ASTRONOMICAL PHENOMENA AND PROGRESS. 



38 



0-4306; of those whose periods exceed 200 

 years, 0*6055. . . 



New Double Stars. A new companion of 

 Aldebaran lias been discovered by Mr. . W. 

 Burnham of Chicago, at the distance of only 

 30" from the large star. It is very faint, be- 

 ing about equal in apparent magnitude to the 

 omer satellite of Mars. In February, 1878, 

 the same distinguished observer discovered 

 the companion of Rigel to be undoubtedly 

 double. The instrument used in his observa- 

 tions was the 18^-inch Clark equatorial of the 

 Chicago Observatory. Mr. Burnham calls at- 

 tention also to the star 99 Herculis, whose 

 duplicity was discovered by Mr. Alvan Clark 

 in 1859. The companion, since the date of its 

 discovery, has undergone a change of 42 in its 

 angular position. The components, therefore, 

 in all probability, constitute a binary system. 



Birmingham on Bed Stars.NLr. Birmingham 

 of England has been engaged for several years 

 on the observations of red stars, and has re- 

 cently published some interesting results and 

 speculations in the " Transactions of the Royal 

 .Irish Academy." His catalogue contains 658 

 'of these objects, with descriptions by himself 

 or references to the observations of other as- 

 tronomers. According to Mr. Birmingham, 

 red stars are to be found chiefly in a particu- 

 lar part of the heavens, viz., that part of the 

 Milky Way extending through the constella- 

 tions Aquila, Lyra, and Cygnus. It is noticed, 

 moreover, that a large proportion of the red 

 stars are variable, and that the intensity of 

 their color varies inversely with the apparent 

 magnitude. Mr. Birmingham refers these 

 phenomena to the existence of nebulous rings 

 with an accumulation of matter on one side, 

 and more or less absorption of some of the 

 colored rays, according to the densities of the 

 different sections. The color of the red stars 

 which are not variable may be due, he sup- 

 poses, to a permanent atmosphere. Mr. Bir- 

 mingham's memoir contains a collection and 

 discussion of the spectroscopic observations of 

 Huggins, Secchi, Vogel, and D'Arrest. 



Relation between the Colors and Periods of 

 Variable Stars. The " Science Observer " for 

 July, 1878, contains a paper by Mr. Seth 0. 

 Chandler of Boston on the relation between 

 the colors of variable stars and the lengths of 

 their periods. In Schonfeld's catalogue of 138 

 variable stars he finds 26 whose colors are not 

 given, or whose periods are irregular. De- 

 ducting these, he arranges the remaining 112 

 in classes according to the length of their 

 periods, separating the red or reddish from 

 those noted as white, yellow, or of no decided 

 color. The result is as follows: 



It is seen at a glance that the number of red 

 stars increases with the length of the period, 

 while that of ' white or colorless stars de- 

 creases. 



The stars are next classified according to 

 their colors, and the average period of each 

 class computed. The result is shown in the 

 table below : 



" The progressive increase in the value of the 

 average period from the white stars at the one 

 end of the scale to the intense red at the other 

 end is very remarkable." 



The Origin of Nebulae. The "Philosophical 

 Magazine " for July, 1878, contains an article 

 on the origin of nebulae by Dr. James Croll 

 of Scotland. Laplace and other writers on 

 Cosmogony had assumed the existence of mat- 

 ter in a state of gaseous diffusion, and had 

 shown how the solar and sidereal systems 

 may have been formed by the process of con- 

 densation, and how future systems may be 

 evolved in like manner from existing nebuleo ; 

 but what the previous condition of a nebula 

 was, or what physical cause had produced its 

 present gaseous state, they had never inquired. 

 The object of Dr. Croll's memoir is " to ex- 

 amine the bearings of the modern science of 

 energy on the question of the origin of nebu- 

 la, and in particular to consider the physical 

 cause of the dispersion of matter into stellar 

 space in the nebular form." 



A brief view of Dr, Croll's hypothesis may 

 be presented as follows: The so-called fixed 

 stars are well known to have a proper motion 

 in space. Reasons are not wanting for be- 

 lieving that non-luminous bodies also exist, in 

 indefinite numbers, moving in all possible di- 

 rections, and with various degrees of velocity. 

 The occasional impact of these opaque stars 

 would be a necessary consequence. With great 

 velocity at the moment of collision, sufficient 

 heat might be developed to reduce the united 

 mass to the form of a gaseous nebula. Such 

 is supposed to have been the origin of the 

 thousands of nebulae revealed by the telescope. 

 The fixed stars have been produced by the 

 condensation of ancient nebulae. These as they 

 cool down must gradually become extinct, to 

 continue their motion as non-luminous bodies 

 until a new encounter, in the distant future, 

 shall reconvert them into nebulse. 



The process by which opaque stars are sup- 

 posed to have been transformed into nebulse is 

 thus given in Dr. Croll's very interesting me- 

 moir : 



Take the case of the origin of the nebulous mass 

 out of which our sun is believed to have been formed . 

 Suppose two bodies, each one half the mass of the 

 sun, approaching each other directly at the rate of 



