June 15, 1882] 



NA TURE 



'55 



more than 1000 observations up to this. Latterly, this 

 branch of science has made distinct advances in Ame- 

 rica, where Burnham has made excellent use of the 

 gigantic refractors, which are made by Alvan Clark of 

 Boston. He has discovered a number of important 

 double stars, the components of which cannot be sepa- 

 rated at all in older telescopes. 1 



In 1878 the French astronomer Flammarion, who is so 

 favourably known from his excellent popular treatises, 

 published his " Catalogue des Etoiles doubles et multiples 

 en Mouvement relatif certain, comprenant toutes les 

 Observations faites sur chaque couple depuis sa de"cou- 

 verte, et les re'sultats conclus de l'Etude des mouvements," 

 a work that is highly valued by double-star investi- 

 gators, but private observers will do well in consulting 

 also Messrs. Crossley, Gledhill, and Wilson's " Hand- 

 book of double-Stars," with its "Supplement." 



As remarked above Herschel found that changes had 

 taken place in several systems of double-stars, and in 

 1836 Struve was able to give a list of a hundred systems, 

 where the components appeared to revolve ; but on 

 account of the difficulty of the measures, it was not easy 

 to decide whether this was owing to actual motion of the 

 star or in some cases to divergences of the observations. 

 But he proved beyond dispute in about half the cases 

 that the companion had revolved, and Madler, who was 

 one of the most indefatigable double-star observers, as 

 well as the most prominent calculator, raised this number 

 to several hundreds. His work, " Tabula generalis 

 stellarum duplicium indicationem motus gyratorii ex- 

 hibentium," was published in 1849, and contains 650 

 entries, but many of the=e were mere surmises, and have 

 not been corroborated by subsequent research. 



If the observations were absolutely free from errors, it 

 would be an easy task to investigate the path of the com- 

 panion, but in addition to the imperfection of every 

 observed position, we have as explained above to guard 

 against systematic differences between the different ob- 

 servers. In long series of observations of quickly 

 revolving stars, this gives occasion to endless discussion. 

 We draw, for instance, a powerful aid in discerning sys- 

 tematic errors, from Kepler's law, that the areas described 

 by the radius vector are proportional to the intervals of 

 time ; but he would be a bold man, who in the present 

 state of our knowledge, would affirm that all binary stars 

 have been proved to revolve according to this law in 

 elliptic orbits, in the focus of which the mai:i star is 

 situated,' 2 or would condemn all observations that could 

 not be made to fit into such an hypothesis. But though 

 this assumption is a mere hypothesis, and may remain so 

 for a long time to come, we have nothing else to guide 

 us. In fact we cannot calculate an orbit at all except by 

 aid of these laws. 3 W. Doberck 



( To be continued.) 



1 The difficulty of separating close double stars renders then, fit tests for 

 the performance of a telescope. Some i lea cf the quality of a telescope may 

 be gained, when it is stated that it is able to separate objects of a certain 

 class, be it lucid-* or rvligva, but withal, it is preferable to try us perform- 

 ance on terrestrial test objects. A third sub class " delicate " double stars, 

 or those in which the companion is so minute compared to the main star, as 

 to require a high degree of optical power to perceive it, has been added by 

 Sir John Herschel, but it deserves to be remarked that the appearance of 

 such objects depends quite as much upon the slate of the atmosphere. I he 

 companion of Sinus, f.r instance, has been repeatedly seen in 4. inch re- 

 fractors under exceptionally favourable circumstances, though in a great 

 latitude. A large acerlure is therefore not always an advantage. The situation 

 observatory isof much greater importance. Piazzi Smyth has the merit 

 of having for years insisted upon this point. The Lick Observatory, about 

 to be founded on Mount Hamilton, California, will offer unusual advantages. 

 Mr. Burnham has there already discovered some difficult double stars u ith a 

 m nor telescope. 



- Both stars revolve, of course, round their common centre of gravity, but 

 it is easy to see that the relative position of the two stars is all the same then 

 as if only one revolved. If the changes in the absolute place of one of the 

 stars were known, we would have the means of computing the relative 

 masses ; but this has only been possible in a few cases at most. 



3 In case of certain triple stars, whose movements do not fit into 

 Keplerian ellipses, we have to represent the motions by aid of epicycles, just 

 in the same way as PtoJemaeus represented the motion of the planets in the 

 system named after him. 



THE MARIANNE NORTH GALLER Y OF PAINT- 

 INGS OF " PLANTS AND THEIR HOMES," 

 ROYAL GARDENS, KEW 



MANY readers of Nature are doubtless aware that 

 the large collection of beautiful and instructive 

 pictures of flowers painted in various countries by Miss 

 Marianne North, is now, through the noble generosity of 

 this lady, the property of the nation. The collection is in 

 a handsome building specially erected in Kew Gardens 

 for the purpose, at Miss North's expense, and from 

 designs given by Mr. James Ferguson, F.R.S. Last week 

 the gallery was opened without any ceremony whatever, 

 and henceforward it will be open and free to the public 

 at the same times and hours as the museums and other 

 buildings in the Gardens. 



Now that this is an accomplished fact, a few words 

 respecting the history and the principal features of the 

 collection may be useful. Impelled by a love of nature, 

 Miss North has spent many years travelling from country 

 to country, and painting the most striking scenes and 

 objects that came under her observation ; and from 

 time to time some of these paintings have been exhibited 

 in London. The more Miss North travelled and painted, 

 the more the desire to travel and paint seems to have 

 grown ; the result being a large collection of pictures. 

 Then arose the question, what should be done with them? 

 and happily in this Miss North was influenced by 

 the kindly feeling that she would like other less fortunate 

 persons to see and enjoy what she herself had seen and 

 enjoyed so much. This idea once conceived, the warm- 

 hearted artist and traveller set to work more assiduously 

 than before, in order to carry it into effect, even visiting 

 Australia and New Zealand, for the purpose of painting 

 the vegetation of that region. In a country where the 

 love of flowers is general from the poorest to the richest, 

 such a gift as that now offered to the public will assuredly 

 be fully appreciated. 



The collection is designated in the title of the catalogue 

 as paintings of " plants and their homes," and this title 

 is justified by the fact, that in nearly all the pictures, 

 plants have supplied the motive, the other objects repre- 

 sented being accessories. Altogether there are upwards 

 of six hundred pictures, representing vegetation in nearly 

 all temperate and tropical parts of the world except 

 Europe and Africa, unless we regard Teneriffe as belong- 

 ing to the latter country. A descriptive catalogue, com- 

 piled by the writer of this notice, and published at Miss 

 North's expense, contains not only the titles of the pic- 

 tures, but aKo short notes concerning the life-history, 

 products, Sec, of the plants painted, inserted with the 

 intention of making it as instructive as possible to those 

 who know least of such things. There are representa- 

 tions probably of not less than a thousand species, and 

 these include members of nearly every natural order in 

 the vegetable kingdom. The fruit and other useful plants 

 of the different countries are numerous ; and associated 

 with them are many of the most ornamental and most 

 striking wild and cultivated plants. In dealing with trees 

 and shrubs, the artist has usually painted a flower-bearing 

 or fruit-bearing branch, or both, in front, and given the 

 habit of the tree or shrub in a landscape behind. With- 

 out being botanical, the paintings of the plants are 

 so thoroughly naturalistic, that a botanist has little dif- 

 ficulty in determining such as are not known to him 

 by sight. In so far as regards its prominent features 

 and peculiar types, the Australian flora is more com- 

 pletely portrayed than any , other, about seventy-five 

 pictures being devoted to this region. Miss North 

 visited Queensland, New South Wales, Victoria, Tas- 

 mania, South Australia, and West Australia ; and from 

 each of these colonies she brought home paintings of a 

 large number of the most striking and characteristic 

 plants. Thus of Eucalyptus there are portraits of E 



