Astronomical Images : Full-page figure of the rete 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 rete of the mathematical jewel, as well as a ruler and alidade. The alidade is shown with sights, although it is not clear how these could have been cut out and made to stand perpendicular to the rest of the arm, as would have been required. Furthermore, it is clear from the level of detail, particularly in the upper half of the rete, that cutting the figure out would have been a challenging task. As well as pasting the figure down and cutting it out, the reader who intended to make these plates into an instrument needed to fill in certain details that had been left out of the printed image; for example, filling in the signs of the zodiac. Again, Blagrave provided instructions for these insertions elsewhere in the book, so it was important that the text and image were used together.</p>

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