From Letters on Demonology and Witchcraft, Letter 1 (1830) by Sir Walter Scott
"Even in the field of death, and amid the mortal tug of combat itself, strong belief has wrought the same wonder… and those who were themselves on the verge of the world of spirits, or employed in dispatching 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 recognize 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 it is said is the case with stringed instruments tuned to the same pitch, of which, when one is played, the chords of the others are supposed to 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 favorable 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."
Scott’s work is available at Project Gutenburg, Google Books and the Electronic Text Center, University of Virginia Library.