MISCELLANY. 



759 



ably modified for the purpose. There was 

 a beautiful adaptation of means to an end, 

 and a mutual interdependence between the 

 plant and the animal. Prof. Riley then 

 explained succinctly how, on Darwinian 

 grounds, even this perfect adaptation was 

 doubtless brought about by slow degrees. 

 He alluded, in closing, to a practical phase 

 of the subject. The plant and its fructifier 

 are inseparable under natural conditions, 

 and the fructifier is found in the native 

 home of the plant. In the more northerly 

 parts of the United States and in Europe, 

 where our yuccas have been introduced, 

 and are cultivated for their showy blossoms, 

 the insect does not exist, and consequently 

 the yuccas never produce seed in those 

 places. The larva of pronuba eats through 

 the yucca-capsule in which it fed, enters 

 the ground, and hibernates there in an oval 

 silken cocoon. In this state the insect 

 may easily be sent by mail from one part 

 of the world to another, and our own florists 

 may, by introducing it, soon have the satis- 

 faction of seeing their American yuccas 

 produce seed, from which new plants can 

 be grown. 



This paper was extremely interesting to 

 every one present, and those who discussed 

 it pronounced it in every respect admirable. 

 Dr. Asa Gray, than whom no one in the 

 country is better able to form a sound 

 opinion upon such a subject, complimented 

 Prof. Eiley on his discovery, and the lucid- 

 ity of his explanation before the section. 



Binary Stars, The same journal gives 

 a sketch of a paper on this subject by 

 Prof. Daniel Kirkwood, of which the fol- 

 lowing is a summary : 



At the meeting of the Eoyal Astronomi- 

 cal Society of London, on May 18, 1872, it 

 was announced by Mr. Wilson that a dis- 

 cussion of all the observations of the 

 double star Castor, from 1*719 to the pres- 

 ent time, had led to the remarkable conclu- 

 sion that the components are moving in 

 hyperbolas, and, consequently, that their 

 mutual relations as members of a system 

 are but temporary. The fact, if confirmed, 

 will be regarded with great interest, and 

 its discovery will doubtless be followed by a 

 minute and vigilant scrutiny of other binary 

 svstems. 



But, while such a relation as that dis- 

 covered by Mr. Wilson had not been pre- 

 viously suspected, its existence was certain- 

 ly not altogether improbable. As the sun 

 in his progressive motion througli space 

 compels such cometary matter as may come 

 within the sphere of its influence to move 

 about him in parabolas or hyperbolas, so 

 two bodies of the same order of magnitude 

 may be brought by their proper motions 

 within such proximity that their mutual 

 attraction shall cause each to move about 

 the other in a hyperbolic orbit. Such in- 

 stances, however, would seem to be ex- 

 ceptions to the general rule, as the motion 

 of most binary stars is undoubtedly elliptic. 

 (This fact has been explained in 1864 by 

 the author on the basis of the nebular hy- 

 pothesis.) 



The components of Castor are of the 

 magnitudes three and three and a half re- 

 spectively. If we suppose that each before 

 the epoch of their physical connection was 

 the centre of a planetary system, the re- 

 sults of perturbation must have been ex- 

 tremely disastrous. The two stars were at 

 their least distance in 1858. 



This alleged discovery of a temporary 

 physical connection between two fixed stars 

 suggests a number of interesting inquiries. 

 In the infinitely varied and complicated 

 movements of the sidereal systems, different 

 bodies may be brought into such juxtaposi- 

 tion as to change not only the direction of 

 their motions, but also the orbits of their 

 dependent planets. Some stars, at the rate 

 of motion indicated by the spectroscope, 

 would pass over an interval equal to that 

 which separates us from the nearest neigh- 

 boring systems in 20,000 years. In view 

 of these facts, the conjecture of Poisson, 

 that the temperature of the earth's surface 

 at different epochs has depended upon the 

 high or low temperature of the portions of 

 space through which the solar system has 

 passed, may not be wholly improbable. 



A possible origin of binary systems is 

 also indicated by Mr. Wilson's discovery. 

 The cometary eccentricity of the orbits of 

 these bodies is well known. In some cases 

 the estimated distance between the com- 

 ponents at the time of their periastral pas- 

 sage is less than half the radius of the 

 earth's orbit. Now, if at the epoch of the 



