DAY. 



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

 slender, hard, brownish, fusiform root ; 

 the stem is two feet high, upright, groov- 

 ed with alternate branches, which are 

 long, commonly from six to ten inches ; 

 they have one leaf, 'except the primary or 

 terminating one, which is naked ; 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 outer ones 

 above an inch long : the flowers are white, 

 those in the middle tinged with purple, 

 ihese are fVrtile, those in the circumfer- 

 ence, which are irregular and larger, are 

 frequently neuter, or have pistils only; 

 the fruit is spheroidal, composed of pla- 

 noconvex seeds, on the back of which are 

 four mernbranaceous narrow crests, pec- 

 tinated with linear, setaceous, innocuous, 

 flexible 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, reckoningina numerical succession 

 from one to twenty -four : the first twelve 

 are sometimes distinguished by the mark 

 P. M. signifying post meridiem, or after- 

 noon ; ami the latter twelve are marked 

 A. M. signifying ante meridiem, or before 

 noon. But astronomers generally reckon 

 through the twenty-four hours from noon 

 to noon ; and what are 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 as- 

 tronomers 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 meridian somewhat later 

 than the star, in consequence of its mo- 

 tion eastward, which causes it to leave 

 the star ; and after a whole year 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 mea- 

 sured by 3(50 ; whereas the mean solar 

 day is measured by 360 59' 8" nearly. 



If an astronomical day be = 1, then a 

 sideral day is = 0.997269722; or the 

 difference between the measures of a mean 

 solar day and a sideral day, viz. 59' 8", re- 

 duced to time, at the rate of 24 hours to 

 360, gives 3' 56" ; from which we learn 

 that a star, which was on the meridian 

 with the sun on one noon, will return 

 to that meridian, 3' 56", previously to the 

 next noon : therefore, a clock, which 

 measures mean days by 24 hours, will 

 give 23 h 56> 4 } f or the length of a side- 

 ral 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's solstice, when his motion 

 is most rapid. To conceive the effect of 

 the second cause, it is necessary to recol- 

 lect, that the excess of the astronomical 

 clay above the sideral is owing to the 

 motion of the sun referred to the equa- 

 tor. The sun describes every day a small 

 arch of the ecliptic. Through the extre- 

 m ities of this arch 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 

 TIME, equation of. 



The nychthemeron is divided into 

 twenty -four parts, called hours, which 

 are of two sorts, equal and unequal, or 

 temporary. 



Different nations bgin 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 



