But what shall be the import of this prognostic, if (as must frequently hap- 

 pen) the horns of the crescent, during the same evening, be at one time well, 

 and at another ill defined ; at one time sharp and distinct, at another time blunl 

 and confused ? Are we then to infer contradictory propositions ? Shall the 

 prognostic be true for both or false for both ? Another prognostic of Aratus is, 

 that if on the fourth day the moon project no shadow, we are to expect bad 

 weather during the month. 



As we have already observed, the light of the moon, or rather the light of 

 the sun reflected from the moon, must in reality be the same, and would, in > 

 fact, always appear the same in like positions to an eye placed beyond the ^ 

 limits of our atmosphere. The presence or absence of shadow is merely an ; 

 indication of a certain intensity of light, having reference to the sensibility of 

 the human eye. That the moon in a certain phase should at one time produce, / 

 and at another time not produce a shadow, is, therefore, merely an indication that < 

 the atmosphere through which her light has passed is at one time more trans- 

 parent than another. Now as the pure atmosphere has always the same de- 

 gree of transparency, these varying effects can only proceed from the vapors 

 which are mixed with it ; and thus, as before, the moon in this case is only a 

 sign of a certain state of the air at a particular time, and in a particular direc- 

 tion. The fourth day of the moon is selected, because on that day, if the at- 

 mosphere be very free from vapors, the light of the crescent is just sufficient 

 to produce a shadow ; but if any considerable quantity of vapors be present in 

 the atmosphere, even though they should not constitute what is called a cloud, 

 they may impair its transparency so much as to deprive the faint light of the 

 lunar crescent of the power of producing a shadow. Thus, as in the former 

 case, the moon is here used as a meteorological instrument to ascertain the hu- 

 ) midity of the air, and that only in the western direction, at or after sunset ; so 

 | that when translated into its true meteorological language, this prognostic is 

 equivalent to that to which we have just adverted. 



Varro, as quoted by Pliny, gives the following meteorological maxim : Nas- 

 cens Luna si cornua superior obatro surget, pluvias decrescent da l >it ; si infenore, 

 ante plenilunium ; si in media nigritia illafuent, imbrem in plena. 



" If the new moon have its upper horn darkened, the declining moon will be 

 attended with rain ; if the new moon have its inferior horn darkened, there 

 will be rain before the full moon ; and if the middle of the crescent be dark- 

 ened, there will be rain at the full moon." 



The obscurity here mentioned must, like those already alluded to, be produced 

 by the atmospheric vapors, rendering the medium through which the crescent is 

 beheld imperfectly transparent. If two lines be conceived to be drawn from 

 the eye of the observer in the direction of the points of the horns, and an inter- 

 mediate line toward the middle of the crescent, it will be evident that these lines 

 will diverge from one another very slightly. Now the obscurity of either the 

 upper or lower horn, or of the middle, the other parts being clear, would only 

 indicate the presence of imperfectly transparent vapor in the direction of one 

 of these lines, from which the others are free. To what, then, will this prog- 

 ) nostic amount ? That if the highest of these lines happen to encounter, at any 

 point of the space which it traverses, a sufficient quantity of vaporous matter 

 to render the superior horn indistinct, rain may be expected toward the de- 

 cline of the moon ; if a like portion of vapor be found in the direction of the 

 middle Kne, from which the other two lines are free, rain may be expected at 

 the full of the moon ; and if the obscure vapor be in the direction of the line 

 to the lower horn, rain may be expected in the increase of the moon ! It is 

 presumed that the absurdity of all this is sufficiently glaring, but it will be ren- 

 dered more so if it be considered that, by the spectator changing his position 



