156 



RECORD OF SCIENCE FOR 1887 AND 



orbits ot those meteorites that are iu our collections and that were seen 

 to fall." Of these stone-falls there are three classes : («) 1 10 falls for 

 which we have statements as to the direction of the path through the 

 air; (/>) 94 falls of wliich we know the time of day; (c) 50 or more falls 

 of which the history is too scanty to give the time of day. He is led 

 to the following three propositions: 



1. The meteorites which we have in our cabinets, and which were 

 seen to fall, were originally (as a class and with a very small num- 

 ber of exceptions) moving about the sun in orbits that had inclinations 

 less than 90°; that is, their motions were direct, not retrograde. 



2. The reason why we have only this class of stones in our collections 

 is not one wholly or even mainly dependent upon the habits of men; 

 nor on the times when men are out of doors; nor on the places where 

 men live; nor on any other principle of selection acting at or after the 

 arrival of the stones at the ground. Either the stones, which are mov- 

 ing in the solar system across the earth's orbit, move in general in direct 

 orbits, or else for some reason the stones which move in retrograde 

 orbits do not in general come through the air in solid form. 



3. The perihelion-distances of nearly all the orbits in which these 

 stones moved were not less than 0.5 nor more than 1.0, the earth's 

 radius-vector being unity. {Observatory 11: 331.) 



At tbe meeting of the Royal Society, November 15, 1888, Prof. G. U. 

 Darwin read an important paper dealing with the mechanical conditions 

 of a swarm of meteorites from a mathematical standpoint. 



SOLAR SYSTEM. 



Motion of the solar system in space. — Dr. Ludwig Struve has made a 

 careful comparison of the Pulkowa catalogues for 1855 with Auwer's 

 re-reduction of Bradley (epoch 1755), and, as one of his results, has ob- 

 tained a value of the motion of our system to which a good deal of in- 

 terest attaches. As it was necessary to assume some connection be- 

 tween the magnitude of a star and its distance, he adopted the follow- 

 ing relative scale, regarding a star of the sixth magnitude as at the dis- 

 tance unity : 



The result he obtains— 4."3G — is then the angular motion of the sun 

 in one hundred years, as seen from the average sixth magnitude star. 

 The actual velocity corresponding to this is about 13 miles per second. 

 The point in the sky towards which the sun is moving is in the coustel- 



