Astronomical Constants. The mean obliquity of the ecliptic for the year 1898 is 230 271 8/1.96. Mean annual diminution, O. 46.

The present accepted value of the solar parallax is 81.81 at the earth's mean distance, which is 92,790,000 miles, with a probable error of about 75,000 miles more or less.

The eccentricity of the earth's orbit is 0.016771; we are therefore 3,112, 560 miles nearer to the sun at perihelion (January 1) than at aphelion (about July 1).

Length of the sidereal year, 365 days, 6 hours, 9 minutes, 9.6 seconds of mean time.

Length of the tropical year (from equinox to equinox), 365 days, 5 hours, 18 minutes, 46.07 seconds of mean time.

Mean distance from earth to moon, 238, 850 miles.
The length of a second's pendulum, that is, one which vibrates once in a second, in vacuo,

ASTRONOMICAL CONSTANTS- Continued, at any place whose latitude is l, is 39. 01254 +0.20827 sin: l inches. At New York it is 39.1013 inches.

The acceleration of gravity in one second of mean solar time is 32.086528 +0.171293 sinal feet. The half of this is the distance through which a body falls (in a vacuum) in one second.

The velocity of light is 186,330 miles per second.

Light requires 8 minutes and 18 seconds to pass from the sun to the earth when at its mean distance, as given above;

therefore, when we look at the sun we see him not where he actually is, but where he was about 8 minutes and 18 seconds ago; his true place is then always in advance of his apparent place.

Pole Star. MEAN TIME OF TRANSIT (AT NEW YORK) AND POLAR DISTANCE OF POLE STAR

A. M.

sin p

E, M.S.OI IH, M.S. OIH. M.8. OI! H.M.S.

H.M.S. O 1 11 ||H, M 8. O I II
A. M.
A. M.

P. M.

P. M. 16 41 35 1 14 16 4 49 11 1 14 11 9 40 44 1 14 8 19 43 3 1 13 53 10 37 16 1 13 41 8 39 71 13 89 116 9 24 1 14 14

1 14 9 2 1 39 1 14 0 12 3 46 1 13 49 9 57 55 1 13 38 7 59 41 1 13 29 911 593 16 1 14 13 1 3 93 50 1 14 7 1 29 17 1 13 57 11 20 32 P.M. 1 13 46 9 18 39 1 13 34 7 20 141 1 13 97

From June 16 to August 1 both the upper and lower transits take place during daylight. The azimuth at the time of greatest eastern or western elongation can be easily computed from the formula:

sin A =

cOS 1 where A denotes the azimuth, p the polar distance, I the latitude of the place.

DATE OF GREATEST ELONGATION. To find the time of greatest eastern or western elongation, let H denote the hour angle, and I and p as before, then we shall have

cos H= tan p tan l. And the hour angle in mean time is

Hm= Ho X 0-0664846. This quantity, Am, added to or subtracted from the time of transit given above, according to the elongation required, will give the mean time of the greatest elongation at any place whose north latitude is l.

Star Table.
FOR IDENTIFYING THE PRINCIPAL FIXED STARS

Upper. Lower.

Upper.

Lower. H. M. H. M.

0 1

H. M. H. M. aAndromeda..

N 28 31 1 18.0 +10 40.0 a Leonis (Regulus). N 12 28 + 8 40.1 +20 88.1 y Pegasi (Algenib) N 14 37 1 18.2 +10 44.8 a Virginis (pica). S 10 37 H+11 56,5 +23 54,6 eCassiopeiæ..

N 56 58 - 0 42.3 +11 15. 8 a Bootis (Arcturus). N 19 43 +12 47.5 + 0 45.5 Arietis N 22 59+ 0 40.0 +12 38.0 BUrsæ Minoris..

N 74 85 +13 27.5 + 1 25.5 8Persei (Algol).. N 40 34 + 1 39.9 +13 37.9 aCoronæ Borealis.. N 27 4 +13 49.7 + 1 47.7 a Tauri (Aldebaran) N 16 18 3 8.2 +15 6.2 aScorpi (Antares) $ 26 12 1+14 59.8 + 2 57.3 Agrigæ (Capella). N 45 54 3 47.1 +15 45.1 (Lyra (Vega)

N 38 41 +17 9.3 + 5 7.3 Orionis (Rigel). S 8 19 + 3 47.6 +1E 45.6 a Aquilae (Altair).

N 8 36 +18 21.4 + 6 19.4 Orionis (Betelguese). N 7 23 + 4 27.6 +16 25.6 aCygni (Deneb). N 44 55 +19 13.5 + 7 11.5 aCanis Majoris (Sirius). S 16 35 + 5 18.4 +17 16.4 aCephei

N 62 9 +19 61.5 + 7 49.5 Gerninurum (Castor) NJ 7 6 5.7 +18 3.7 | Aquarii

S 0 49 +20 85.8 + 8 33.8 BGeminorum (Pollux).. N 28 16 + 6 16.6 +18 14.6 a Piscis Aus.

S 30 10 +21 27.1 + 9 25.1 GCanis Minor........ N 529 + 6 11.6 +18 9.6 la Pegasi (Markab). N 14 39 + 34.7 + 9 32.7

To find the time of the star's transit add or substract, according to the sign, the numbers In the second column of figures to the date of the transit of the pole star given above. Thus, for a Andromedæ February 1st Lower Transit of Polar Star is 4 h. 34.9

m. A. M., to which add 10 h. 40 m. and we have 3 h. 14.9 m. P. M.; for December 1st, we find 7 h. 21.1 m. P, M., etc.

EXPLANATION. –The white spaces indicate the amount of moonlight each night. Thus, January 7,
February 6, etc., the time of full moon, when for two or three nights in succession moonlight lasts
all night;January 14, February 13, etc., when the moon rises at or near midnight or when the latter
half of the night has moonlight; January 22, February 20, etc., the time of new moon, when for two
a three nights there is no moonlight; January 29, February 28, etc., when the moon sets at or near
midnight, or when the former half of the night has moonlight.