be 19S feet long, or more than three times the length of any existing telescope. There are certain optical reasons in favor of these huge propor- tions. It is impossible for human hands to grind an absolutely perfect lens, and the remaining unavoidable imperfec- tiona have the least harmful effect if things are arranged so as to put the ob- servers eye as far as possible from the other end of the tube. The limit upon length has been Imposed hitherto by the purely mechanical difficulty of handling instruments of excessive weight. It is simply matter of me- chanical engineering.
 At Paris the objection will be avoided rather than overcome. It is proposed to make the tube immovable, and to mount it horizontally in fixed position. Then, in order to observe different parts of the sky, mirror will be placed in front of the telescope, and the sky ex- amined by reflection only. This mirror will then be provided with polar axis and clockwork so as to accomplish the same result as if tha telescope itself could move. The only fault in this ar rangement is it's increased complexity The mirror is an additional glass to grind and polish, and If they do not sue ceed in making it perfectly flat, slight distortions will be produced In the star images under observation. Astronomers are looking forward with much con- cern to the scientific success or failure of this great instrument. Let us hope that it will help to throw light upon some of the many astronomical prob lems awaiting solution in the new cen- tury.
 The following predictions give the po- sitions of the principal cancellations at p. nl., April 15, 1900; but they will al- so be found approximately correct at The same hour throughout the month";
 Orion is now about to set in the west ern horizon. Auriga, the charioteer, and twin-starred Gemini hang above him, nearly half way up to the zenith. The great dog-star Sirius,is down near the horizon, but the little dog-star. Procyon is still about halfway up to the zenith a little south of west Leo is on the meridian, about due south, up nearly three-fifths of the distance, from hori- zon to zenith It shows sickle-shaped figure with the open blade turned to the right and the handle straight up and down. In that handle glows the gem star, Regulus. Virgo is in the south east, one-third of the way up to the zenith. The Great Bear is overhead, just above the pole.
 One of the planets, Venus, is evening star and just after sunset will be found in the western sky, about halfway up to the zenith. It is near the Pleiades | group, especially in tke early part of the month. The closest approach will | be on April 4. Mercury is morning star in the latter half of the month. There | will be good opportunity to see it on the 21st, near the eastern horizon just | before sunrise. Jupiter and Saturn are stars, and just before sunrise are little west of south, above the horizon from one-fifth to one-quarter of | the distance up to the zenith On April 20 rather unimportant shower of meteors is expected. The moon will pass close to Venus on the 2d, to Jupiter on the 18th, and to Saturn on the 20th. Jacobi in Boston Transcript.
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