Astronomical Instruments

Tycho Brahe’s seminal work on astronomical instruments, his Astronomicae instaurata mechanica, first published at Wandsbek in 1598, was collected by Worth in the 1602 Nuremberg edition:

 

Tycho Brahe, Astronomicae instaurata mechanica (Nuremberg, 1602), title page.

The Armillary Sphere

‘Since… the use of these instruments [the altazimuth type] for astronomical purposes essentially requires trigonometrical calculations which are not easily comprehensible to everybody and particularly cumbersome to certain people who shun labour, certain other appliances have been invented, with the aid of which the latitudes and longitudes of the stars, the two quantities particularly required, can be found with little inconvenience and without troublesome calculations. I find that two of these in particular were used by the ancients. One is the so-called armillary instrument that was used by Hipparchus and Ptolemy, who gave it its name. The other is called the torquetum, an instrument which in my opinion was invented by the Arabians or the Chaldaeans, and used by them.’

Tycho Brahe on the differences between his instruments and earlier ones, cited in Bennett (1987), p. 25.

Ptolemy outlines his various instruments in his Almagest but undoubtedly the most complex was the armillary sphere. In the following woodcut of a zodiac armillary in Brahe’s Astronomia instaurata mechanica we can see that the polar axis is marked by the letters CD and the axis of the ecliptic as IK. The outermost rings are set in the meridian while the inner rings move to set the polar axis and establish the ecliptic co-ordinates:

 

Tycho Brahe, Astronomicae instaurata mechanica (Nuremberg, 1602), C3v.

This zodiac armillary was built for Brahe’s observatory at Uraniborg in 1581. It would be accompanied four years later by his equatorial armillary which he housed at his secondary observatory at Stjerneborg. Both these instruments would have allowed Brahe to check the stellar positions as regards right ascension and declination. Brahe regarded his equatorial armillary at Stjerneborg as the high point of his armillary sphere production: initially his armillary spheres had very heavy objects but as he realised that their weight was introducing errors into his data he made them successively lighter by reducing the number of rings. The increasing precision of his instruments, and in particular his equatorial armillary, allowed him to investigate in more detail the problem of refraction.

As Chapman argues (1995), what was crucial to the success of Brahe and his successors was the development in the early modern period of more refined methods of subdivision of degrees. Brahe was obsessed with assuring accuracy in every possible way: he substituted a ‘peg and slit’ system on the sighting arms of his measuring instruments instead of the cruder ‘pinnule system’ which had previously prevailed because he realised that sighting through the pinnule sights had been producing errors in observation. At his observatory at Uraniborg Brahe was constantly attempting to perfect his instruments. Perhaps his most successful – and certainly most celebrated instrument – was his mural quadrant.

Brahe’s Mural Quadrant

 

Tycho Brahe, Astronomicae instaurata mechanica (Nuremberg, 1602), Sig. a6v.

Brahe built his famous mural quadrant at Uraniborg in 1582 and it played an important role in his subsequent observations of declinations of stars below 45o. However, as Gingerich and Voelkel point out in a seminal article on Brahe (1998), the mural quadrant could only be used for meridian observations and it was for this reason, when he contemplated the search for the parallax of Mars, that he turned his attention to the trigonal sextant. Brahe gives detailed description of all these instruments (and many more) in his Astronomia instaurata mechanica and was anxious to describe their use since the accuracy of his observations (his chief claim to fame) was completely dependent on them. He made it clear that he did not depend on just one instrument per observation but would combine the use of a number in order to get the closest value he could. Wesley (1978), using a computer programme and Brahe’s own observational logs for the period 1583-1590 to check the accuracy of Brahe’s instruments, concentrated on eight different types of instrument used by him: his mural quadrant which was 6.5. feet in radius; his revolving wooden quadrant, 5 feet in radius; his revolving steel quadrant, 6 feet in radius; his small brass azimuthal quadrant, 2 feet in radius; his portable brass azimuthal quadrant, 2 feet in radius; his astronomical sextant; 5 feet in radius; two equatorial armillary spheres, 5 feet in diameter and the large equatorial armillary sphere, 9 feet in diameter. He came to the conclusion that Brahe’s instruments were very accurate indeed, to within 30″ to 50″ – and what divergences there were could be ascribed to misreading of the scales rather than any inherent problem with the instrument itself. Of all the instruments the large mural quadrant scored the highest, undoubtedly because, being fixed to the wall, it was much more stable than the other instruments, despite their impressive size.

Johannes Hevelius’s Machinae Coelestis (Danzig, 1673)

In many ways Hevelius’s Machinae Coelestis and Brahe’s Astronomia instaurata mechanica are similar works. Both authors were anxious to underline the accuracy of their observations by giving details of the construction and use of their instruments. Indeed many of the instruments in Brahe’s work are commented on in that of Hevelius also. One of Brahe’s earliest interactions with astronomical instruments had been with the ‘Great Quadrant’ measuring at 14 cubits radius at Augsburg and here we see Hevelius using a quadrant:

 

Johannes Hevelius, Machinae Coelestis (Danzig, 1673), Fig. D.

And in Fig H he depicts how he uses weights to control it. The engraving of this image is so clear that the figures on the base plate are visible:

Johannes Hevelius, Machinae Coelestis (Danzig, 1673), Fig. H.

Worth’s copy of Jan Luyts Astronomia insitutio (Utrecht, 1692) contains a diagram on the use of the quadrant from a different perspective:

 

Jan Luyts, Astronomia institution (Utrecht, 1692), p. 32.

From Hevelius’s illustrations it is clear that his instruments were conceived on a grand scale – just like those of Brahe. Equally there were strong similarities in the sextants both men used: in the following illustration we see Hevelius’s plate of a sextant:

Johannes Hevelius, Machinae Coelestis (Danzig, 1673), Fig. B.

However, Hevelius’s use of sextants did differ from Tycho’s for he improved on them by adding a tracking screw to mark the position of stars he was observing. The attraction of a sextant was its versatility and mobility – a fact that came in handy when Brahe was forced into exile in the last years of his life.

The Telescope

The chief difference between Brahe’s Astronomia instaurata mechanica and Hevelius’s works on astronomical instrumentation lay not in their function but in their scope. Brahe died a few years before the arrival of the telescope on the astronomical scene; Hevelius became one of its chief exponents.

Hevelius did not concern himself with exactly who had invented the telescope. Unlike Worth’s copy of Pierre Borel’s historical investigation of the subject which accorded the invention to two German-Dutch lens makers, Hans Lipperhey and Zacharius Jansen, Hevelius concentrated on the fruits of the invention and the mechanics involved in building a telescope.

 

Pierre Borel, De vero Telescopii inventore (The Hague, 1655), title page.

The Machinae Coelestis though specifically about astronomical instruments, was not Hevelius’s first foray into the subject: in his Selenographia (Danzig, 1647), a work also collected by Worth, Hevelius had gone to some trouble to outline the process of observation before launching into a description of the solar system and more particularly the Moon. In his Selenographia he paid particular attention to the construction of lenses, concentrating on lenses with spherical curvature, the properties of Venetian glass and the methods of fitting them into telescopes. As Winkler and Van Helden point out (2003), Hevelius was careful to link his practical and theoretical discussions, bringing into play optical theory, the configuration of lenses and problems of mounting telescopes. The last was no easy matter: in two of the thumbnail illustrations at the foot of this page we can see Hevelius’s depictions of a telescope in both an urban and rural environment. There are two things of interest here: first, the length of the telescope – Hevelius was using very large telescopes indeed. Van Helden (1974) relates that ‘from about 1645 to 1650 the length of good telescopes increased from 6-8 feet to 10-15 feet, while magnifications increased about 30 to 40 diameters’ and there were further increases in lengths after 1650. Hevelius’s Machinae Coelestis was published in 1673 when the length of many telescopes had increased up to 50 feet. He himself went far beyond this, building telescopes of up to 140 feet long. Secondly, what is striking about both scenes is their communal nature. As Van Helden reminds us (1994), observation was not always undertaken alone but might be conducted in a social setting in order to lend greater authority to the act.

Despite his work on detailing the construction and use of telescopes Hevelius was still very old school when it came to his method of observation. His instruments were undoubtedly the best that money could buy and his own observations had proved incredibly influential but his adherence to naked eye observation was soon to be superseded by the use of telescopic sights on traditional instruments. This had been the core of his dispute with Robert Hooke who was a vociferous advocate of the use of telescopic sights. Hevelius’s distaste for telescopic sights on quadrants and sextants seems strange given the fact that his Machinae Coelestis was seen by many as a treatise on the importance of the telescope. And indeed he was a strong advocate of the telescope – but as an instrument on its own, used in conjunction with more traditional instruments certainly but not attached to them. In the Machinae Coelestis Hevelius provides us with plates of seventeen separate instruments, among which are a number of telescopes. In the following plate we see a group of telescopes together with a quadrant in the background and at the foot of this web page in the gallery, on Hevelius rooftop observatory we can see a combination of telescopes, quadrants and sextants together.

Johannes Hevelius, Machinae Coelestis (Danzig, 1673), Fig. X.

Despite Hevelius’s disquisition on telescopes and his use of them he was against the amalgamation of telescopic sights to older instruments, advocating instead the importance of naked eye observation. One reason for this was because he himself could produce wonderful observations using quadrants and sextants in the traditional manner but as Hooke pointed out in his debate with Hevelius in the 1670s, not everybody was gifted with Hevelius’s phenomenal eyesight and telescopic sights therefore gave better results. English authors such as John Flamsteed and Edmond Halley agreed – and indeed the latter visited Hevelius in a bid to convert him to telescopic sights (to no avail). It is therefore of interest that Worth’s collection includes nearly all the works of Hevelius and hardly anything by Halley, nothing by Flamsteed, and only a 1705 collected works of Hooke and his Micrographia (London, 1667). (Another gap in Worth’s collection is the absence of any of the works of Cassini – though it should be said that one of his treatises is included in a 1723 compilation).

Worth as a Fellow of the Royal Society would have been very much aware of the Hooke-Halley-Hevelius debate on astronomical instruments but there was also a reason closer to home why he would have taken an interest in this quarrel about telescopic sights: William Molyneux, 1656-1698, a founding member of the short-lived Dublin Philosophical Society, had played a role in the debate. In a series of letters and reports in the Papers of the Dublin Philosophical Society Molyneux outlined the bones of the debate. Writing to Francis Aston on 12 November, 1685 Molyneux considered the implications of the debate for Hevelius:

‘One great design of Hevelius in this book seems to be the vindicating of his instruments and observations performed by them from the defects, on account of their plain sights, imputed to them by some celebrated astronomers, but especially by the ingenious Mr Hook in his Animadversions on the first part of his Mach. Caelestis [sic]. This is manifest from the preface prefixed to this Annus climactericus and from several letters adjoined to the end of the book, as well as from the history of Mnst. Hevelius’s and Mr Halley’s congress inserted in the body of the book. And indeed, ‘tis not wonder he should be so mightily concerned in this particular, for hereupon the price of his astronomical labours for his whole life (excepting only his Selenography) does wholly depend, and if this foundation be once shaken, how mightily are all his endeavours disappointed. The vast charges he had been at for astronomy are all to no more purpose than Ticho’s and that splendid apparatus of instruments described by him so advantageously in his first Mach. Caelestis, becomes mere lumber. But surely th[at] were an event highly deplorable, not only to the party himself immediately concerned but to the whole republica literaria, for it may deservedly be said of the noble and incomparable Hevelius, that he alone by his own labours and charges had done more towards the advancement of astronomy than the joint forces of all ages, both before and coeval with him, forasmuch as yet appears.’

Hoppen (2008), The Papers of the Dublin Philosophical Society.

Molyneux was personally interested in the construction of telescopes and sundials and in 1686 produced a book called the Sciothericum telescopium (Dublin, 1686) – a work which is in the Worth Library. The work is concerned with the technical possibilities of adding telescopic sights to a sun dial and Molyneux was clearly fond of the production, declaring to the Dublin Philosophical Society that his new invention had ‘improved the art of dialling, before lame and imperfect, to that accurateness that he can determine the time of day to two seconds, and by a most ingenious application of telescopic sights to it had made it so universal that by any known star he can determine most exactly the time also of the night.’ He seems to have be alone in his enthusiasm – certainly noted astronomers such as his friend John Flamsteed the Astronomer Royal, to whom he had demonstrated the use of the instrument, were less enthralled by its possibilities, pointing out its inaccuracies. In the following illustration we see Molyneux’s foldout plate of his new invention:

 

Sciothericum telescopium (Dublin, 1686), foldout plate.

The Astrolabe

The only work in the Worth Library which examines the use of an astrolabe is ‘The Treatise on the Astrolabe’ written by Geoffrey Chaucer for his son Lewis and incorporated into the 1532 edition of Chaucer’s collected works bought by John Worth in Dublin in 1684. The text is a brief and very simple introduction to the use of an astrolabe and was initially intended as a description for children. However, it incorporated technical details which assured it a wider readership and, as Eagleton (2007) points out, many subsequent astrolabes were based on his designs. The Worth copy contains none of the illustrations present in some of the manuscript copies of the text – and in fact there are very few illustrations of astrolabes in the Worth library. Undoubtedly the reason for this was because the astrolabe had long been superseded by more modern instruments by the time Edward Worth was collecting his scientific books. Tycho Brahe in his fascinating study makes no mention of them. For more on astrolabes see The an Online Resource

In fact the only illustration of an astrolabe found to date in the Worth Library is an incidental one – in an engraving of an astronomer in his study surrounded by his tools where we can glimpse an astrolabe on the wall:

 

Jean Picard, Voyage d’Uranibourg, ou, 
Observations astronomique faites en Dannemarck (Paris, 1680), heading ornament.

Selected Reading

Bennett, J. A. (1987). The Divided Circle. A History of Instruments for Astronomy, Navigation and Surveying. Oxford: Phaidon.
Bennet, J. (2003). ‘Presidential Address: Knowing and Doing in the Sixteenth Century: What were Instruments For?’, The British Journal for the History of Science 36, no. 2, 129-150.
Chapman, A. (1995). Dividing the Circle. The Development of Critical Angular Measurement in Astronomy 1500-1850 Chichester: John Wiley and Sons.
Eagleton, C. (2007). ‘Chaucer’s own astrolabe: Text, Image and Object’, Studies in History and Philosophy of Science 38, 303-326.
Gingerich, O. and Voelkel, J. R. (1998). ‘Tycho Brahe’s Copernican Campaign’, Journal for the History of Astronomy XXIX, 1-34.
Hoppen, K. T. (ed.) (2008) Papers of the Dublin Philosophical Society 1683- 1709 (Dublin: Irish Manuscript Commission), 2 vols.
Jambeck, T. J. and Jambeck, K. K. (1974). ‘Chaucer’s Treatise on the Astrolabe: A Handbook for the Medieval Child’, Children’s Literature 3, 117-122.
Lorch, R. (2005). ‘The literature of the astrolabe to 1450’ in K. Van Cleempoel. Astrolabes at Greenwich. A Catalogue of the Astrolabes in the National Maritime Museum, Greenwich. Oxford: Oxford University Press, pp 23-30.
O’Hara, J. G. (2004). ‘William Molyneux (1656-1698), experimental philosopher and constitutional writer, ODNB.
Proctor, D. (2005). ‘The Construction and Use of the Astrolabe’ in K. Van Cleempoel. Astrolabes at Greenwich. A Catalogue of the Astrolabes in the National Maritime Museum, Greenwich. Oxford: Oxford University Press, pp 15-22.
Simms, J. G. (1982). William Molyneux of Dublin. Edited by P. H. Kelly. Dublin: Irish Academic Press.
Van Helden, A. (1974). ‘The Telescope in the Seventeenth Century’, Isis 65, no. 1, 38-58.
Van Helden, A. (1994). ‘Telescopes and Authority from Galileo to Cassini’, Osiris 2nd Series, 9, 8-29.
Wesley, W. G. (1978). ‘The Accuracy of Tycho Brahe’s Instruments’, Journal for the History of Astronomy IX, 42-53.
Winkler, M. G. and Van Helden, A. (2003). ‘Johannes Hevelius and the visual language of astronomy’, in J. V. Field and F. A. J. L. James (eds.) Renaissance and Revolution. Humanists, scholars, craftsmen and natural philosophers in early modern Europe. Cambridge: Cambridge University Press, pp. 97-115.