NATURE 



?^n 



THURSDAY, FEBRUARY 9, 1893. 



THE MILKY WA V. 

 The Milky Way from the North Pole to 10" of South 

 Declination^ drawn at the Earl of Rosse's Observa- 

 tory at Birr Castle. By Otto Boeddicker. (London : 

 Longmans, Green, and Co., 1892.) 

 pvR. OTTO BOF.DDICKER devoted the clear moon- 

 L^ less nights for five years, from October 1884 to 

 October 1889, to delineating the Milky Way as it ap- 

 peared to his unaided eyes at Parsonstown, Ireland. His 

 drawings were deposited in the library of the Royal 

 Astronomical Society, and a note accompanying them 

 was read at the meeting of the Society in November 

 1889. The work now before us consists of four excellent 

 lithographic reproductions of these drawings, a brief 

 introductory preface being added by Dr. Boeddicker. 



The working maps for the drawings were taken from 

 Argelander's " Uranometria Nova," the Milky Way being 

 inserted by means of stump and lead pencil. This 

 medium was found very unsuitable for photographic re- 

 production, and in preparing the lithographic stones for 

 these charts photography was used for the stars, and the 

 Milky Way was introduced by hand work. Mr. W. H. 

 Wesley, the Assistant Secretary of the Royal Astronomical 

 Society, is responsible for this latter portion of the work, 

 and the results are a splendid testimony to his care and 

 skill. Dr. Boeddicker is to be congratulated upon having 

 secured the services of so excellent an artist. 



Plate L is a detailed drawing of the Section Cygnus- 

 Scutum, Plate II. of the Section Cassiopeia?, and Plate III. 

 of the Section Aurigas-Gemini-Monocerotis. In these 

 plates an attempt has been made to represent accurately 

 the appearance of the galaxy, all the differences of 

 luminosity being represented as they actually appeared 

 to Dr. Boeddicker. In Plate IV. a general view on a 

 smaller scale of the whole Milky Way from the North 

 Pole to 10° south declination is given, the contrast being 

 deliberately exaggerated in order to bring out clearly all 

 the details. 



The area of the Milky Way indicated on these drawings 

 is very much greater than that on any previously published 

 representations, while for delicate details and faithful 

 reproduction of contrast the plates are unapproached. 

 In many respects Dr. Boeddicker's drawings are a new 

 revelation, branches, wisps, and feelers being shown ex- 

 tending from the main body so as to include stars, clusters 

 and nebul«, and even whole constellations not previously 

 recognized as connected with or forming part of the 

 Milky Way. Polaris, y Arietis, Prcesepe, the Pleiades, 

 the Hyades, the great nebula in Andromeda, and nearly 

 the whole of the constellation Orion, are thus joined to 

 the galactic circle. Numerous bright patches, channels, 

 rifts, and interlacing lines of luminous matter hitherto 

 unsuspected are revealed by Dr. Boeddicker's long and 

 patient work, and exponents of disc, spiral, and other 

 theories as to the construction of the Milky Way will 

 find considerable difficulty in accounting for the details 

 shown. 



It is very difficult to compare drawings of the Milky 

 Way made by different observers without optical aid. 

 NO. 12 15, VOL. 47J 



There are such wide variations in unaided vision, so 

 many peculiarities introduced by long and short sight, by 

 astigmatism, by irradiation in the retina, and by other 

 physical and physiological imperfections, that it may 

 safely be asserted that no two persons get exactly the 

 same naked-eye impression of such a vague object as 

 the Milky Way. As no details are given about Dr. 

 Boeddicker's eyes we are probably justified in inferring 

 that they are practically normal, but we doubt whether 

 any other observer, even with special training, could 

 check or correct these charts with reasonable prospect of 

 convincing the original artist of error in the representa- 

 tion of the Milky Way as it appeared to him. Individual 

 peculiarities of sight are minimized by the use of slight 

 optical aid, and two equally experienced observers would 

 be more likely to agree in their delineations of the Milky 

 Way if they used similar telescopes, of say j-inch aper- 

 ture, or even ordinary opera glasses. Dr. Boeddicker's 

 appeal to other observers to " verify and correct " his 

 work will probably bring him plenty of correspondence, 

 but can scarcely lead to any important correction in his 

 magnificent drawings. 



Dr. Boeddicker considers that " the first step necessary 

 towards the knowledge of the sidereal universe is a 

 thorough acquaintance with the Milky Way as it appears 

 to the naked eye," and hopes that by comparison and the 

 superposition of naked-eye drawings on photographs 

 " some knowledge of the structure of the Milky Way in 

 the line of sight may be obtained.'' This idea is founded 

 on the theory that there is a direct connection between 

 the magnitudes of stars and their distances. Littrow's 

 analysis of Argelander's catalogue of stars certainly 

 seemed to justify belief in this connection, but recent 

 work has entirely disproved the hypothesis. Measure- 

 ments of the parallax of stars indubitably prove that 

 some faint stars are near, while some of the brightest are 

 at such distances as to have no appreciable parallax. 

 Thus a Ononis, a Virginis, a Leonis, and a Cygni have 

 no parallax, while the 5th magnitude star 61 Cygni has a 

 parallax of between o"-4 and o"-5. Photographs of the 

 Pleiades show that we have in that cluster stars differing 

 by as much as 13 magnitudes at approximately the same 

 distance from us. Russell's photograph of a Crucis 

 plainly indicates a direct physical connection between 

 that star and many stars of the 14th and 15th magnitudes 

 which should, according to the theory, be nearly 1000 

 times more distant. Streaks of nebulae connect a Cygni 

 and y Cygni with long lines and stars of about the 16th 

 magnitude in Dr. Max Wolf's photographs of the 

 Milky Way. From considerations of parallax observa- 

 tions of stars and from examination of photographs we 

 are forced to conclude that there is no real connection 

 between magnitude and distance, and that the differences 

 of magnitude of stars are due to differences of size and 

 physical condition. Stars differ enormously in light- 

 giving power, and the actual light emitted by a Cygni 

 must be nearly a million times greater than that from the 

 faint stars directly connected with it and at practically 

 the same distance from us. There is therefore very little 

 chance of adding to our knowledge of the Milky Way 

 "in the line of sight" by superposition of naked-eye 

 drawings on photographs. 



In his preface Dr. Boeddicker frequently speaks of 



