92 POPULAR FALLACIES. 



that when either of these objects are in the horizon, a portion, at least, of the 

 space between the eye and them is occupied by a series of objects with the 

 magnitudes and relative positions of which we are familiar. We are, there- 

 fore, enabled to make some estimate of a portion of the space that intervenes 

 between the eye and the object. But when the object is in a more elevated 

 position in the firmament, no part of the intervening distance is thus spaced 

 out, and we are accustomed to consider the object nearer to the eye. It is for 

 this reason that the first impression produced upon the mind by a view of the 

 firmament is that of a flat, spherical vault, resting upon the circle of the hori- 

 zon, the higher parts being much nearer to us than its horizontal boundaries. 

 This universal impression will be readily acknowledged by every observer. 

 Yet that it is a mental and not an optical deception, is proved by showing that 

 the visual magnitudes when measured are the same for every object at all al- 

 titudes. . 



Conceding this, then, it will be asked how it explains the universal impres- 

 sion of the enormously large disk of the sun or moon when rising or setting, 

 the answer is, that when in or near the horizon the mind is impressed with the 

 idea that the distance of these objects is much greater than when in the 

 meridian, and that their apparent magnitude being the same, the real magni- 

 tude is judged to be greater in the same proportion as the distance is supposed 

 to be greater. Thus, if we are impressed with the notion that the sun seen in 

 the horizon is twice as distant as the sun seen in the meridian, we shall infer 

 its diameter to be twice as great, since it appears the same ; and if its diame- 

 ter is twice as great, its apparent superficial magnitude will be four times as 

 great. 



The operations of the judgment in such cases are so rapid, and the effect 

 of habit is such, that we are altogether unconscious of them. A thousand ex- 

 amples might be given of bodily actions and motions performed by the dictates 

 of the will, of which we retain no consciousness. It is difficult in the case we 

 have just explained, for minds unaccustomed to metaphysical inquiries, to sat- 

 isfy themselves of the validity of the explanations we have given. Yet, if it 

 be remembered that it is capable of unequivocal proof that the illusion is not 

 optical, and that, in fact, the apparent magnitude of the moon in the horizon 

 and the meridian are not different, it will easily follow that the error must be 

 mental, and the only explanation which has ever been given of it is that which 

 we have here offered. 



While referring to the subject of the appearance of the sun and moon at ri- 

 sing and setting, I may take the opportunity of noticing the oval form which 

 they present, the vertical diameter being shorter than the horizontal diameter. 

 This is not, as in the former case, an optical illusion ; it is an effect produced 

 by the power of the atmosphere to deflect the rays of light which are transmit- 

 ted through it. By this principle of refraction, all objects appear at a greater 

 altitude than that which they really have ; and this error of position increases 

 as they approach the horizon. In accordance with this principle, the upper 

 limb of the sun is less elevated than the lower limb, and, consequently, the 

 two limbs are brought nearer together than they would be if equally affected 

 by refraction. On the other hand, the extremities of the horizontal diameters 

 being equally affected, its length is not altered. Since, therefore, the vertical 

 diameter is shortened, and the horizontal diameter unaltered, the figure becomes 

 an oval. Strictly speaking, this is the case with the sun and moon in all parts 

 of the heavens except in the zenith ; but the effect is so slight that, except at 

 lo\v altitudes, it is not perceptible. 



The cause of the red color which the sun and moon have when near the 

 > horizon is, that the atmosphere through which the light passes, being generally 



