406 Drs. G. J. Stoney and A. M. W. Downing. 



shall be of moderate length. Through one of these, which we may call 

 segment A, the earth passed in November, 1866, and on that occasion 

 there was withdrawn from it that small portion which consisted of 

 meteors which either encountered or passed close to the earth. Those 

 that actually plunged into the earth's atmosphere were destroyed : 

 those that passed near were deflected, and were also either accelerated 

 or retarded, and they thus became clino-Leonids. It is with the great 

 majority of the meteors in segment A, which escaped both these fates 

 and continued to be ortho-Leonids, that Adams's investigation is con- 

 cerned. He ascertained their orbit ; and starting from the elements of 

 the orbit as determined by him, the actual perturbations which it has 

 since undergone have been computed, and the main results thus arrived 

 at are embodied in the following table. 



As already stated, the calculation has been extended over an entire 

 revolution of that portion of the stream which we have called seg- 

 ment A and in computing the perturbations, account has been taken 

 of the attraction exercised upon these meteors by Mars, Jupiter, 

 Saturn, and Uranus. At first Yenus and the Earth were included, 

 but as the influence of these planets was found to be insensible, they 

 were omitted from the latter part of the calculation. 



The expense of carrying on the work has been met partly out of the 

 Government Grant administered by the Royal Society, and partly out 

 of the Eoyal Society's Donation Fund. The computations have been 

 made by Messrs. F. B. Cooper, J. H. Bell, and W. H. Walmsley, 

 members of the staff of the Nautical Almanac office. We are also 

 indebted to Mr. E. Eoberts, the chief assistant, for his aid in various 

 parts of the work. The method adopted was that by mechanical 

 quadratures, the determinations of the variations of the elements being 

 made at intervals of thirty-six days, except for the period from May, 

 1871, to December, 1894, during which time the perturbations were 

 small and progressed so regularly that it was found sufficient to make 

 the computations at intervals of 216 days. 



The most noteworthy features are a near approach to Saturn in April, 

 1870, and a near approach to Jupiter in August, 1898, at which 

 latter time the meteors in segment A of the stream were at a distance 

 from the planet of only 0*9 of the mean radius of the earth's orbit. 

 The consequences of these near approaches are brought out in the 

 table. Uranus produced but little .effect in this revolution. The 

 planet was at a distance when the swarm crossed his orbit. And the 

 influence of Mars was trifling. So that nearly the whole of the per- 

 turbations during this revolution have been caused by Jupiter and 

 Saturn. 



