The Lesser Key of Solomon, Crowley/Mathers edition, 1904:
This is the Form of the Magical Triangle, into the which Solomon did command the Evil Spirits. It is to be made at 2 feet distance from the Magical Circle and it is 3 feet across. Note that this triangle is to be placed toward that quarter whereunto the Spirit belongeth. And the base of the triangle is to be nearest unto the Circle, the apex pointing in the direction of the quarter of the Spirit. Observe thou also the Moon in thy working, as aforesaid, etc.