February marks the sesquicentenary of the

birth of the notable Danish astronomer

John Louis Emil Dreyer in Copenhagen

on 13 February 1852 (K[nobel] 1927). His

interest in astronomy was sparked when, as a

young teenager, he read a book on Tycho

Brahe and his observatories. Following this, he

was introduced to, and had many stimulating

conversations with, Prof. Hans K F K

Schjellerup, the Observator at Copenhagen

Observatory. At the University of Copenhagen

he attended the astronomy lectures of his

supervisor, Prof. H d’Arrest, and won the uni-

versity’s prize question Gold Medal in 1874 for

a paper on personal errors in observations

(Dreyer 1876). He received his doctorate from

the University of Copenhagen too.

Dreyer was appointed astronomer at the Earl

of Rosse’s Observatory at Birr Castle, Co.

Offaly, Ireland, in 1874, a position he held for

four years. While at Birr he had full use of the

world’s then-largest telescope, the 72 inch

reflector. Here Dreyer made advances in the

study of nebulae and clusters of stars, publish-

ing a supplement to the General Catalogue ofNebulae by Sir John Herschel, extending that

list by more than 1100 nebulae (Dreyer 1877).

In 1878 he became assistant at Dunsink Obser-

vatory near Dublin where his main duties

included meridian observations. Dreyer suc-

ceeded Dr T R Robinson as Director of the

Armagh Observatory in 1882.

Combining catalogues

In 1886 the Council of the Royal Astronomical

Society suggested that Dreyer should combine

the three principal catalogues of nebulae,

namely those of Sir John Herschel (including

Dreyer’s revision), D’Arrest and the Fourth

Earl of Rosse. The renowned New GeneralCatalogue of Nebulae and Clusters of Stars(NGC) was thus born in 1888 (Dreyer 1890).

In this work Dreyer regretted the necessity of

introducing a new numbering system, which he

hoped would be used as little as possible and

that the original identifiers, H and h, of the

two Herschels would instead be retained. Two

further supplements to the NGC were pub-

lished (Dreyer 1895, 1910) known as the IndexCatalogues, which brought the total number of

objects to 13 226. One of the treasures in the

Armagh Observatory collection is Dreyer’s per-

sonal copy of the timeless NGC annotated

with notes by the author including all correc-

tions known to him.

Dreyer investigated the history of determina-

tions of the precessional “constant”, especially

those made by Bessel, Struve and Nyrén (who

compared the catalogues of Bradley and T R

Robinson [Robinson 1859]), and also made a

new determination himself (Dreyer 1882,

1883). In 1897, as a consequence of the “Inter-

national catalogue of fundamental stars” con-

ference held in Paris in 1896, Simon Newcomb

was requested to derive a definitive value for

the precessional constant (Newcomb 1897).

Newcomb incorporated Dreyer’s determina-

tion in his analysis, albeit slightly modified due

to later findings.

Brahe biography

An eminent scholar of the history of astrono-

my, Dreyer wrote the standard biography of

Tycho Brahe (Dreyer 1890) and edited in Latin

the collected works of that early Danish

astronomer in a 15-volume series that was

published between 1913 and 1929 (Dreyer

1913–29), a truly monumental work. Another

of his masterpieces was the history of planetary

systems from Thales of Miletus to Kepler

which was published in 1906 (Dreyer 1906).

He also collated the scientific papers and wrote

a short biography of Sir William Herschel

(Dreyer 1912).

History of the RAS

Dreyer resigned his position at Armagh in 1916

to continue his historical researches at Oxford

(Bennett 1990). With H H Turner he wrote the

history of the first century of the Royal Astro-

nomical Society (Dreyer and Turner 1923).

Dreyer was the 1916 recipient of the Gold

Medal of the RAS for his contributions to

astronomical history and for his catalogues of

nebulae (Sampson 1916). He also served as the

Society’s President from 1923–25. Dr Dreyer

died at Oxford on 14 September 1926. �

John McFarland, Armagh Observatory, CollegeHill, Armagh, Northern Ireland BT61 9DG.

ReferencesBennett J A 1990 Church, State and Astronomy in Ireland: 200 Yearsof Armagh Observatory Institute of Irish Studies, The Queen’sUniversity of Belfast and Armagh Observatory.Dreyer J L E 1876 Proc. Roy. Irish Acad. Second Series 2 Science484–528.Dreyer J L E 1879 A Supplement to Sir John Herschel’s ‘GeneralCatalogue of Nebulæ and Clusters of Stars. Trans. Roy. Irish Acad. 26Science 381–426.Dreyer J L E 1882 Copernicus 2 135–155.Dreyer J L E 1883 Proc. Roy. Irish Acad. Second Series 3 Science617–623.Dreyer J L E 1890 A New General Catalogue of Nebulæ and Clustersof Stars, being the catalogue of the late Sir John Herschel, Bart.,revised, corrected and enlarged Mem. RAS 49 1–237.Dreyer J L E 1890 Tycho Brahe: A picture of Scientific Life and workin the Sixteenth Century Adam and Charles Black, Edinburgh.Dreyer J L E 1895 Index Catalogue of Nebulæ found in the years1888 to 1894, with Notes and Corrections to the New GeneralCatalogue Mem. RAS 51 185–228.Dreyer J L E 1906 History of the Planetary Systems from Thales toKepler Cambridge University Press, revised by W H Stahl as: A Historyof Astronomy from Thales to Kepler Dover Publications, Inc. 1953.Dreyer J L E 1910 Second Index Catalogue of Nebulæ and Clustersof Stars, containing objects found in the years 1895 to 1907; withNotes and Corrections to the New General Catalogue and to the IndexCatalogue for 1888–94 Mem. RAS 59 105–198.Dreyer J L E 1912 The scientific papers of Sir William HerschelLondon.Dreyer J L E and H H Turner 1923 History of the Royal AstronomicalSociety Royal Society/Royal Astronomical Society.Dreyer J L E 1913–29 Tychonus Brahe Dani Opera Omnia Hauniae.K[nobel] E B 1927 Obituary Notice MNRAS 87 251–257.Newcomb S 1897 Astronomical Papers of the American Ephemeris8 1–76.Robinson T R 1859 Places of 5345 stars observed from 1828 to1854 at the Armagh Observatory A Thom and Sons, Dublin.Sampson R A 1916 The President’s Address on presenting the GoldMedal of the Royal Astronomical Society to Dr J L E Dreyer MNRAS76 368–375.

1.22 February 2002 Vol 43

J L E Dreyer

Dreyer’s sesquicentennial

1: J L E Dreyer at Armagh Observatory

2: The title page of Dreyer’s personalcopy of his NGC.

John McFarland marks 150 years

since the birth of J L E Dreyer.