The Theory of Encke's Comet. 

 BY G. R. SMALLEY, ESQ. 



[Eead August 2nd, 186-5.] 



BEFOBE entering upon the subject of my present paper, I must 

 express my hope that you have not prepared yourselves for any 

 brilliant discovery, or the advancement of any new theory. It 

 is not intended to enter upon any speculation as to the Physical 

 Structure of Comets generally a subject, beyond all others, 

 deficient in data. My object on the present occasion is to find 

 out by an examination of certain familiar facts, "What is the 

 use of Encke's Comet, rather than what it is made of." 



Encke's Comet, though bearing the name of that eminent 

 Astronomer, is also known as " Pons' Comet," from Pons, who 

 discovered it in 1805, and again in 1819 ; but there is no doubt 

 that this same Comet had been previously seen in 1786, and 

 again in 1795. Encke indeed, though he always refers to it as 

 Pons' Comet, pointed out the identity of the object observed On 

 these four occasions ; made it his intense study, and predicted its 

 return in 1822. It was true to its appointment, and, which 

 makes it an object of some local interest, its re-appearance was 

 observed in that year by Rumker, at Sir Thomas Brisbane's 

 Observatory, at Paramatta, Justly then has it acquired its 

 usual title from Professor Encke, who devoted twelve years of 

 arduous labour to its discussion, and not only predicted its future 

 appearances, but established the important proposition to which 

 I shall draw your attention this evening. 



These " Hairy Stars," as they have been termed wandering 

 vapours, it may be that appear in our system for a brief 

 period, when most of them launch into the immensity of space, 

 and " no man sees them more," were, in the darker ages, objects 

 of superstitious veneration : and even in more enlightened times 

 they appear to excite in many minds, not only a romantic 



