The Controversy over the use of Telescopic Sights. Hevelius observes the Skies with Edmond Halley Two Months Before his Observatory is Lost to Fire

Hevelius, Johannes (1611-1687)

Johannis Hevelii Annus climactericus, sive Rerum uranicarum observationum annus quadragesimus nonus; exhibens diversas occultationes, tam planetarum, quàm fixarum post editam machinam coelestem; nec non plurimas altitudines meridianas solis, ac distantias planetarum, fixarumq́ue, eo anno, quousque divinaconcessit benignitas, impetratas: cum amicorum nonnullorum epistolis, ad rem istam spectantibus: & continuatione historiae novæ stellæ in collo Ceti, ut & annotationum rerum coelestium ...

Danzig: Sumptibus auctoris, typis D.F. Rhetii, 1685


Folio: 34.8 x 22.5 cm. [6] lvs. 24, 196 pp. Collation: )( 6, )(4, )()(4, )()()(4, A-Z4, AA6. With engraved title page vignette and 7 (1 double-page) engraved plates.


Bound in 18th c. half calf and marbled boards with very slight wear. Spine with citron morocco label, gilt. A nice copy with a few early marginal paper repairs (no loss.) The final two leaves of the table with repaired tears, the second of these with a small natural paper flaw costing a few letters. Complete with the seven plates, engraved by Hevelius himself.

“Annus Climactericus” was the last of Hevelius’ works published in the author’s lifetime. The book comprises observations of the planets, sun, moon, and fixed stars, many of which were made alongside the English astronomer Edmond Halley. The observations were made from 8 January until 25 September 1679, subsequent to the publication of the second volume of Hevelius’ “Machina Coelestis”, almost the entire press run of which was lost in the fire that destroyed Hevelius’ observatory on 26 September 1679. Hevelius also included new observations of the binary star Omicron Ceti, which Hevelius had been observing for 25 years (and which he had named “Mira”) and grappled with the problem of its changing size and color. In addition, the book includes Hevelius’ observations of the Great Comet of 1680 (illustrated by a magnificent double-page plate, engraved by Hevelius), the total lunar eclipse of February 1682, the comet of 1682, the solar eclipse of July 1684 (each also accompanied by a plate “Observator Sculpsit.”), observations of several Great Conjunctions, etc.

There are also numerous letters to and from members of the Royal Society of England: Henry Oldenburg, John Wallis, John Flamsteed, Nehemiah Grew, and Halley, as well as several European astronomers, among them Ismaël Boulliau. The letters deal primarily with Hevelius’ feud with Robert Hooke over the merits of the use of telescopic sights for celestial observation (vide infra.)

The “Climactic Year” to which the title of the book refers is 1679, the year in which Hevelius published his “Machinae Coelestis pars Posterior”, which comprised 49 years worth of Hevelius’ celestial observations; and the year in which his observatory burned to the ground. In the introduction, Hevelius gives his own account of the fire that consumed not only the observatory building itself, but also Hevelius’ instruments (“tam astronomicis quam opticis”), his library, his printing press and print making workshop, and the irreplaceable stock of his self-published works. He also describes the psychological and emotional toll that the fire took on him, and thanks God that at last, his spirit (“in cineribus hactenus fere supultum”) was revived by the arrival of the Great Comet of 1680, and that he was able to make new observations.

Hevelius, Hooke, and Halley: The Controversy over Open-Sight Instruments vs. Telescopic Observation

The “Annus Climactericus” is of great importance in the history of science, marking as it does the climax of a contentious debate between Hevelius, who argued that his “open-sighted” instruments (employing fore- and near-sights but no lenses or cross-hairs) were more accurate than those fitted with telescopic sights (micrometers with telescopic lenses and cross-hairs), and Robert Hooke, who argued against that position.

Hooke and Hevelius had been arguing (politely) over the relative merits of both kinds of instruments since the 1660s but matters came to a head in 1673 with the publication of Hevelius’ “Machinae Coelestis Pars Prior”, in which Hevelius forcefully enumerated the limitations of telescopic sights, and Hooke’s critique of the book, in which he wrote that readings taken with Hevelius’ instruments could not be more accurate than ½ minute of arc. He mocked Hevelius’ instruments (which Hooke asserted were no better than the antiquated ones used by Tycho almost a century earlier), his observations, and methods. Moreover, he asserted that Hevelius was not only providing the scientific community with incorrect data, but was impeding scientific progress itself.

Hevelius responded with a letter to Henry Oldenburg in which he asserted that his observations were in fact accurate to within 5 seconds of arc, that he had never seen data that proved Hooke’s assertions, and that he resented Hooke’s ad hominem attacks. Inevitably, the astronomer John Flamsteed was drawn into the controversy and, though he had great respect for Hevelius and voiced his disapproval of Hooke’s attacks, felt compelled to note some of the errors in Hevelius' observations. Hevelius responded and the two men carried on a correspondence in which they argued over the data, and during which Hevelius leveled charges of jealousy against Flamsteed, and voiced his conviction that Flamsteed and Hooke were now conspiring against him. Fortunately, the rift was eventually healed. Part of the correspondence is included in the “Annus Climactericus”.

1679: A Comparative Test:

The arrival at Danzig of Edmond Halley, who brought with him his portable 2 –foot quadrant fitted with telescopic sights, presented an opportunity to compare results obtained with both types of instruments. The two men made observations side-by-side from 26 May to 18 July 1679, using Halley’s instrument and Hevelius’ own quadrant, “with which he made regular observations of the Sun, the large sextant for angular distances between stars, planets, and the limbs of the Moon, and his 12-foot telescope for occultations.” Hevelius’ wife Elizabeth, Hevelius’ personal printer, and two other observers also participated.

Before Halley left Danzig, he wrote (at Hevelius’ request) what amounted to a testimonial to the accuracy of Hevelius’ open-sighted instruments. Halley wrote that he could testify “to the certainty of the instruments against all who would cast doubt on Hevelius’ observations. He had seen with his own eyes that not just occasional observations but many by different observers with the large sextant agreed incredibly well together and any discrepancies were very small, which he greatly admired.”(Cook, p. 100)

In the introduction to the “Annus Climactericus”, Hevelius excoriated Hooke and boasted that his calculations demolished Hooke’s assertions of the inferiority of Hevelius’ methods. The book was reviewed in the Philosophical Transactions of September-October 1685 by Hooke’s antagonist John Wallis, who censured Hooke for his behavior toward Hevelius and took pains to rehearse each of Hevelius’ criticism of Hooke and to summarize the 27 letters of support that Hevelius printed in the “Annus”. Hooke responded to Hevelius in February 1686 in an effort to vindicate himself and Hevelius, in turn, wrote that he would publish his long-awaited star catalog, “Uranographia” to furnish proof of the superiority of his methods, but Hevelius’ death the following year put an end to the dispute.

Postscript: Hevelius and Halley

Hevelius printed Halley’s positive assessment of the Danzig astronomer’s instruments and calculations in the “Annus Climactericus” (p. 101-102) and thereby drew Halley into the controversy with Hooke. Moreover, Hevelius misrepresented the reason for Halley’s visit, stating that he had invited Halley to Danzig (the visit was Halley’s own idea), that he had asked him to bring the telescopic quadrant (which Halley had actually brought with him to make observations of the southern constellations on St. Helena), and that Halley came to Danzig as an official representative of the Royal Society (of which Halley was not yet a member.)

This all irritated Halley, who, in order to extricate himself from the Hevelius-Hooke controversy, downplayed his original estimation of the accuracy of Hevelius’ calculations. Halley also realized that while attesting to the accuracy of Hevelius’ instruments, he seemed to side with Hevelius against Hooke, whose belief in the superiority of telescopic sights was in fact Halley’s own.

While he never attacked Hevelius, he put it forth that his earlier enthusiasm had been in part motivated by a desire to placate a “peevish old man.” In the end, there was a poetic resolution to the tension between the two men: When Elizabeth Hevelius had her husband’s star catalogue printed in 1690, three years after Hevelius’ death, She included Halley’s own catalogue of the stars of the southern hemisphere, which was based on Halley’s observations made on St. Helena with the 2-ft quadrant, just before his visit to Hevelius in 1679.

VD17 39:125045B; DSB 6, 363; Honeyman 1675. For a thorough discussion of the Hevelius-Hooke controversy, see Saridakis, “Converging Elements in the Development of Late Seventeenth-Century Disciplinary Astronomy: Instrumentation, Education, and the Hevelius-Hooke Controversy”, p. 129 ff.; For an assessment of the relative accuracy of Halley’s and Hevelius’ computations at Danzig, see Cook, “Edmond Halley: Charting the Heavens and the Seas”, p. 93 ff.; For Hevelius’ work on the binary star Mira Ceti, see Hatch, “Hevelius- History and Identity”, in “Change and Continuity in Early Modern Cosmology”, p 158 ff.; For D. Capellus’ contemporary account of the fire and a detailed inventory of Hevelius’ losses, see MacPike, “Hevelius, Flamsteed, Halley”, Appendix I. (London, 1937)