518 • MOONLIGHT. 



and its changes taught men the true nature of the moon, as an opaque 

 globe circling round the earth, and borrowing her light from the sun. They 

 perceived, first, that the moon was only fall when she was opposite the sun, 

 shining at her highest in the south at midnight when the sun was at his 

 lowest beneath the northern horizon. Before the time of full moon, they 

 saAv that more or less of the moon's disk was illuminated as he was nearer 

 or farther from the position opposite the sun, the illuminated side being 

 towards the west — that is, towards the sun ; while after full moon the same 

 law was perceived in the amount of light, the illuminated side being still 

 towards the sun, that is, towards the east. They could not fail to observe 

 the horned moon sometimes in the day time, with her horns turned directly 

 from the sun, and showing as plainly, by her aspect, whence her light was 

 derived, as does any terrestrial ball lit up either by a lamp or by the sun. 

 The explanation they gave was the explanation still given by astrono- 

 mers. Let us briefly consider it. In doing so I i^rojiose to modify the ordi- 

 nary text-book illustration which has always seemed to me ingeniously 

 calculated (with its double set of diversely illuminated moons around the 

 earth) to make a simple subject obscure. 



Fig. 1. 



In Fig. 1, let E represent the earth one half in darknefss, the other half 

 illuminated by the rays of the sun, S, which should be supposed placed at 

 a much greater distance to the left, in fact about five yards away from E. 

 To preserve the right proportions, also, the sun ought to be much smaller 

 and the earth a mere point. I mention this to prevent the reader from 

 adopting erroneous ideas as to the size of these bodies. In reality it is 

 quite impossible to show, in such figures, the true proportions of the 

 heavenly bodies and their distances. JSText let M, M\ JVr, M^, etc., represent 

 the moon in different portions along the circuit around the earth at E. 



Now, it is clear that when the moon is at M\ her illuminated face is 

 turned from the earth, E. She, therefore, cannot be seen, and accordingly, 

 in Fig, 2, t-he is presented as a black disk at 1 to correspond with her in- 

 visibility when she is at M^ She passes on to J\P, and now from E a part 

 of her illuminated half can be seen towards the sun, which would be to- 

 wards the right if we can imagine an ej-e at B looking towards Ml Her 



