396 KANSAS CITY REVIEW OF SCIENCE. 



and it is lengthened enormously or lost entirely within a few days, which could not 

 be from any other than an optical cause. 



Comets, we are told, have been calculated as to their orbits, but we have the 

 additional fact that no return of a calculated comet has ever been known to ap- 

 pear under the same circumstances, a fact that suggests of itself that they are not 

 within the solar system, either in whole or in part, but that it is the position of 

 the bodies composing the solar system and their spheres to that of the observer 

 on the earth that controls the phenomena attending the appearance of comets. 

 In fact, when we consider that comets are without the solar system and obeying 

 the laws of another system entirely beyond ours, about which we cannot know 

 anything, the presumption is very strong that observers mistake comets that come 

 at or within a few years of calcultated periods for the expected return. There can 

 be no certainty, even if we admit that comets do sometimes enter the solar sys- 

 tem and leave it again, for in the infinitude of worlds and systems they must 

 traverse on such theory, we cannot discount the forces with^ which they come in 

 contact to retard or accelerate their motion or deflect them from the imaginary 

 orbits we prescribe for them. At best the whole comet lore of our astronomers 

 is conjectural — guess work and unreliable — and every one is at Hberty, as we are, 

 to have a theory of his own. 



There is a theory, admitted by all astronomers, which may account for 

 comets, and coincides with the assumption that they are outside the solar system. 

 It is that our system is but one of thousands of suns and their families, all mov- 

 ing around their central body in the same plane. These systems of suns in their 

 circles of motion must frequently come in contact or close conjunction, and the 

 comets belonging to them become visible or approach so near the attractive 

 force of our system as to be influenced in their movements by it. These sister 

 systems may not all be in the advanced state of planetary evolution that we are, 

 and these comets, numbering thousands, be visible thousands of years, as the sys- 

 tems to which they belong and that to which we belong are performing their evo- 

 lutions. 



That the theory we have here outlined has facts to support it we need only 

 refer to the appearance of Halley's comet in 1835, The comet was visible for 

 nine months from the earth. Its first appearance was without a tail for two 

 months, when a tail began to appear, and rapidly developed until it was twenty 

 degrees in length. It then began to shorten, and in twenty days it entirely dis- 

 appeared. After its "perihelion" it disappeared for two months. On its reap- 

 pearance it had no vestige of a tail, and the nucleus appeared surrounded by a 

 coma. As the comet receded from the Sun it increased rapidly in dimensions, 

 until in one week it was forty times its size the previous week. It continued to 

 increase until it actually became invisible from expansion, all except the nucleus, 

 which increased in brightness as the envelope dilated and disappeared. At its 

 very last observation it appeared as when first seen — a small round nebula with a 

 bright point in the center. Can any theory so well account for these rapid 

 changes of appearance as the optical one we have alluded to, and which will be 



