It is impossible to study the preceding phenomena without being impressed with the conviction, that nature is full of the marvellous, and that the progress of science and the diffusion of knowledge are alone capable of dispelling the fears which her wonders must necessarily excite even in enlightened minds. When a spectre haunts the couch of the sick, or follows the susceptible vision of the invalid, a consciousness of indisposition divests the apparition of much of its terror, while its invisibility to surrounding friends soon stamps it with the impress of a false perception. The spectres of the conjuror, too, however skilfully they may be raised, quickly lose their supernatural character; and even the most ignorant beholder regards the modern magician as but an ordinary man, who borrows from the sciences the best working implements of his art. But when, in the midst of solitude, and in situations where the mind is undisturbed by sublunary cares, we see our own image delineated in the air, and mimicking in gigantic perspective the tiny movements of humanity;--when we see troops in military array performing their evolutions on the very face of an almost inaccessible precipice--when, in the eye of day, a mountain seems to become transparent, and exhibits on one side of it a castle which we know to exist only on the other; when distant objects, concealed by the roundness of the earth, and beyond the cognisance of the telescope, are actually transferred over the intervening convexity and presented in distinct and magnified outline to our accurate examination;--when such varied and striking phantasms are seen also by all around us, and therefore appear in the character of real phenomena of nature, our impressions of supernatural agency can only be removed by a distinct and satisfactory knowledge of the causes which gave them birth. It is only within the last forty years that science has brought these atmospherical spectres within the circle of her dominion; and not only are all their phenomena susceptible of distinct explanation, but we can even reproduce them on a small scale with the simplest elements of our optical apparatus. [Illustration: _Fig. 35._]