'Canones Horoptri', ten rules for finding the time of sunrise and sunset, the Golden Number, the position of the sun in the Zodiac, etc.: the treatise itself, not any instrument, is called a Horoptrum. This appears to be the copy dedicated and presented to king Henry viii, the dedication being dated Jan. 1. 152 8/9 and bearing the author's name 'Nicolaus Cratzerus', the well-known horologer. He explains that it was originally composed for 'Guilielmus Tylar, King's chamberlain (cubicularius): but the present volume does not contain all that is promised in the list of contents. The handwriting, as I am assured by Mr. P. S. Allen, is that of Peter Meghen, Colet's scribe.