THE AUTHOR'S THEORY OF THE TIDES 205 



an erect position, or that oil, though possessed of weight, 

 will float on water, or that an inflated balloon will 

 rise away from the earth that attracts it, or that a ball 

 of dough will flatten into a thin layer. The circumstances 

 in each case control, and our judgment must guide us in 

 making our interpretations. Before leaving this subject, 

 however, I deem it proper to forestall one possible mis- 

 conception. I do not wish to be understood as implying 

 that any representative fractional part of the mercury- 

 water sphere would possess a hemispherical shape at the 

 moment of collision. On the contrary, each such frac- 

 tional part at the crisis mentioned should be similar in 

 form to a symmetrical part of like mass already incor- 

 porated in the equilibrated unit. 



In holding that comets are intruders into our solar 

 system I am knowingly opposing the latest teaching of 

 the astronomical fraternity. They used to tell us, only 

 a few years ago, that some comets were indigenous and 

 others not, basing conclusions on whether their res- 

 pective orbits were elliptic or hyperbolic. Now they 

 tell us that all of them have their origins within the 

 system, because, forsooth, later mathematical investiga- 

 tions have shown that the hyperbolic curve may be pro- 

 duced by the perturbations of the planets. 



But mathematics is only one phase of this many- 

 sided problem. It lacks correlating virtue. It throws no 

 light whatsoever on how comets come into existence, on 

 their relative ages, on their chemical constitutions, on 

 how they acquired their translatory motions, on why their 

 orbits are so elongated as compared with those of the 

 planets, on the reasons for their usually high inclinations, 

 on why some are retrograde and others direct, on their 

 relation to the asteroids, etc. 



REMARKABLE COMETS 



In order to appreciate the interpretive value of the 

 principles just elucidated, the reader should compare the 

 descriptions of past comets given in such books as Flam- 

 marion's Popular Astronomy. Take, for example, the 



