480 
December 22, and January 12, he assigned to the body 
a parabolic orbit. But he was not satisfied with the 
accordance between this path and the observed motions 
of the body. When he attempted to account for the 
motions of the comet by means of an orbit of comparatively 
short period, he was struck by the resemblance between 
the path thus deduced and that of Comet I, 1805. 
Gradually the idea dawned upon him that a new era was 
opening for science. Hitherto the only periodical comets 
which had been discovered, had travelled in orbits extending 
far out into space beyond the paths of the most distant 
known planets. But now Encke saw reason to believe 
that he had to deal with a comet travelling within the 
orbit of Jupiter. On February 5, he wrote to the eminent 
mathematician, Gauss, pointing out the results of his 
inquiries, and saying that he only waited for the encourage- 
ment and authority of his former teacher, to prosecute his 
researches to the end towards which they already seemed 
to point. Gauss, in reply, not only encouraged Encke to 
proceed, but counselled him as to the course he should 
pursue. The result we all know. Encke showed conclu- 
sively that the newly discovered comet travels in a path of 
short period, and that it had already made its appearance 
several times in our neighbourhood. 
From the date of this discovery, Encke took high rank 
among the astronomers of Europe. His subsequent 
labours by no means fel! short of the promise which this, 
his first notable achievement, had afforded. If, as an 
astronomical observer, he effected less than many of his 
contemporaries, he was surpassed by few as a manipulator 
of those abstruse formule by which the planetary pertur- 
bations are calculated. It was to the confidence engendered 
by this skill that we owe his celebrated discovery of the 
acceleration of the motion of the comet mentioned above. 
Assured that he had rightly estimated the disturbances to 
which the comet is subjected, he was able to pronounce 
confidently that some cause continually (though all but 
imperceptibly) impedes the passage of this body through 
space, and so, by one of those strange relations which the 
student of astronomy is familiar with, the continually 
retarded comet travels ever more swiftly along a continually 
diminishing orbit. 
Bruhns’ life of Encke is well worth reading, not only by 
those who are interested in Encke’s fame and work as an 
astronomer, but by the general reader. Encke the man is 
presented to our view, as well as Encke the astronomer. 
With loving pains the pupil of the great astronomer handles 
the theme he has selected. The boyhood of Encke, his 
studies, his soldier life in the great uprising against Napo- 
leon in 1813, and his work at the Seeberge Observatory ; 
his labours on comets and asteroids; his investigations on 
the transits of 1761 and 1769; his life as an academician, 
and as director of an important observatory ; his orations 
at festival and funeral; and lastly, his illness and death, 
are described in these pages by one who held Encke in 
grateful remembrance as “teacher and master,” and as 
“a fatherly friend.” 
Not the least interesting feature of the work is the 
correspondence introduced into its pages. We find Encke 
in communication with Humboldt, with Bessel and Struve, 
with Hansen, Olbers, and Argelander ; with a host, in fine, 
of living as well as of departed men of science. 
R. A, PROCTOR 
PASM ON SIS, 
[March 10, 1870 
OUR BOOK SHELF 
Elementary Introduction to Physiological Science. 
don : Jarrold and Sons.) 
ANY one may teach the higher branches of science ; none 
but masters should dare to give elementary instruction. 
The truth of this fundamental article of the teacher's 
creed is very strikingly confirmed by this little book, which 
professes to give uninstructed persons some elementary 
knowledge—first, of the chief chemical products of animal 
and vegetable life; secondly, of vegetable physiology ; 
and lastly, of animal physiology. One of the rules of 
teaching which a real teacher has soonest and most 
forcibly brought home to him says, “ Never use an illus- 
tration if you can do as well without it.” The practice 
of the author of this work is evidently, “ Never miss a 
chance of using a metaphor, or simile, or image, or 
illustration that occurs to you. If it is ‘striking’ or 
‘homely,’ use it as often as you can.” The author possibly 
understands his subject ; we cannot tell for certain whether 
he does or no, for we cannot disentangle the real things 
from his striking illustrations of them. We never know 
whether he is speaking soberly or in metaphor, and we 
are perfectly sure that a lad of lively imagination, reading 
this book by way of an introduction to biology, would get 
into his head such fearful and vivid ideas of what was 
going on inside plants and animals, that no subsequent 
teaching could ever set him right, and life would ever 
afterwards be a burden to him, 
Compendium der Physiologie des Menschen. 
Julius Budge. Zweite Auflage. (Leipzig: 
London : Williams and Norgate.) 
VERY truly called a compendium, an account of as many 
as possible of the facts of human physiology being com- 
pressed into about three or four hundred pages. To a 
reader ignorant of physiology, the book would probably 
be wholly unintelligible ; to a German student about to 
undergo an examination in physiology, it would doubtless 
be very acceptable, for by it he might refresh his memory 
on every point about which he is likely to be questioned. 
Perhaps after all, however, it is well for the English 
student that we have nothing like it in the English language. 
The author, in the second edition, has done his best to 
bring the work up to the level of the most recent know- 
ledge. Unfortunately, however, science will not stop 
while an author is correcting proofs; and this, like all 
works professing to give the latest results, records not the 
ultimate but the penultimate researches. This is not, 
however, of very great importance ; for, as in so many Ger- 
man physiological investigations the ultimate result is 
the exact opposite of the penultimate, it is very easy to 
calculate out the former from the latter, and add it on. 
Chenes de l’Amerique Tropicale.— /conographie des 
Espices nouvelles ou peu connues. Ouvrage posthume 
de F. M. Liebmann, achevé et augmenté @un apercu 
sur la Classification des Chénes en général, par A. S. 
Oersted. Copenhagen, 1868. 1 vol. folio, 29 pp. 
Tabb. 57. 
LIEBMANN was occupied at the time of his decease in 
1856 with a monograph of the American Oaks. He left 
behind him a number of folio copper-plate engravings 
which he intended for the illustration of his work, and 
brief descriptions of fifty-two new species. These were en- 
trusted for publication to Prof. Oersted, who has put all in 
proper train, drawn up a valuable essay on the classifica- 
tory characters of the genus, prepared an analysis of many 
of the species, and added ten plates of leaves of various 
species of oak in physiotype,—making altogether an 
important contribution to illustrated botanical literature, 
and a worthy memento of his friend. Liebmann died 
comparatively young, about thirteen years after returning 
from his botanical expedition in Mexico, where he amassed 
very fine collections, which are still in course of deter- 
mination and distribution by the Danish botanists. A 
(Lon- 
Von Prof. 
Gunther. 
