Time Reckoning: Time Tables

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In his first section on time reckoning, Michael copied out several different tables. These tables put a wealth of information at his disposal.

Generic calendar

The first item Michael copied is a generic annual calendar, good for any year (95-102b). The calendar's most important feature is a list of saints and martyrs to be honored on different days of the year. It includes celestial information as well: the number of hours of night and day at different times of year (for a roughly Venetian latitude); the point at which the sun enters a new sign of the zodiac each month; and notes pertaining to the visibility of the moon. Many days are also flagged with stars or crosses. The stars mark the rising of stars in the sky thought to affect weather, while the crosses identify "perilous" days on which Michael thought it unwise to begin anything new, like a voyage.

Bloodletting lunare

Bloodletting was a common medical procedure in the Middle Ages. Michael's manuscript includes notes on the likely results of bloodletting on specific days of the month (102b-103a): on the 2nd, "You will be feverish"; on the 13th, "You will get fat from eating little"; and, ominously, on the 23rd, "There will be presentiments of sudden death."

A beautiful diagram accompanies Michael's notes on bloodletting (page icon 103b). It indicates which signs of the zodiac govern which parts of the body. The idea behind the diagram is that blood is a liquid and therefore affected by the moon, just like the tides. When the moon was in a given sign, there would be a "high tide" of blood in the corresponding part of the body. Bloodletting was to be avoided at that time.

Signs of the zodiac

One of the highlights of Michael's manuscript follows his medical foray into astrology: an exquisitely illustrated rendering of the signs of the zodiac (103a-109b; page icon 103b, 107a, 108b). Michael describes the dominant element (earth, air, fire, or water) and quality (hot, wet, cold, or dry) for each sign and names the planet that rules it. He provides a general sketch of the character of the person born under each sign, along with brief medical advice and other information. His text reflects the "soft astrology" of the Middle Ages which admitted the influence of the heavens on Earth, but did not involve horoscopes or the creation of detailed natal or predictive charts.

Moon tables

After further notes on star risings and unlucky days, Michael includes three tables relating to the moon. The first gives the date of Easter for every year from 1401 to 1500 (129b)—the annual date of Easter being determined in relation to the first full moon after the spring equinox.

Michael's second table (page icon 130b) was intended to let the reader determine what sign the moon was in on any day of the month (useful for bloodletting, for example). This table, however, is badly corrupted; Michael made quite a few mistakes copying it.

Michael's third and longest table is a Table of Solomon, named after the biblical King Solomon, who was renowned throughout the Middle Ages for his wisdom (131b-135a; page icon 131b). The table provides the day, date, and time of the new moon for every month of every year from 1435 to 1530—extremely valuable information for a mariner. Like the first table, this one also gives the annual date of Easter. Each row of the table includes a special number that could be used to determine the weekday of any day in a given year. (Learn more about the Table of Solomon.)

Computus manualis

Michael's second section on time reckoning (185a-190a) covers a number of topics related to the computus manualis. Computus was the medieval Latin name given to computations involving the ecclesiastical calendar, particularly those determining the date of Easter. Computus manualis was the method of carrying out these calculations by counting on one's fingers, instead of looking them up in tables.

In this section, Michael's subject matter includes calculations of the lunar epact, which is the calculated age of the moon on a given day of the year; from this number, the moon's age on all other days can be found. He also offers a method for checking the accuracy of his Table of Solomon, as well as a method for calculating the hours of daylight on any given day.

Michael refers explicitly to hand diagrams in three of the topics he explores. One drawing was for the method of calculating the annual lunar epact. A second was for calculating what we would now call the solar concurrent (the number of the weekday of March 24 in a given year) which could be used to find the weekday of any calendar day in a year. The last concerned the date of "Hebrew Passover," preceding Easter.

Unfortunately, although he left space for them, Michael never did draw the hand diagrams into his manuscript. He did include drawings of hand calculations in the later manuscript he wrote that bears the name of Pietro di Versi; he also wrote in that manuscript that the methods for calculatiing the rising of the moon were made "by the hand of Michael of Rhodes in 1444."

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