"Many of the minstrels were conjurers. These entertainers probably reached their greatest popularity in the fourteenth century, when they were known as tregetours. Some of their tricks were generally attributed to an understanding between the performer and the devil, this view being held by James 1. Accordingly, the tregetours were frequently classed with magicians, sorcerers and witches.
They often travelled about in companies, and it is to be assumed that they carried with them the various contrivances necessary for the performance of tricks which did not depend on the most precious accomplishment of the conjurer, then as today -- sleight of hand.
In 'The Frankeleyns Tale' Chaucer descries some of the tricks. Among them were the appearance, in a hall, of water and a barge, a lion, flowers, a vine, a castle of lime and stone -- all of which vanished as mysteriously as they had appeared:
For ofte at festes have I wel herd seye,
That tregetours, with-inne an halle large,
Have maad come in a water and a barge,
And in the halle rowen up and doun.
Sometyme hath semed come a grim leoun;
And somtyme floures spring as in a mede;
Somtyme a vyne, and grapes whyte and rede;
Somtyme a castle, al of lyme and stoon;
And whan hem lyked, voyded it anoon.
Thus semed it to every mannes sighte.
He also tells how there appeared wild deer, some being slain by arrows and some killed by the hounds. Falconers were seen on the bank of a river, where the birds pursued herons and slew them. Knights jousted on a plain. The amazed spectator saw himself dancing with his lady:
Doun of his hors Aurelius lighte anon,
And forth with this magicien is he gon
Hoom to his hous, and made hem wel at ese.
Hem lakked no vitaille that mighte hem plese;
So wel arrayed hous as ther was oon
Aurelius in his lyf saugh never noon.
He shewed him, er he went to sopeer,
Forestes, parkes ful of wilde deer;
Ther saugh he hertes with hir hornes hye,
The gretteste that ever were seyn with ye.
He saugh of hem an hondred slayn with houndes.
And somme with arwes blede of bittre woundes.
He saugh, whan voided were thise wilde deer,
Thise fauconers upon a fair river,
That with hir haukes han the heron slayn.
Tho saugh he knightes justing in a playn;
And after this he dide him swich plesaunce,
The he him shewed his lady on a daunce,
On which him-self he daunced, as him thoughte.
And whan this maister, that this magik wroughte,
Saugh it was tyme, he clapped his handes two,
And farewel! al our revel was ago.
And yet remoeved they never out of the hous,
Whyl they saugh al this sighte merveillous.
These were undoubtedly magic lantern effects, yet the lantern itself is usually thought to have been invented by Athanasius Kircher in the middle of the seventeenth century. The explanation, however, is that in the fourteenth century there were glass lenses which gave good telescopic and microscopic effects."