APRIL 25, 1884.] 
Rhythmic variation. 
It is a general axiom in ‘breeding’ and in allied 
biological discussions, that ‘like produces like;’ and 
yet in nature, or under art, we have no instance we 
can use where like has produced an identical likeness. 
It rather seems that the practical expression should 
be the converse one, that ‘variation produces varia- 
tion;’ for in nature we find variation the general fact, 
no animal and no plant producing offspring pre- 
cisely similar to itself. Indeed, as the attribute of 
life is motion and but momentary equilibrium be- 
tween internal and external forces, we may consider 
variation as an empirical law of nature, and as in- 
fluenced by the law of rhythm, as outlined by Herbert 
Spencer, who says that rhythm results wherever there 
is a conflict of forces not in equilibrium. 
This law of rhythm seems sufficient to explain, in 
part or in whole, some of the variations observed 
in species, and for which neither natural nor sexual 
selection can account. Given organisms under 
similar environment, and remote from selective op- 
portunity, we must believe that variations must 
occur; and these variations must naturally become 
grouped about types under the action of heredity and 
some other general laws, giving through rhythmic 
action the appearance of progressive development. 
Probably this law of rhythmic movement may ex- 
plain the interesting variations which have origi- 
nated species in certain protoplasmic organisms, as so 
well described by Professor Asa Gray (Amer. journ. 
sc., April, 1884, 327), who says, — 
** No exercise of ‘ natural selection’ could produce the succes- 
sive changes presented in the evolutionary history of the typical 
Orbitolites, from Cornospira to Spiroloculina, from Spiroloculina 
to Peneroplis, from Peneroplis to Orbiculina, from Orbiculina to 
the ‘simple’ forms of Orbitolites, and from the ‘simple’ to the 
“ complex’ forms of the last-namedtype. And as all these earlier 
forms still flourish under conditions which (so far as can be as- 
certained) are precisely the same, there is no ground to believe 
that any one of them is better fitted to survive than another. 
They all imbibe their nourishment in the same mode, and no 
one type has more power of going in search of it than another. 
That they are all dependent on essentially the same conditions 
of temperature and depth of water, is shown by their occurrence 
in the same marine areas. That they all equally serve as food to 
larger marine animals, can scarcely be doubted; and itis hardly 
conceivable that any of their devourers would discriminate (for 
example) between the disks of a large O. marginalis, or middle- 
sized O. duplex, and a small O. complanata, which even the trained 
eye of the naturalist cannot distinguish without the assistance 
of a magnifying-glass.” 
E. LEWIS STURTEVANT. 
Geneva, N.Y., April 12. 
Rare Vermont birds. 
In a list of birds given under this heading in No. 
55 of Science, appeared the American avocet (Recur- 
virostra americana Gm.) and orange-crowned warbler 
(Helminthophaga celata Say, Bd.). It appears, these 
were admitted on mistaken evidence, and are not to 
be considered as Vermont birds. 
FRANCIS H. HERRICK. 
THE APRIL SESSION OF THE NATIONAL 
ACADEMY OF SCIENCES. 
Tue number of papers presented at the ses- 
sion of the National academy of sciences in 
Washington last week was less than usual, 
and, judging from the discussions, none were 
of commanding interest and importance. An 
unusual number of prominent members were 
absent from the meeting ; and it also happened 
SCIENCE. 
903 
that the social re-unions which have usually 
accompanied the annual session were, from 
various accidental circumstances, omitted. It 
has long been a custom, if not an unwritten 
law, of the academy, to decline all social at- 
tentions which do not come either from mem- 
bers or officers of the academy, or from heads 
of government departments interested in its 
work. 
An interesting feature of the meeting was 
a communication received from Mrs. J. Law- 
rence Smith, widow of the late lamented 
chemist of Louisville, proposing to give the 
sum of eight thousand dollars, which she had 
received from Harvard college by the sale of 
Professor Smith’s collection of meteorites, to 
establish a memorial fund for the promotion 
of meteoric research. The academy will then 
have four considerable funds for the promotion 
of science, — the Bache, Draper, Watson, and 
Smith funds. 
The following were some of the more inter- 
esting of the physical papers : — 
It has long been a well-known result of 
theoretical mechanics, that the rotation of the 
earth causes a slight tendency in any south- 
ward-flowing river of the northern hemisphere 
to press towards its right bank; and various 
phenomena have been attributed to this, 
among others a supposed tendency of drift- 
wood to accumulate on the right rather than 
on the left bank. It is, however, readily 
shown that this tendency could not produce 
this effect; and the general conclusion has 
been, that the only effect would be an imper- 
ceptible difference of level of the two sides of 
the river. The object of the first paper read — 
that of Mr. Gilbert, on the deflection of river- 
courses in consequence of terrestrial rotation — 
was to point out an indirect result of the forces 
in question, which had hitherto been over- 
looked, and which might produce observable 
results. He showed that the effect of terres- 
trial rotation is to increase the centrifugal 
force on those curves which deflect the river 
from the right towards the left, and to dimin- 
ish the force in the opposite direction; the 
difference in the case of the Mississippi River. 
being about one-tenth part of the whole. 
In his paper on the origin of crystalline 
rocks, Dr. Sterry Hunt conceived that rocks, 
like gneiss and other felspathic, hornblendic, 
and quartzose aggregates, resulted from the 
action of water on the superficial and last con- 
gealed part of the earth’s crust, through up- 
ward lixiviation. The separation of zeolites 
and quartz from basic rocks is a survival of this 
process of deposition from mineral springs, 
