This section is from the book "Letters On Demonology And Witchcraft", by Walter Scott. Also available from Amazon: Letters On Demonology & Witchcraft.
But it is not private life alone, or that tenor of thought which has been depressed into melancholy by gloomy anticipations respecting the future, which disposes the mind to midday fantasies, or to nightly apparitions—a state of eager anxiety, or excited exertion, is equally favourable to the indulgence of such supernatural communications. The anticipation of a dubious battle, with all the doubt and uncertainty of its event, and the conviction that it must involve his own fate, and that of his country, were powerful enough to conjure up to the anxious eye of Brutus the spectre of his murdered friend Caesar, respecting whose death he perhaps thought himself less justified than at the Ides of March, since, instead of having achieved the freedom of Rome, the event had only been the renewal of civil wars, and the issue might appear most likely to conclude in the total subjection of liberty. It is not miraculous, that the masculine spirit of Marcus Brutus, surrounded by darkness and solitude, distracted probably by recollection of the kindness and favour of the great individual whom he had put to death to avenge the wrongs of his country, though by the slaughter of his own friend, should at length place before his eyes in person the appearance which termed itself his Evil Genius, and promised again to meet him at Philippi. Brutus's own intentions, and his knowledge of the military art, had probably long since assured him that the decision of the civil war must take place at or near that place; and, allowing that his own imagination supplied that part of the dialogue with the spectre, there is nothing else which might not be fashioned in a vivid dream or a waking reverie, approaching, in absorbing and engrossing character, the usual matter of which dreams consist. That Brutus, well acquainted with the opinions of the Pla-tonists, should be disposed to receive without doubt the idea that he had seen a real apparition, and was not likely to scrutinize very minutely the supposed vision, may be naturally conceived; and it is also natural to think, that no one saw the figure but himself, his contemporaries were little disposed to examine the testimony of a man so eminent, by the strict rules of cross-examination and conflicting evidence, which they might have thought applicable to another person, and a less dignified occasion.
Even in the field of death, and amid the mortal tug of combat itself, strong belief has wrought the same wonder, which we have hitherto mentioned as occurring in solitude and amid darkness ; and those who were themselves on the verge of the world of spirits, or employed in despatching others to these gloomy regions, conceived they beheld the apparitions of those beings whom their national mythology associated with such scenes. In such moments of undecided battle, amid the violence, hurry, and confusion of ideas incident to the situation, the ancients supposed that they saw their deities, Castor and Pollux, fighting in the van for their encouragement; the heathen Scandinavian beheld the Choosers of the Slain ; and the Catholics were no less easily led to recognise the warlike Saint George or Saint James in the very front of the strife, showing them the way to conquest. Such apparitions, being generally visible to a multitude, have in all times been supported by the greatest strength of testimony. When the common feeling of danger, and the animating burst of enthusiasm, act on the feelings of many men at once, their minds hold a natural correspondence with each other, as is the case with stringed instruments tuned to the same pitch, of which, when one is played, the chords of the other vibrate in unison with the tones produced. If an artful or enthusiastic individual exclaims, in the heat of action, that he perceives an apparition of the romantic kind which has been intimated, his companions catch at the idea with emulation-, and most are willing to sacrifice the conviction of their own senses, rather than allow that they did not witness the same favourable emblem, from which all draw confidence and hope. One warrior catches the idea from another ; all are alike eager to acknowledge the present miracle, and the battle is won before the mistake is discovered. In such cases, the number of persons present, which would otherwise lead to detection of the fallacy, becomes the means of strengthening it.
Of this disposition, to see as much of the supernatural as is seen by others around, or, in other words, to trust to the eyes of others rather than to our own, we may take the liberty to quote two remarkable instances.
The first is from the Historia Verdadera of Don Bernal Dias del Castillo, one of the companions of the celebrated Cortez, in his Mexican conquest. After having given an account of a great victory over extreme odds, he mentions the report inserted in the contemporary Chronicle of Gomara, that Saint Iago had appeared on a white horse in van of the combat, and led on his beloved Spaniards to victory. It is very curious to observe the Castilian cavalier's internal conviction, that the rumour arose out of a mistake, the cause of which he explains from his own observation; whilst, at the same time, he does not venture to disown the miracle. The honest conquestador owns, that he himself did not see this animating vision; nay, that he beheld an individual cavalier, named Francisco de Morla, mounted on a chestnut horse, and righting strenuously in the very place where Saint James is said to have appeared. But instead of proceeding to draw the necessary inference, the devout conquestador exclaims, —"Sinner that I am, what am I that I should have beheld the blessed apostle! "
The other instance of the infectious character of superstition occurs in a Scottish book, and there can be little doubt that it refers, in its first origin, to some uncommon appearance of the aurora borealis, or the northern lights, which do not appear to have been seen in Scotland so frequently as to be accounted a common and familiar atmospherical phenomenon, until the beginning of the eighteenth century. The passage is striking and curious, for the narrator, Peter Walker, though an enthusiast, was a man of credit, and does not even affect to have seen the wonders, the reality of which he unscrupulously adopts on the testimony of others, to whose eyes he trusted rather than to his own. The conversion of the sceptical gentleman of whom he speaks is highly illustrative of popular credulity, carried away into enthusiasm, or into imposture, by the evidence of those around, and at once shows the imperfection of such a general testimony, and the ease with which it is procured, since the general excitement of the moment impels even the more cold-blooded and judicious persons present to catch up the ideas, and echo the exclamations, of the majority, who, from the first, had considered the heavenly phenomenon as a supernatural weapon-schaw, held for the purpose of a sign and warning of civil wars to come.
 
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