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Emmanuel Liais and the cœlostat

Notes on a forgotten instrument


Maria Lucia de Niemeyer Matheus Loureiro


Museu de Astronomia e Ciências Afins – MAST (Rio de Janeiro, Brazil)


Vitor Luiz Silva de Almeida


UFRJ/PPGHC – Universidade Federal do Rio de Janeiro

Programa de Pós-Graduação em História Comparada

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In 1895, Gabriel Lippmann describes a new instrument, the cœlostat, an improvement on the siderostat, which would give a fixed image of the entire sky.  In 1874, more than two decades before Lippmann, French astronomer Emmanuel Liais, the then director of the Imperial Observatory of Rio de Janeiro, designed and ordered the construction of an apparatus (also called a cœlostat) for the same purpose, which the great advantage was its potential to photograph the sky.  Taking all its parts into account, the cœlostat would take up more than 15 metres in length, making impossible for it to be assembled at the time, since the observatory was located on cramped premises on Castelo Hill.  Apparently, Liais’s cœlostat was never used.  It is not known what happened to the instrument, and its disappearance probably resulted from the lack of any suitable space for its use and conservation.

 Keywords:  cœlostat, Emmanuel Liais, Imperial Observatory of Rio de Janeiro



Emmanuel Liais e o celóstato: Notas sobre um instrumento esquecido

Em 1895, Gabriel Lippmann descreve um novo instrumento, o celóstato, um aperfeiçoamento do siderostato, destinado a proporcionar uma imagem fixa do céu. Em 1874, mais de duas décadas antes de Lippmann, o astrônomo francês Emmanuel Liais, então diretor do Imperial Observatório do Rio de Janeiro, projetou e supervisionou a construção de um aparato (também chamado celóstato) para o mesmo propósito, cuja grande vantagem era o potencial para fotografar o céu. Levando em conta todas as suas partes, o instrumento ocupava mais de 15 metros de comprimento, tornando impossível sua montagem nas instalações exíguas do Morro do Castelo. Aparentemente, o celóstato de Liais jamais foi usado. O destino do instrumento é ignorado, e seu desaparecimento resultou provavelmente de falta de espaço adequado para seu uso e conservação.

Palavras-chave:  celóstato, Emmanuel Liais, Imperial Observatório do Rio de Janeiro.


In 1895, The Observatory journal published a three-page article by Gabriel Lippmann entitled The cœlostat”.  In his text, Lippmann describes an instrument that was an improvement on “Foucault’s siderostat”, the principle of which was well known at the time (ref. 1).  The siderostat could produce a static image of a star reflected in a mirror, enabling it to be observed through a fixed telescope.  However, the image of the sky itself did not remain static, which was a problem Lippmann claimed to have solved: “In the mirror of a siderostat (…) the image of the sky itself is not stationary: the remaining stars appear to move around the selected star.  Would it be possible to construct an apparatus which would give a fixed image of the entire sky, which would therefore be not a siderostat, but a cœlostat?  There is a solution of this problem and one only, which is here given.  A plane mirror is mounted on an axis which rests on two fixed bearings.  The mirror and its axis are parallel to the line joining the celestial poles.  Uniform motion is given to the system, so that it may make a complete rotation about the axis in 48 hours, in the same direction as the apparent diurnal motion of the heavens.”  According to its inventor, the new instrument would work like an equatorial telescope, but its advantage lay in its precision and simplicity and the fact that the observer did not have to move (ref. 2).


A member of Académie des Sciences (Paris), the Royal Society (London) and Bureau de Longitudes (Paris), Gabriel Lippmann is known to this day as the inventor of the cœlostat and for having won the Nobel Prize in Physics in 1908.  The Nobel Prize website states that Lippmann “contributed to astronomy with his invention of the cœlostat, a device which immobilizes the image of a star and its surrounding stars so that a photograph may be taken.  He was also responsible for many more ingenious devices and improvements to standard instruments to the benefit of many branches of physics” (ref. 3).


The invention of the cœlostat in 1895 was immediately applauded by the scientific community.  The Transactions of the Astronomical and Physical Society of Toronto for 1895, published the following year, announced “a new instrument invented by M. Lippmann, called the cœlostat, whereby a star and the whole stellar vault presents a steady image for the purposes of observation.  A plain mirror is mounted on an axis parallel to a line joining the celestial poles, and by clock-work the whole apparatus is rotated in forty-eight hours” (ref. 4).


Mills confirms that Lippmann’s invention “immediately attracted the attention of both professional and amateur astronomers, although according to Hartman it was a re-invention of a design originally produced by E.E. August before 1839”.  According to August, the two-mirror cœlostat was the only possible way of obtaining a non-rotating image of the Sun, and adds that currently, the complete two-mirror system is often called a “cœlostat” (ref. 1).

In the first decade of 20th century, American astronomer George E. Hale devised a new apparatus for solar research: the Hale cœlostat, also known as ‘the Snow Telescope’.  The instrument consisted of a fixed telescope fed by a cœlostat with a secondary mirror, able to provide stationary and sharply defined images of Sun (ref. 5, 6)


In 1874, more than two decades before Lippmann announced his invention, and more than thirty years before the construction of Hale’s cœlostat, French astronomer Emmanuel Liais (1826-1900), then the director of the Imperial Astronomical Observatory of Rio de Janeiro, returned to Brazil after a trip to Europe with the dual purpose of publishing the findings of his scientific explorations in Brazil and above all to “oversee the construction of part of the material required for the development of the Imperial Observatory, which could not be executed in the country” (ref. 7).


Liais ran the observatory from 1870 to 1883, when he was replaced by an interim director, Luiz Crulz.  His time at the institution was marked by a desire to drive progress in astronomy in Brazil, and by economic and physical obstacles which he struggled to overcome to make the observatory a place of scientific excellence in a class of its own not just in Brazil but in all of the Americas.

Not only was Liais a remarkable astronomer, he was also an inventor.  According to Heizer (ref. 8), in 1869 José Maria dos Reis requested and was granted the privilege of manufacturing an azimuth instrument created by the French astronomer (ref. 9).  Freitas Filho reports that the new equipment “increased the precision of observations of azimuths, and could also be used to measure heights” (ref. 10).


For Granato and Santos (ref. 11), one of the instruments devised by Liais (the altazimuth) won “a number of awards in different exhibitions in Brazil and Europe” (Fig. 1).  According to Auxiliador da Indústria Nacional, a national industry periodical, the exhibition held in 1889 in Rio de Janeiro in preparation for the Exposition Universelle in Paris contained a number of instruments manufactured by José Hermida Pazos (ref. 12), including “an altazimuth with an objective prism, and a collimator, invented by the great man Liais”, which earned him an honorary diploma.  In Paris in the same year, Liais’s “new azimuthal telescope” was awarded a silver medal (ref. 13).

Altazimuth by Liais

Fig. 1: Altazimuth by Liais. MAST collection. Illustration based on a photograph. (ref. 15)


According to Liais, the instruments acquired in 1874 in France would allow the Observatory of Rio de Janeiro to take “the place it deserves amongst the leading establishments of the same kind in other countries”.  The material was packed into 21 cases and shipped from Europe on a steamer called the Rio Grande.  Other shipments had also been sent before he had left France, and the astronomer himself brought one “precious objective lens” in his own baggage.  Liais reports that all the boxes “arrived in perfect state, and the fragile instruments they contained did not suffer at all”. According to a report on the observatory to the government, the instruments had been made on commission to Emmanuel Liais’s own designs and under his direct supervision, and contained “several improvements on ones of the same kind manufactured previously” (ref. 7).


The improvements to some of the objects, as the document attests, meant that they effectively constituted new instruments: “Such is particularly the case of our large heliostat or siderostat, which is put together in such a way that under no circumstances do the light rays diverge from the normal by more than 30 degrees; so that the rays issuing from any point in the sky may be sent in a single, fixed direction; a circumstance which until now could not be achieved with any instrument, which is why I gave it a new name, of cœlostat, which expresses its general nature and indicates that it alone serves for many siderostats.  Furthermore, this instrument has the advantage of avoiding grazing rays, which destroy the beauty and clarity of the images.  This instrument’s clockwork mechanism is not just a masterpiece of execution which dignifies the Sècretan workshops, but also has a new regulation system that is far more reliable and less complicated than Foucault’s, by which one can regulate the movement by the velocity of the body one wishes to follow, whether it is a star, a planet, the moon or the Sun.  It also has satellite gears using Gambey’s system, by which the needle can be corrected without affecting the motion.The cœlostat’s optical system also deserves very special mention, not to mention the two exceptionally flat 45-centimetre mirrors which are part of the moving system, driven by the clockwork mechanism.  The fixed system comprises two telescopes, one with a 10-metre black glass reflector for the Sun, so that its whole aperture can be employed, and another 7-metre silvered reflector for other celestial bodies.  The eyepiece system has a considerable number of combinations and all the lenses are achromatic and have a 7 and a half centimetre diameter.  Finally, the eyepiece system has a finder and is positioned in such a way that it can accommodate spectroscopes” (refs. 7, 14). 


Liais stressed that “of itself this magnificent instrument would be enough to make the Rio de Janeiro Observatory of particular interest” and would enable “research of greater interest to astronomy, which would be impossible without its capacity to fix the light rays” (ref. 7).   He nonetheless warned that taking all its parts into account, the cœlostat would take up more than 15 metres in length, which made it impossible for it to be assembled at the time, since the observatory still occupied cramped premises on Castelo hill, from which it was only transferred in the twentieth century.


Alongside the cœlostat, the instruments imported in 1874 which Liais had also designed or improved on included a spectroscope – or spectrometer, as he called it – and “chronographic apparatus to record meridian observations and observations of longitudes using electricity” (ref. 7).


In the 1882 annual report, the then acting director of the Rio de Janeiro observatory, Luis Cruls, stressed the shortage of space for large instruments to be assembled, mentioning not just the instruments imported eight years earlier by Emmanuel Liais (including those he designed) but also the material recently acquired for the observation of the transit of Venus.  The document further states that in one of the rooms of the observatory there was stored “an instrument, especially made for the Observatory and [based] on an entirely new model; it is the large cœlostat, an instrument that could render great services in the studies of astronomy” (ref. 15).


The first volume of Annales de l’Observatoire Imperial de Rio de Janeiro (the observatory’s annals) was published in French in the same year of 1882 and carried a complete description of the observatory and its instruments, including the cœlostat (Fig. 2): “The cœlostat consists of a kind of equatorial assembly designed to support two perfectly plane mirrors 45 centimetres in height.  The first receives the light rays from the celestial body and directs them to the second,

Illustration of Liais' cœlostat

Fig. 2: The cœlostat (not assembled for observation). Illustration based on a photograph (ref. 16)

which reflects the rays down the polar axis towards the north pole.  These light rays cross the lower part of the instrument’s hour angle axis, which comprises a circle with a large outer diameter with a central opening of 40 centimetres in diameter.  This circle is supported by four pulleys arranged in twos on a support that rotates around an axis.  To prevent the lower part from sliding along the hour angle axis, the upper part is finished with a sphere fixed to the support, which stops the system from slipping.  The circle that is the lower part of the hour angle axis has teeth which fit into a cog which connects to the clockwork mechanism so that the instrument accompanies diurnal motion.  The same circle has a scale on which two opposing microscopes are connected.  The instrument’s assembly consists of two very solid cast iron structures, one forming the central part of the hour angle axis which supports the two ends, and the other rotating in the middle of the first on two pins which form the shaft.  This second structure transforms the instrument from a commonplace equatorial telescope into a centralized telescope.  At the bottom of the same structure is one of the two mirrors which rotates around the axis, and at the top of the other structure which is responsible for the mid part of the hour angle axis is the second mirror, which is likewise supported by a shaft and, like the first mirror, has a circle to measure the angles that rotates in a plane around the axis.  A third circle serves to measure the angle of the two structures.  One of the structures has a counterweight and the mirrors are thus perfectly balanced.  Both mirrors are at an equal distance from the centre of rotation” (ref. 16).


The text also contains instructions on how to use the cœlostat at the Rio de Janeiro latitude and explains what features make it a better option than the siderostat, especially when it comes to the quality of the images obtained.  This improvement derives from the fact that whatever the declination of the celestial body, the new instrument enables the angle between the light rays and the mirror never to exceed 30 degrees.  The larger the angle, the bigger the mirror must be, which makes execution more demanding and augments its defects (ref. 16).


Another of the instrument’s features stressed by Liais is the potential to photograph the sky: “To instantly photograph the sky, the great stability that is provided for the photographic equipment is a great advantage, and it can be used for very large dimensions, which is impossible with telescopes.  For groups of stars or for celestial bodies for which prolonged exposure is required, it must be stressed that the image, while always the same, rotates around its centre on the plate.  In this case, with the help of the transmission obtained from the clockwork movement of the instrument (Fig. 3), it is necessary to transmit the corresponding rotation to the plate” (ref. 16).


Clockwork mechanism of the cœlostat

Fig. 3: Clockwork mechanism of the cœlostat. Illustration based on a photograph (ref. 16)


In an article on the cœlostat and the siderostat published in 1905 in the periodical, Monthly Notices of the Royal Astronomical Society, Plummer warns that “the use of a siderostat, notwithstanding the advantages that it offers, is not free from objections.  In spite of the ingenuity which has been devoted to several forms of construction it has been generally felt that the mechanical design of the instrument leaves much to be desired”.   He further recommends “the use of a cœlostat in conjunction with a second mirror, which deflects the rays from the cœlostat into a permanently fixed telescope” (ref. 17).


It would appear that Liais’s cœlostat was never used.  During the years he ran the observatory, this fact gradually became a source of great frustration for him, especially in view of his initial goals as its director.  Henrique Morize, who headed the observatory from 1908 to 1929, stated that in 1876 Liais had advised the Ministry of War of imminent “important astronomical phenomena” and was keen to “install the large instrument which, for lack of space, was still in its boxes” (ref. 18).


Two years later in his annual report to the Ministry of the Empire, Liais complained that “material of such great value as that at the National Observatory remains in a place that is so inappropriate for its use, so detrimental for its conservation as the damp premises at Castello which it currently occupies” (ref. 19).


It is not known what happened to this first cœlostat, whose disappearance probably resulted from the lack of any suitable space for its use and conservation.  In its collection, Museu de Astronomia e Ciências Afins (MAST) (ref. 20) has another cœlostat manufactured more recently which also belonged to the National Observatory.  In the dossier on this object there is a statement (ref. 21) by Odílio Ferreira Brandão, formerly the head of the National Observatory workshops, where he worked for around four decades, in which he states that he was not aware of the existence of a cœlostat by Liais.  The 1882 annals of the observatory do, however, contain detailed illustrations of the instrument (Fig. 2) and its clockwork (Fig. 3) mechanism based on photographs.


We are informed by Muniz Barreto, who ran the observatory between 1968 and 1979 and again from 1982 to 1985, that “alongside the mirrors of 0.45m in diameter for normal use, the cœlostat had a pair of reserve mirrors” which had survived at the observatory and whose “excellent quality” he had had occasion to ascertain.  He adds that in 1874 it was “a new astronomical instrument, replacing the old heliostat and siderostat” (ref. 22).


Although the instruments by Gabriel Lippmann and Emmanuel Liais are both called cœlostats, they are not similar.  One of the most striking differences is the number of mirrors: Lippmann’s design describes just one, while Liais’s had two.  However, the practical purpose of both instruments is very similar.


Like Liais, Hale warns that ‘a cœlostat should be employed, in preference to any form of heliostat or siderostat, since its causes no rotation of the solar image’.  Both instruments have similarities (the most obvious is the number of mirrors) and differences.  The fixed system of the instrument designed by Liais in 1874 comprised two telescopes, one for the Sun and another for other celestial bodies.  Hale’s cœlostat, on the other hand, was intended specifically to solar research.  There are other significant and very specific differences as the direction of the beam of light (Fig. 4 and 5) after reflection from the second mirror which, for Hale, “should be vertical, to reduce the danger of disturbances across the wave-front” (ref. 23).

Diagrams--position for observation of celestial bodies at different declinations

Fig. 4: Diagrams representing the position of Liais’s cœlostat for the observation
of celestial bodies at different declinations (ref. 16)

Optical layout to obtain a stationary solar image

Fig. 5 The Snow Telescope. A diagram showing the optical layout used
to obtain a stationary image of the Sun (ref. 5)


The aim of this article was to recover the history of Liais’s invention, raising it to a higher status, removing it from the oblivion to which it had been consigned and allowing it to take its place in the history of astronomical instrumentation.  For this reason it is imperative that Liais’s cœlostat be investigated further, not so much for issues relating to the authenticity of Lippmann’s or Hale’s instruments, but rather to better understand the ideas and scientific concerns that led to inventions of new devices for astronomical research.



We are grateful to Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (National Council for Scientific and Technological Development) for supporting this research. We also thank Dr. Randall Brooks, Claudia P. Santos, Ivo Almico, Ricardo Dias and the reviewers  of this paper for their valuable collaborations.


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References and notes:
  1. According to Allan Mills, “Any instrument which keeps a star centred in a field of view independently of the passage of time might be termed a siderostat (…)”.  The author adds that, “the only really successful astronomical single mirror siderostat was that invented by Foucault in 1862, the single mirror being preferred to minimize loss of light in stellar applications”.  A.A. Mills, “Heliostats, siderostats, and coelostats: a review of practical instruments for astronomical applications,” Journal of the British Astronomical Association 95 (1985), 89-98.
  2. M.G. Lippmann, “The cœlostat,” The Observatory 18 (1895), 301-303.
  3.  The official Web Site of the Nobel Prize.
  4. Transactions of the Astronomical and Physical Society of Toronto for the year 1895 (Toronto, Russell & Hutchison, 1896), p. 169.  (Available at
  5. The name of the instrument is a tribute to Miss Helen Snow, who sponsored its construction. The first instrument of this kind was built by Hale and G. W. Ritchey at Yerkes Observatory – University of Chicago. H. C. King, The History of Telescope. (Dover Publications, New York, 1979).
  6. In 1906, Hale announced the acquisition of the instrument by Mount Wilson Observatory (California). Before being purchased, the coelostat was loaned by University of Chicago for a period of two years, and its performance was considered very satisfactory. G. E. Hale, A 100-INCH Mirror for the Solar Observatory. Astrophysical Journal 24, 214-218 (1906).
  7. E. Liais, “Relatório apresentado a S. Ex. o Sr. Ministro e Secretário de Estado dos Negócios da Guerra, sobre o estado do Imperial Observatório Astronômico e os melhoramentos que ainda são necessários / Report submitted to the Minister and State Secretary of War Affairs, on the state of the Imperial Astronomical Observatory and the improvements that are still needed,” (Imperial Observatório do Rio de Janeiro, 1874) (available at   Liais was also observing the Sun from Rio on 26 March, 1859 when amateur French astronomer Edmond Modeste Lescarbault claimed to have observed a transit of the Sun by an “undiscovered” planet, Vulcan.  Liais was thereby able to deny the observation of the supposed planet.  This and the broad interest in the forth coming 1874 transit of Venus may have been part of the impetus for Liais’ development of the coelostat and trip to Paris seeking to have one constructed or purchase parts for his new instrument.
  8. A. Heizer, “O Tratado, o astrônomo e o instrumento”,  Revista Brasileira de História da Ciência 1 (2008), 167-177. 
  9. Decree n. 4411, September 9, 1869 (Brazil) (available at
  10. A.P. Freitas Filho, “José Maria dos Reis e Hermida Pazos: fabricantes de instrumentos científicos no Brasil (séculos XIX e XX)”, Revista de História Econômica & Economia Regional Aplicada 6 (2011), 138-159.
  11. M. Granato, C.P. Santos, in Coleções científicas luso-brasileiras: patrimônio a ser descoberto, M. Granato, M. Lourenço, Eds. (MAST/MCT, Rio de Janeiro, 2010), pp. 47-68.
  12. A disciple of José Maria dos Reis who took over the running of his workshop in Rio de Janeiro.
  13. “O Auxiliador da Indústria Nacional”, 57 (2011), pp. 78, 217 (available at
  14. On page 4 of 1874 Annual Report (see ref. 7), Liais refers to several other instruments he had devised or improved on, including spectroscopes, which in his view deserved “a new name, thanks to their improvements, of spectrometers, which suits them well, considering the precision of the measurements they provide, which has been considerably improved by my idea of optically diminishing the width of the slit so as to be able to reduce the number of prisms and to conserve far more light.  Thus it is that with 6 prisms our large electroscope produces the effect of a 96-prism electroscope without the distortion caused by such a great number of surfaces.” 
  15. L. Cruls, “Relatório apresentado ao Exmo. Sr. Conselheiro Senador, Ministro e Secretário de Estado dos Negócios do Império, pelo Diretor Interino do Imperial Observatório”/ “Report to the Hon. Senator Pedro Leão Velloso, Minister and Secretary of State for Empire Business, by Interim Director of the Imperial Observatory ” (Imperial Observatório do Rio de Janeiro, 1882) (available at
  16. E. Liais, Annales de l’Observatoire Imperial de Rio de Janeiro (Typographie et Lithographie Lombaerts & Cie, Rio de Janeiro, 1882) (available at
  17. H.C. Plummer, “Notes on the Cœlostat and siderostat”, Monthly Notices of the Royal Astronomical Society 65 (1905), 487-501.
  18. H. Morize, Observatório Astronômico: um século de história (1827-1927). (Salamandra / MAST, Rio de Janeiro, 1987).
  19. E. Liais, “Relatório ao Ministro do Império” / “Report to the Minister of Empire” (Imperial Observatório do Rio de Janeiro, 1878) (avalable at
  20. The Museum of Astronomy and Related Sciences (Rio de Janeiro, Brazil) holds the historical collection of the Observatory.
  21. Statement given by O.F. Brandão on June 18, 1998.
  22. L. M. Barreto, Observatório Nacional: 160 anos de História. (Observatório Nacional, Rio de Janeiro, 1987).
  23. G.E. Hale, “Contributions from the Solar Observatory”, Astrophysical Journal, 25 (1907), 68-74.