﻿NATURE OF THE TEMPORARY STAR OF 1572. 315 



seventeen months out of more than three hundred years; and 2d. That a uniform 

 rate of rotation should produce a uniform interval between the apparitions of the 

 star. 



Keill and Pigott adopted a period of about one hundred and fifty years for the 

 star, instead of three hundred, which Arago says, " without raising new difficulties, 

 has the advantage of assimilating the period somewhat to those of the other variable 

 stars."* • 



It is not easy to coincide here with the great French astronomer, for a question 

 which instantly arises, viz. : why was not the star seen in 1095, 1414 and 1722 ? 

 cannot be answered. 



We have now examined the views of the most eminent writers upon the subject 

 of this wonderful star, from the period of its apparition to the present time, but 

 unfortunately the hypotheses which are sufficient to explain the cause of its sudden 

 appearance and subsequent extinguishment have not the support of analogy ; and 

 the theories which have been based upon conditions known to exist are not sufficient 

 to explain the phenomena. 



Let us now ask, may we not learn some important truths with regard to this star, 

 by a direct interrogation of nature ? Surely the well established laws of motion can 

 yield us some light. 



Let us first inquire, does this body move ? 



In view of the universal distribution of matter, rest is an astronomical impossibility. 

 It may therefore be confidently affirmed that the star of 1572 does move. 



If it move, does it do so in a straight line ? 



The distribution of matter would compel a negative answer to this enquiry. 



What, then, is the nature of its motion ? 



Our acquaintance with the movements of the heavenly bodies permits but one 

 answer to this question, viz. : that the star moves in one of the conic sections, about 

 a point which is a focus common to it and some other body of space. 



Thus far do we advance under the guidance of inexorable necessity. As we pro- 

 gress, we shall discover that we have already obtained data which will account 

 for one of the minor phenomena of the star, for which an explanation has never been 

 proposed. 



As far as the requirements of the views we are about to offer go, it matters not 

 which of the conic sections we assume to be the one in which the star moves ; but for 

 the sake of simplicity, and for convenience of demonstration, we will suppose that it 

 moves in a circle, and that the plane of its orbit is not at right angles with the visual 

 ray connecting it with the earth. 



*Astronomie Populaire, vol. L p. 414. 

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