THE STELLAR UNIVERSE. 



The solar system is supplied with feelers, which it is enabled to 

 throw out into the regions surrounding it to vast distances, and these 

 are endowed with the highest conceivable susceptibility, which 

 would cause them to betray to us the presence in these regions 

 even of masses of matter of very limited dimensions. These 

 feelers are the COMETS, and in particular one called Halley's comet. 

 This body emerges periodically, and makes an excursion into the 

 surrounding regions to a distance of little less than one thousand 

 millions of miles beyond the limits of our system, and returns at 

 regular intervals to the sun. It is a body of extreme levity 

 and tenuity compared even with the smallest planetary masses ; 

 it is, therefore, eminently susceptible of the effects of gravitation 

 proceeding from a body external to it. 



We shall show, on another occasion, that when this body, once 

 in seventy-five years, departs from our system to make its vast 

 excursion through distant regions of space, the eye of science 

 pursues it along its path, watches its movements, and follows its 

 course. That course is calculated upon the supposition that it is 

 subject to no attraction through the entire range of its orbit 

 except those of the sun and planets, and the calculations of its 

 return are thus made. The time and the place of each of its 

 successive returns have been foretold; and we have found that 

 they have corresponded faithfully with such predictions. It is 

 certain, then, that in its range through space this body has not 

 passed in the neighbourhood of any mass of matter capable of 

 exercising an observable attraction upon it. In fact, it moves 

 exactly as it would move if no material object existed in the 

 creation save those of the solar system itself. It follows, therefore, 

 that all other objects must be too distant from our system to pro- 

 duce any discoverable attraction even on so light a body as this. 



6. Yet when, on any clear night, we contemplate the firma- 

 ment, and behold the countless multitude of objects that sparkle 

 upon it, remembering what a comparatively small number are 

 comprised among those of the solar system, and even of these 

 how few are visible at any one time, we are naturally impelled 

 to the inquiry, Where in the universe are these vast numbers of 

 objects placed ? 



Very little reflection and reasoning, applied to the consideration 

 of our own position and to the appearance of the heavens, will 

 convince us that the objects that chiefly appear on the firmament 

 must be at almost immeasurable distances. The earth in its 

 annual course round the sun moves in a circle, the diameter of 

 which is about two hundred millions of miles. We, who observe 

 the heavens, are transported upon it round that vast circle. The 

 station from which we observe the universe at one period of the 

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