Fune 9, 1870] 
lives ; he then distinguishes between normal and absclute 
potential activity, and shows that in man alone do these 
two nearly coincide. 
The two chief circumstances which favour longevity 
are high individualism, for this in itself requires time ; and 
small expenditure, the latter embracing the wear and tear 
put forth in the procurement of food and in the reproduc- 
tion of the species. In support of these statements Mr. 
Lankester then adduces a considerable number of the 
more trustworthy observations that have been made in 
reference to the longevity of individuals belonging to 
different classes of the animal kingdom, some of which 
we here append. Our knowledge, it appears from these 
tables, of the duration of life in the lower classes, is very 
imperfect. Amongst the Protozoa, Spomgilla fluviatilis 
dies yearly, leaving gemmules. Amongst the Ccelenterata, 
Hydra viridis reproduces sexually in autumn and then dies. 
An Actinia mesembryanthemum has been living forty- 
two years in an aquarium and is still alive. Amongst 
the Crustacea, some of the larger crabs and lobsters must 
have attained a great age; but Mr. Lankester has 
observed one species, Chetrocephalus diaphanus, which 
developes from the egg, reproduces and dies in from two 
to three months. In the Insecta, the imago, as a rule, 
lives part of a year, from six months to a few hours, dying 
on reproduction, The length of life of the larva varies 
greatly in closely allied forms, from four years or more to 
aweek. Fleas may liveas longasnine months. Scarcely 
any observations have been made on the length of life in 
the molluscoidea and mollusca. Fish appear to have great 
tenacity of life. Thus, the carp is believed to have attained 
the age of 150 years, and the pike 267 years, if a ring with the 
following inscription is genuine—“T am the fish which 
was first of all put into this lake by the hands of the 
Governor of the Universe, Frederick II., the 5th of 
October, 1230.” It weighed 350lbs., and was 19 feet 
long. Its skeleton was exhibited at Mannheim, and 
it was taken at Halibrun in Suabia in 1497. Of the 
Amphibia, the toad lives 36 years, the frog 12 to 16, and 
various tortoises are inferred to be of great age from 
their size. Amongst birds, the parrot, goose, falcon, and 
raven are long-lived, the two former reaching 100 to 120 
years, and the two latter exceeding 150 years. Wrens only 
live two or three years. Amongst mammals, the whale and 
elephant have the longest term of life, both probably 
exceeding 100 years, and possibly reaching 200; horse 
25, but occasionally reaching 40 years ; ox I5 to 20 years ; 
sheep and goat 12 years ; lion 20 to 50 years; cat 9 to 18 
years. 
Mr. Lankester comments on these tolerably well ascer- 
tained facts, and shows how they support the theory that 
longevity depends on the influence of generative and 
personal expenditure. 
The last part of the work is devoted to the longevity 
of man, satisfactory conclusions respecting whom are 
almost limited to the very highly civilised nations. Mr. 
Lankester appears to entertain no doubt that cases have 
occurred where the age of one hundred has been exceeded. 
We have limited ourselves to a brief epitome of the 
contents of Mr. Lankester’s work, and cordially recom- 
mend it to our readers. 
H, POWER 
NATURE 
oo 
OUR BOOK SHELF 
The Fuel of the Sun. By W. Matthieu Williams, F.C.S. 
(London : Simpkin, Marshall, and Co.) 
WE have in the work before us a proof that a very 
interesting and readable volume may be produced, 
although the hypothesis which has called it into being 
may be one with which we do not agree. Mr. Williams 
discusses at great length the very perplexing question of 
the sun’s fuel, nevertheless we do not think that his 
hypothesis is an improvement upon that of Helmholtz 
and Thomson. But let us hear the writer speak for him- 
self. After having come to the conclusion that an atmo- 
sphere very similar to our own, but only more attenuated, 
pervades all space, he supposes that the sun, in its 
progress through space, encounters new portions of this 
atmosphere, and then asks the following question—* Does 
there exist in the actual arrangements of the solar system 
any machinery for stirring in an important quantity of 
the new atmospheric matter and ejecting the old? If so, 
the maintenance of the sun’s heat may be fully accounted 
for.” The question is answered in the affirmative ; the 
atmosphere is supposed to be the sun’s fuel, and the 
planetary attendants of the sun are supposed to perform 
the duty of stokers with untiring vigilance and efficiency. 
The mode of action of this atmospheric fuel in furnishing 
heat is supposed to be as follows :—“ It is evident then 
that the first result of the great evolution of heat from 
mechanical condensation of the mixed atmosphere of 
aqueous vapour, carbonic acid, and free oxygen and 
nitrogen, will be the dissociation of the water and 
the carbonic acid. But there must somewhere be a 
height at which the temperature capable of effecting 
dissociation terminates; where the atmosphere of ele- 
mentary gases fringes upon that of combined aqueous 
vapour, and where these separated gases must revert into 
reunion with a furious chemical energy which will be 
manifested by violent combustion. Thus we shall have a 
sphere of dissociated gases and a sphere of compound 
vapours separated by an interlying stratum of combining 
gases, a spherical shell of flame, constituting exactly what 
solar observers have described as the ‘photosphere.’” In 
fine, Mr. Williams’ hypothesis is “a perpetual bombard- 
ment of 165 millions of millions of tons of matter per 
second without in any degree altering the density, the 
bulk, or any other element of the solar constitution.” 
B. STEWART 
Linlettung in die Physik. Bearbeitet von Professoren G. 
Karsten, F. Harms, und G. Weyer. 
THE volume before us is introductory to the “ Allgemeine 
Encyclopadie der Physik,” which is in course of publica- 
tion, under the general editorship of Professor Karsten. 
The. authors endeavour to supply whatever would not 
naturally be found or expected in the separate treatises 
of which the Encyclopedia is made up, which have been 
written independently by specialist authors from their in- 
dividual points of view. They add a systematic treatment 
of everything that may be considered auxiliary to the 
entire group of the physical sciences. 
Professor Harms is the author of the most important 
part of the work—a philosophical and historical introduc- 
tion to the whole subject. The discussion ranges over 
three principal heads— 
1. What are the proper limits, and the true relations of 
physical science, and what distinctions can be drawn 
between it and the other sciences of matter ? 
2. What are the methods of physical inquiry, with a 
critical estimate of induction, of speculation or deduction, 
and of the theory of cognition (Erkenntniss-theorie) which 
has arisen in Germany since the days of Kant. This dis- 
cussion is naturally conducted both historically and meta- 
physically. The rapid but exhaustive reyiews of Bacon, 
