This is the text of a conference paper, written informally for spoken delivery. I had hoped to develop this piece further, but have not gone back to it and doubt that I will do so now - it needs more astrological expertise for comparative analysis than I can muster. Apart from adding a couple of references and doing some minor tidying, it is presented here as prepared in 1998. When I have obtained permission from the copyright holders, I’ll include scanned versions of the numbered slides that were part of the original presentation.

The astrological instruments of Thomas Hood

XVII International Scientific Instrument Symposium, Soro
July 1998

Stephen Johnston
Museum of the History of Science
University of Oxford

In this paper today I want to present you with a first account of some newly discovered instruments from 16th-century England. I stress at the outset that this is a preliminary report. I first saw these devices at the end of last year and have as yet had worryingly little time or opportunity to study their every detail. Nevertheless, as well as giving a summary account of their form, I also want to present at least one direction which a full interpretation will have to study, by investigating where these instruments fit within the career of their author.

New 16th-century instruments are not discovered every day. However, these are not items which I have winkled out of some long-lost private collection or laboriously dug up from an archaeological site or an Elizabethan wreck; rather, they were sitting in one of the world’s most prominent places of research, the British Library. The 1994 annual report of the British Library’s recent acquisitions includes the following entry:

Astronomical diagrams by Thomas Hood, Mathematician; c. 1597; Vellum, in oaken cases. (Add. MSS. 71494, 71495)

Having previously published on the topic of Thomas Hood and instruments [see: ‘Mathematical practitioners and instruments in Elizabethan England’, Annals of Science, 48 (1991), 319-344], I was naturally curious to have a look at these enigmatically titled astronomical diagrams. This is what I found:

1. Double spread 71495

Rather than mere small-scale diagrams, as I was expecting, here was a large and beautiful diptych of illuminated vellum, the wooden mounting measuring about 43cm square. (Actually this is not exactly what I found, because the movable pieces had been wrongly assembled. My thanks to Silke Ackermann not only for arranging the photography of these instruments but also for persuading the British Library’s Conservation Department to dismount and reassemble the instruments.)

2. Tulip astrolabe

On the left is an astrolabe, evidently intended principally for astrological purposes. It has a tulip rete with a very large number of fixed stars - about 190 - each marked with their planetary temperaments. (It is worth noting in passing that the choice of a tulip form of rete raises interesting questions about the sources that Hood had to hand.) This rete rotates over a ‘mater’ with lines of unequal hours which is also divided into the houses according to the method associated with Regiomontanus. The houses each have a Latin text describing their character and influence. There is no direct indication of the intended latitude of the instrument, but by measurement of the distance from the north horizon point to the pole, the instrument was meant for use in about 52° - slightly south of London.

3. Volvelle 71495

On the other face is an astrological volvelle, with an outer zodiac scale encompassing 12 circular scales which, with the help of a lost index rule, indicated facies (i.e. decans), termini, exaltations, domus, gaudia, casus et detrimentum (i.e. occasus in Mercator’s terminology), masculine and feminine degrees, lucidi and tenebrosi, puteales, azemini and augentes fortunam. These scales surround a further 7 concentric circles which correlate the parts of the body with the planets for each of the signs of the zodiac. Each sign then has a text describing its qualities, and next in the sequence is a circular table indicating the planetary rulers of the hours of the days of the week. Finally, at the centre is a rotating volvelle disc which is graduated for the series of critical and other days in the course of an illness.

4. 71494 astrolabe

Nor was this all to be found. There was not just one of these double panels but two, of which this is the astrolabe face. Both pairs came to the British Library from the same source, the Science Reference Library and they bear the stamps of its former incarnation as the Patent Office Library. Their prior provenance has not yet been established.

This second pair of instruments is functionally almost identical. Although the distribution of scales is rather different, almost all the same features are present. The only substantial difference is that in this case the astrological astrolabe has a simplified rete whose only celestial feature is the ecliptic. This pair of instruments therefore perhaps represents a cheaper option; the tulip rete being a deluxe optional extra.

The omission of most of the rete detail allowed for a rearrangement of the material. Rather than appearing on the astrological volvelle, the circular table of the planetary rulers of the hours is here moved to the mater of the astrolabe, where the radiating spokes of the central circle of the rete serve as rotating indexes. The mater also has lines of unequal hours as well as the houses and their Latin explanatory texts, just as in the other astrolabe.

5. 71494 volvelle

Along with this simple astrolabe is another astrological volvelle, again with a disc for critical days at the centre surrounded by the same series of concentric astrological scales and texts stretching out to the outer zodiac scale. In this case the rotating index rule does survive to provide a handy identification of the sequence that we have already seen.

This summary outline is meant to give no more than a first flavour of the character of these instruments. In the remaining time I want to move out beyond the level of description, to consider how we might account for these instruments in a number of different histories.

It is really the last of these four that I want to focus on here, because it seems to me that these ‘paper’ instruments are most revealing on the personal level of Thomas Hood’s projects and mathematical activity. However it is worth at least reviewing each of my other three dimensions of interpretation.

Beginning with the history of astrology it seems safe to say that these instruments do not represent a major contribution to the art. The projection of the houses on the maters is standard for the period and the volvelles appear to be a compendious compilation into instrument form, rather than a deliberately innovative presentation.

6. Mercator disc

Much of the astrological information could have been borrowed wholesale from a source such as the Mercator astrological disc discussed by Steven Vanden Broeke [see now his ‘Dee, Mercator, and Louvain Instrument Making: An Undescribed Astrological Disc by Gerard Mercator (1551)’, Annals of Science, 58 (2001), 219-240]. Indeed, in his descriptions of the qualities of the signs of the zodiac, Hood has actually taken a portion of each of the texts directly from Mercator (or a common source).

7. Milan astrological astrolabe

Moreover, astrolabes specifically for astrological use were far from uncommon. This large example in the Pinacoteca Ambrosiana in Milan perhaps dates from the late 15th century and again features a simplified rete, along with a summary title for each of the houses.

So while Hood’s instruments will repay further study to place them precisely within their contemporary astrological context, I think it unlikely that they represent a unique or essential staging post in the narrative of the history of astrology.

What about the history of ‘paper’ instruments? Although they are collectively a fine example of this tradition, Thomas Hood was not treading novel territory here.

8. MHS Radcliffe MS 74 astrolabe

9. MHS Radcliffe MS 74 astrological volvelle

To take only an example from a manuscript of the mid-16th century in my own institution, we can see the contemporary currency of the practice of creating both finely drawn astrolabes and astrological volvelles in the medium of paper or vellum.

Elizabethan practical mathematics and instrument making was the third of my general headings which Hood’s instruments might illuminate. However, rather than broaching the topic now, I want to return to the Elizabethan significance of Hood’s work after considering the details of his own story.

10. Repeat slide of tulip astrolabe

11. Close up to show signature

And let’s begin with authorship. There can be no real doubt about the maker of these instruments. The tulip rete carries the signature ‘Thomas Hood fecit 1597’ and, although nothing else is signed, the instruments are all evidently by the same hand.

I want to suggest that these instruments have a very particular meaning in the context of Hood’s career, in which several points stand out:

12. West Indies ‘Thomas Hood made this platte 1592’

Charts serve as a neat way of underlining the temporal point, but also to demonstrate Hood’s skills as a draughtsman. We might typically tend to oppose the realm of university scholars and makers, but Hood was evidently more than just a lecturer, but a chart maker and a retailer of instruments.

From this review of Hood’s career, it is evident that at least the explicitly dated astrological instrument pair occupies a very particular moment, when he was seeking a licence to practice medicine in London. His failure to persuade the Royal College of Physicians of his Galenic orthodoxy meant that Hood had to turn his hand to his previous occupation as mathematical practitioner to survive - and Hood is quite explicit that this was his motivation for his publications and practice at the time. The creation of his astrological instruments falls into the same pattern of work.

13. Repeat Hood slide (71495 astrolabe)

These instruments were surely commissioned; certainly, the finesse and quality of their design, graduation and colouring strongly suggests that these were not Hood’s own personal working instruments but prestigious devices for sale or for presentation.

If they were indeed a commission, what was Hood’s own interest in the instruments? This is not a simple question to answer, and it is not immediately apparent that Hood even believed in or had confidence in astrology.

14. Celestial Globe in Plano (north)

This uncertainty is most vividly indicated by a book Hood had published in 1590, his The Use of the Celestial Globe in Plano, set foorth in two hemispheres. Accompanying the text were two planispheres on which Hood showed the stars with their planetary temperaments. Much of the work embodied in the 1597 tulip rete had already been compiled and accomplished in the star positions and astrological characters in his two planispheres of 1590. However, what is significant here is Hood’s attitude to the astrological information which he had provided on the fixed stars. In the dialogue between the master and the scholar which makes up the text of Hood’s 1590 text, the scholar asks the master:

Scholar: To what use is it to know the nature of the stars? [i.e. their planetary temperaments]
Master: To such questions I am loath to make answer: partly because I cannot justify that in experience which by reading I know and partly because I would not carry men’s minds away with these matters.

At the very least, Hood was cautious in public about astrological commitments. What therefore is the significance of his astrological instruments? Perhaps he had changed his mind between 1590 and 1597, and was now declaring his allegiance much more forcibly to the doctrines of astrology. Perhaps his manuscript instruments were private expressions of a practice he was reticent about in public. Perhaps. But neither of these possibilities seems to me entirely convincing. Given what we know about Hood’s rather parlous circumstances in 1597 - desperately seeking certification from the Royal College of Physicians and in the interim returning to mathematics for his livelihood - we might reasonably conclude that Hood sought any work of a mathematical kind to tide him over until he could devote himself to being a physician. And, in responding to the requests of patrons or clients, he was willing to produce work in which he may have had little or no faith or personal commitment.

Which brings us finally and briefly to what these manuscript instruments suggest about Elizabethan instruments and practical mathematics. Obviously, they add further grist to the mill of those who emphasise the extent to which astrology was integral to contemporary perceptions and practice of the mathematical arts and sciences in the 16th century. But they also suggest the fluidity of the boundaries of what constitutes an instrument. If we accept that mathematical instruments need not be made of brass, where do we draw the line? If Hood’s astrological devices are instruments, what of his sea charts? Should they also, as products of mathematical art, be identified as instruments?

I will not try to answer such questions now. However, I believe a full investigation will reveal more of the multiple significance of the astrological instruments of Thomas Hood, and I hope that what I have said today will whet your appetite for a larger account.