Astronomical Images : Blagrave's 'Theoricke of the sunnes motion, with the kalender'

John Blagrave

Astronomical Images

<p style='text-align: justify;'>This table, the 'Theoricke of the sunnes motion, with the kalender', was to be placed on the back of the universal astrolabe described by John Blagrave in <i>The Mathematical Jewel</i> (1585). The table contained calendrical information including the dominical letter, prime and epact for each year from 1582 to 1609. Users could have consulted this table to answer many of the questions asked of printed almanacs, for example, the day upon which a given date would fall in a particular year. With this 'Theoricke', Blagrave allowed users of the Jewel to solve calendrical problems without understanding the theory underlying the drawing up of the calendar. In fact, questions could be answered simply by looking up figures in the way that Blagrave described. In this way, Blagrave ensured that his instrument retained the simplicity of the printed almanacs which were so popular among contemporaries. The placement of the table on the back of the instrument thus demonstrates the close link between books and instruments in the period. This table was just one of three alternatives that Blagrave suggested might be placed on the back of the instrument - the others being a table of astrological information, or a map of the northern part of the World, appropriate to the student of astrology and the gentleman traveller respectively. Blagrave did not include figures of these features, but did refer readers to other books from which they could copy the relevant information, again showing the link between books and instruments. Moreover, Blagrave's interest in combining as many functions as possible in one instrument was shared by many instrument-makers of the time. The Jewel is thus related to the astronomical compendia produced in the late sixteenth and early seventeenth centuries. You can find out more about astronomical compendia on the Whipple Museum's 'Explore' website: http://www.hps.cam.ac.uk/whipple/explore/astronomy/astronomicalcompendia/</p>