L. Page — A Century's Progress in Physics. 305 



larly at intervals of seventy-six years ; the last appear- 

 ance in the spring of 1910 is no doubt well remembered 

 by the reader. Kant had considered comets to be 

 formed by condensing solar nebulae, whereas Laplace had 

 maintained that they originate in matter which is scat- 

 tered throughout stellar space and has no connection 

 with the solar system. A study of the distribution of 

 inclinations of comet orbits by H. A. Newton (16, 165, 

 1878) of New Haven substantiated Laplace's hypothesis, 

 and led to the conclusion that the periodic comets have 

 been captured by the attraction of those planets near to 

 which they have passed. Of these comets a number 

 have comparatively short periods, and are found to have 

 orbits which are in general only slightly inclined to those 

 of the planets, and are traversed in the same direction. 

 Moreover, the fact that the orbit of each of these comets 

 comes very close to that of Jupiter made it seem probable 

 that they have been attached to the solar system by the 

 attraction of this planet. Further confirmation of this 

 hypothesis was furnished by H. A. Newton's (42, 183 and 

 482, 1891) explanation of the small inclination of their 

 orbits and the scarcity of retrograde motions among 

 them. 



In 1833 occurred one of the greatest meteoric showers 

 of history. Olmstead (26, 132, 1834) and Twining (26, 

 320, 1834) of New Haven noticed that these shooting 

 stars traverse parallel paths, and were the first to sug- 

 gest that they must be moving in swarms in a permanent 

 orbit. From an examination of all accessible records, 

 H. A. Newton (37, 377, 1864; 38, 53, 1864) was able to 

 show that meteoric showers are common in November, 

 and of particular intensity at intervals of 33 or 34 years. 

 He confidently predicted a great shower for Nov. 13th, 

 1866, which not only actually occurred but was followed 

 by another a year later, showing that the meteoric swarm 

 extended so far as to require two years to cross the 

 earth's orbit, H. A. Newton (36, 1, 1888) in America 

 and Adams in England took up the study of meteoric 

 orbits with great interest, and the former concluded that 

 these orbits are in every sense similar to those of the 

 periodic comets, implying that a swarm of meteors 

 originates in the disintegration of a comet. In fact 

 Schiaparelli actually identified the orbit of the Perseids, 

 or August meteors, with Tuttle's comet of 1862, and 



