SCIENCE. 



295 



before the red spot had begun to appear at the east 

 limb. It has kept up its rapid motion with probably no 

 particular change in appearance. 



From the observed transits of November 22 and De- 

 cember 2, its rotation period is 9h. 50m. 19.4s. It 

 gains 5 m. 18 s. on the red spot at each rotation, or 12 

 m. 48 s. per day. Should this spot continue permanent 

 for one month longer it will have made the circuit of 

 Jupiter and again be seen passing the great red spot on 

 the night of January 4. On that night the white and red 

 spots will transit together at 11 h. 39 m. 



E. E. Barnard. 



Nashville, Tenn., December 6. 



To the Editor of Science : 



Last night 1 viewed Swift's Comet, and found that the 

 Ephemeris computed by Mr. Upton, of the Naval Observ- 

 atory, Washington, answered quite closely, and was from 

 note book as follows : 



swift's comet. 

 Northfield, Minn., Mean Time, ioh. 52m. 

 R. A. 3h. 32m. 

 Dec. 51° 28 . 

 The Comet was well seen, having about the brightness 

 of a seventti magnitude star. Our clock refractor, ot ap- 

 erture of Z)i nches, was used with power of 50. 



Latitude of Observatory, 44 27' 40.77". Longitude 

 from Washington, ih. 4T1. 23.02s., which has been re- 

 cently determined telegraphically by aid officers of the 

 Coast Survey. Respectfully yours, 



Wm. W. Payne. 

 Northfield, Minn., Dec. 2, 1880. 



Astronomical Memoranda.— (Approximately com- 

 puted for Washington, D. C, December 13, 1880) : 



H. M. S. 



Sidereal time of Mean Noon 17 31 2 



Equation of time. 5 J 4 



mean noon following apparent time. 

 The Moon's phases for the month are : 



D. H. M. I D- H. M. 



New Moon 1 9 48 ! First Quarter 8 1 30 



Full Moon 15 22 28 ] Last Quarter 24 1 49 



New Moon 30 20 48 



We have the somewhat unusual occurrence of two 

 new moons in the month, and both of them cause partial 

 eclipses of the sun. The eclipse of the first was invisible 

 in the United States ; that on the morning of the thirty- 

 first is partially visible. The sun rises eclipsed and re- 

 mains so until a little after nine o'clock, nearly three- 

 quarters of its disk being covered at the time of greatest 

 obscuration. In addition to these solar eclipses there 

 will be a total eclipse of the moon December 15-16, invi- 

 sible in the United States, but visible in Central Asia. 



Mercury may be seen during the week rising about an 

 hour before the sun, and 5 farther north. 



Venus now crosses the meridian nearly three hours 

 after the sun, and is steadily growing brighter as she 

 approaches the earth. 



Mars has reached a sufficiently great distance from 

 the sun to be readily seen about an hour before sunrise 

 close to the eastern horizon. It is 2° farther north than 

 the sun, and is easily recognized by its red color. Mars 

 and Mercury are in conjunction on the 23d. 



Jupiter and Saturn have changed but little their re- 

 lative positions, Satu-n crossing the meridian at 7I1. 

 53m., a few minutes after Jupiier. The brilliant mark- 

 ings upon Jupiter's belt have oeen attracting universal 

 attention. 



Uranus, crossing the meridian about 5 o'clock in the 

 morning, is in R. A. nh. im. 26s. decl. + 7° 6.2'. 



Neptune rises about midnight and reaches the meri- 

 dian at 9 o'clock, at an altitude of 48 . 



The Great Nebula in Orion situated around the small 

 quadruple star Orionis (the central one of three stars 

 which form Orion's sword-hilt) will be found of great 

 interest to all possessing good telescopes. It rises at 6 

 P. M., and is just visible as a nebulous mass to the 

 naked eye. 



In a communication to the Colorado Academy of Sci- 

 ence, Prof. George Davidson, of the U. S. Coast and 

 Geodetic Survey, has placed upon record the somewhat 

 unusual occurrence of a naked eye observation of one of 

 Jupiter's satellites. The station was Monticello, over- 

 looking the Sacramento Valley, 3,125 feet above the sea 

 level. Jupiter, at an elevation of 8°, was slowly rising 

 through a sn.oky atmosphere, without the lease radia- 

 tion. The third satellite was noticed first by Prof. 

 Davidson, below the disk and somewhat to the left, and 

 was readily seen by four other persons, when attention 

 was called to the phenomenon. Its position was after- 

 wards confirmed by the aid of a field-glass. The satel- 

 lite remained visible for about twenty minutes, and was 

 finally rendered invisible by the moonlight. On subse- 

 quent nights with much clearer sky and no moon, no satel- 

 lites could be made out with certainty by the unassisted 

 eye. 



There is a very ingenius instrument in use at the 

 Greenwich Observatory to record automatically the dura- 

 tion of sunshine through the day. It consists of a glass 

 globe hung within a hemispherical cup of slightly greater 

 diameter. This cup is lined with a strip of paper covered 

 with stencil ink. While the sun is shining, the globe, 

 which is entirely exposed upon the roof, acts as a burn- 

 ing glass, and causes a continuous line to be made upon 

 the paper. This line will be broken, however, as often as 

 the sun's light is obscured by clouds, and thus a deter- 

 mination of the amount of sunshine for the day will be 

 obtained. 



M. Manin is engaged in polishing the object gla c s of 

 the large refracting telescope now building at the Paris 

 Observatory. The diameter of this exceptional lens is 

 73 centimetres, and its weight 200 kilograms. The qual- 

 ity of the glass having proved defective, it has already 

 broken twice, and the operation is now being made on 

 the third casting. —Nature. 



We learn from Nature that Prof. Bell, together with 

 M. Janssen has been making some experiments at Meu- 

 don, upon the application of the photophone to the study 

 of sounds which occur on the sun's surface. " A solar 

 image 0.65m. in diameter " was explored with the selen- 

 ium cylinder, but no very marked results were obtained. 



Schmidt calls the attention of observers to a sharp 

 black spot in the northern part of Jupiter's belt, which 

 gives a time of rotation=9h. 55m., while the heavy white 

 clouds in the middle of the belt give 9I1. 50m. 



W. C. W. 



Washington, D. C, December 8, 1880. 



A new optical milk test has been invented by Messrs. 

 Mittelstrap, Magdeburg. A given quantity of milk, and 

 also of water is examined by looking through different 

 thicknesses until opacity is reached. The vessel holding 

 the liquid has a glass bottom, and in its cover a vertical 

 graduated tube in a slide, with glass closing its lower end. 

 Light is thrown up fr ,m r<dow by means of an oblique 

 mirror, or from a direct source. The tube (through which 

 one looks) is moved in the slide until the light disappears, 

 and at this point the scale is read off. Professor Maercker 

 has made experiments with this apparatus, and states it to 

 be very accurate ; the greatest difference between the deter- 

 mination of fat in milk, with it, and by chemical analysis, 

 being ail average of 0.1 per cent. The usefulness of the 

 instrument applies only to fresh milk, and for skim-milk a 

 special tube is prepared. 



