12 John Francis Encke. 
sier in 1786, and again with the comet discovered by Miss Her- 
schel in 179%, and with the comet of Pons in 1805. The result of 
his investigations was, that this comet, which astronomers have 
agreed to designate as “ Encke’s Comet.” (although he himself 
always modestly calls it the Comet of Pons), would make its ap- 
penance again in 1822, although it would not then be visible in 
urope. Accordingly our Society had the gratification of pre- 
senting to Mr. Riimker their medal for its discovery at Para- 
matta in 1822, on the same oe when they bestowed a similar 
mark of approbation, as we have already stated, on Encke him- 
self, for its rng 
as in these Memoirs, that Encke signalized himself by his 
systematic and most successful application of the principle of least 
squares to a number of astronomical observations. For the meth- 
od itself we are mainly indebted to Legendre and to Gauss, but 
for the first exhibition of its vast practical value, we are indebted 
to the example of Encke. His mind, indeed, seems to have 
en preéminently arithmetical, delighting in the orderly and 
systematic development of what otherwise and to many would 
seem an inextricable maze of figures. Those who knew 
best consider that he probably injured the generality of his math- 
ematical analysis by the fastidious care which he bestowed upon 
its symmetrical arrangement. 
In 1825, at the recommendation of Bessel, Encke was appointed 
to the Directorship of the Observatory at ‘Berlin; the Observa- 
tory itself was both improperly situated, and inadequately sup- 
lied with instruments, but ultimately, at the suggestion of Hum- 
oldt, a new Observatory was erected at the expense of the Prus- 
sian government, Encke maperiniondine personally both its con- 
struction and its interior arrangements. And here, for eight or 
ears after its completion, he conti nued with much assiduity 
pes observe both with the Transit Circle and the Equatorial; but 
his natural tastes did not lie in instrumental Spam and 
after the discovery of numerous small planets by variou observ 
ers, he devoted himself with much success to the caved gation 
of olanetary disturbane 
labors of Eneke { in reference to the comet which bears 
his name have already been referred to. Having carefully taken 
into account the perturbing action of the planets on this comet 
during several successive periods, he established the remarkable 
fact that there is some extraneous cause in operation which con- 
tinually diminishes the comet’s periodic time. This is evidently 
the effect which would be produced if the comet suffered a re- 
sistance — moving in a very rare ethereal medium, and accord- 
ingly this is the explanation proposed by Encke, and at present 
aaaeally aces by astronomers. 
