DAY. 



bird's nest ; tills, in its wild state, has a 

 sleii-iv r, hard, brownish, fusiform root ; 

 the stem is two ftt-t high, upright, groov- 

 ed with alternate tranches, which are 

 long', commonly from six to ten inches; 

 tin-; have one leaf, excvpi the primary or 

 terminating one, which is nuked ; and 

 have a single umbel of flowers at top ; 

 the universal umbel has sometimes from 

 thirty to forty unequal rays ; the middle 

 rays being very short, the Outur ones a- 

 bovc an inch long: the flowers are white, 

 those in i lie <niddle tinged w'.'.h purple, 

 the si; ;ii<- I f.de, those in the circumfer- 

 ence, wli.i-h Hi:- irregular ami larger, are 

 frequently neuter, or have pistils only : 

 the fruit is spheroidal, composed of pla- 

 noconvex seeds, on the back of which are 

 four mt-mbranaceous narrow crests, pec- 

 tinated with linear, setaceous, innocuous, 

 fli -xi. ile teeth. The carrot is commonly 

 cultivated in gardens for the kitchen ; the 

 different varieties of it are, in some 

 places esteemed ; in London, the orange 

 carrot is preferred to all others. 



DAY. In common language, the day 

 is the interval of time which elapses from 

 the rising to the setting of the sun; the 

 night is the interval that the sun continues 

 below the horizon. The astronomical 

 day embraces the whole interval which 

 passes during a complete revolution of 

 the sun. It is the interval of time which 

 passes from twelve o'clock at noon till 

 the next succeeding noon. It begins 

 when the sun's centre is on the meridian 

 of that place. It is divided into twenty- 

 four hours, reckoning in a numerical suc- 

 cession from one to twenty-four: the first 

 twelve are sometimes distinguished by 

 the mark P. M. signifying post meridiem, 

 or afternoon; and the .latter twelve are 

 marked A.M. signifying ante meridiem, 

 or before noon. But astronomers gene- 

 rally reckon through the twenty-four 

 hours from noon to noon ; and what arc 

 by the civil or common way of reckoning 

 called morning hours, are by astronomers 

 reckoned in the succession from twelve, 

 or midnight, to twenty-four hours. Thus, 

 nine o'clock in the morning of February 

 14th, is by astronomers called February 

 the 13th, at 21 hours. An astronomical 

 day is somewhat greater than a complete 

 revolution of the heavens, which forms a 

 sideral day. For if the sun cross the 

 meridian at the same instant with a star, 

 the day following it will come to the me- 

 ridian somewhat later than the star, in 

 consequence of its motion eastward, 

 which causes it to leave the star ;. and af- 

 ter a whole yesr has elapsed, it will have 

 crossed the meridian just one time less 



than the star. A sideral day is less than 

 the solar day, for it is measured by 360; 

 whereas tn mean solar day is measured 

 by 36U 5V 8" nearly. 



If an astronomical day be = 1, then a 

 sideral day is = 0.997269722; or the 

 difference between the nu-aiun-s of a 

 mean solar day and a sideral day, i-i:. 

 59' 8", reduced to time, at the rate, of 

 24 hours to 36l>, gives 3' 56"; from 

 which we learn tht asiur, which was on 

 the meridian with the sun on one noon, 

 will return to that meridian, 3' 56", pre- 

 viously to the next noon : therefore, a 

 clock, which measures mean days by 24 

 hours, will give 2oh 56m 4*, for the length 

 of a sideral day. 



Astronomical or solar days, as they are 

 also called, are not equal. Two causes 

 conspire to produce their inequality, 

 namely, the unequal velocity of the sun 

 in his orbit, and the obliquity of the eclip- 

 tic. The effect of the first cause is sen- 

 sible. At the summer solstice, when the 

 sun's motion is slowest, the astronomical 

 day approaches nearer the sideral, than 

 at the winter solstice, when his motion is 

 most rapid. To conceive the effect of 

 the second cause it is necessaiy to recol- 

 lect, that the excess of the astronomical 

 day above the sideral is owing to the 

 motion of the sun referred to the equator. 

 The sun describes every day a small arch 

 of the ecliptic. Through the extremi- 

 ties of this an.h suppose two meridian 

 great circles drawn, the arc of the equa- 

 tor, which they intercept, is the sun's mo- 

 tion for that day referred to the equator; 

 and the time which that arc takes to pass 

 the meridian is equal to the excess of the 

 astronomical day above the sideral. See 

 TIMK, equation of. 



The nychthcmeron is divided into 

 twenty-four parts, called hours, which are 

 of two sorts, equal and unequal, or 

 temporary. 



Different nations begin their day at a 

 different hour : thus the Egyptians began 

 their day at midnight, from whom Hippo- 

 crates introduced that way of reckoning 

 into astronomy ; and Copernicus and 

 others have followed him : but the great- 

 est part of astronomers reckon the day 

 begun at noon, and so count 24 hours till 

 the noon of the next day ; and not twice 

 12, according to the vulgar computation. 

 The method of beginning the day at 

 midnight prevails also in Great Britain, 

 France, Spain, and most parts of Europe. 

 The Babylonians began their day at sun- 

 rising, reckoning the hour immediately 

 before its rising again the 24th hour of 



