SCIENCE. 
295 
before the red spot had began 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 I 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 seventh magnitude star. Our clock refractor, ol ap- 
erture of 8X oches, was used with power of 50. 
Latitude of Observatory, 44 0 27' 40.77". Longitude 
from Washington, ih. 4m. 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 
New Moon 1 9 48 ] First Quarter. 
Full Moon 15 22 28 Last Quarter.. 
New Moon 30 20 48 I 
D. H. I\I. 
8 1 30 
24 1 49 
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 ol greatest 
obscuration. In addition to these solar eclipses there 
will be a total eclipse of the moon December 15-16, invi- 
s'ble 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 0 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, Saturn crossing the meridian at 7h. 
53m., a few minutes after Jupiier. The brilliant mark- 
ings upon Jupiter’s belt have Deen attracting universal 
attention. 
Uranus, crossing the meridian about 5 o’clock in the 
morning, is in R. A. iih. im. 26s. deck + 7° 6.2'. 
Neptitne 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 0 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 least 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. Martin is engaged in polishing the object gla<-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 below 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 an 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. 
