Astronomical Images : Full-page figure of the mater of Blagrave's Jewel

John Blagrave

Astronomical Images

<p style='text-align: justify;'>This image comes from John Blagrave's <i>The Mathematical Jewel </i>(1585). In this work, Blagrave drew on a long tradition of guides to the construction and use of astrolabes, referencing works by Gemma Frisius and Johann Stoeffler amongst others. The new instrument that Blagrave presented as the mathematical jewel was an astrolabe of his own devising which had the benefit that it could be used anywhere in the World without the need to substitute different plates according to the latitude. This was one of two full-page images included at the front of <i>The Mathematical Jewel</i>. These full-page images were printed on one side of the paper whilst the other side was left blank. This meant that the pages could be pasted onto another medium and cut out, without any information being lost from the other side of the page. In fact, Blagrave offered some instructions on how to do this in the pages of the book. In this image, we can see the mater of the jewel onto which celestial circles had already been projected. In the corners of the image, surrounding the mater, were depictions of personifications of astronomy, cosmography, navigation and geometry. Notably, instruments feature in each of these depictions, in line with Blagrave's concern for practical interests. These figures would have been excised by readers who intended to assemble a working circular instrument from the two full-page images. However, several copies survive in which these pages have been left intact. As with the full-page image of the rete included in <i>The Mathematical Jewel</i>, there were further details to be added to the mater by readers who wanted to make an instrument from the pages of the book. Again, Blagrave advised on such additions in the body of the text.</p>