SCIENCE. 
287 
Besides the seasonal variations, there was a gradual 
lowering of the temperature which produced the phenomena 
known as Glacial, and which characterized the Glacial pe- 
riod, as it is generally termed. The appearance of man at 
this stage may be conveniently studied from the point of 
view of the river deposits of Crayford, in Kent, a place re- 
markable for the large number of mammoths, bisons and 
horses, which have there been exhumed. Numerous flint 
splinters of unmistakeable human workmanship were dis- 
covered in the Spring of the present year, under conditions 
which indicated the exact spot on which an ancient hunter 
sat and chipped them, and these chips being so little dis- 
turbed that it was found possible to put together several 
large masses, and to restore some of the original nodules 
from which the implements were made. In one case I 
was fortunate enough to discover an implement rudely 
chipped all around which indicated that the primeval 
hunter of the mammoths, bisons and horses of that neigh- 
borhood was in the same state of culture as the man 
who hunted reindeer in the valley of the Thames in the 
next or the latest stage of the Pleistocene period. The river 
valleys of the south of England are covered with sheets of 
gravel termed river drift, and these contain vast numbers of 
rein'deer, as well as bisons and horses, and were accumu- 
lated at a time when the climate was severe. In these, nu- 
merous implements were discovered, extending from Peter- 
borough, in the north, as far as the channel. Similar imple- 
ments are also met with in France, and occur n Spain, 
Italy, Greece, Northern Africa, and Egypt ; they also occur 
in Asia Minor, and have been found throughout the penin- 
sula of India. They indicate a primeval condition of sa- 
vagery from which mankind has emerged, which was uni- 
form over the whole of this area. It is not a little strange 
that the river-drift hunter should have used implements of 
precisely the same shape and material in the Indian jungles, 
in the forest-clad shores of the Mediterranean, and in the 
wilds of Middle and Northern Europe. No human remains 
assignable to this age are sufficiently perfect to allow of our 
passing opinion of man’s physique, but they tell us that he 
was a man and not a “ missing link.” The researches of 
Dr. Abbott on the river gravels of Trenton appear to esta- 
blish the fact that the river-drift man was an inhabitant of 
America during the time when the mammoth was living in 
the valley of the Delaware. The paleolithic implements of 
the ate Pleistocene river beds are rude and simple, although 
they show a considerable advance from the simple flake, 
which is the only trace left by the man of the middle Pleis- 
tocene. As regards the man of that period, it is probable 
that the plateau of Central Asia was the centre from which 
the race diverged. 
On the bottom of the caves of Creswell, in Yorkshire, 
were found river-drift implements in association with vast 
numbers of gnawed bones of both living and extinct ani- 
mals, brought in by hyenas, while in the upper portions 
were found implements of a higher type, composed of flint 
and carved bone. Among these was the incised figure of a 
horse ; these imply a higher type than that of the river- 
drift, and belong to a state of culture known as that of the 
cave man. It seems to be unquestionable that the cave 
men were preceded in their habitations by the river-drift 
men, in some places at least, and that of the two sets of im- 
plements now found the ruder belongs to the latter race. 
It has been a debated question whether the civilization of 
the cave man was the outcome of the development of that 
of the river-drift man. The evidence seems to indicate that 
they must be classed either as two distinct races or as two 
sections of the same race, which found their way into 
Europe at widely different times — the river-drift men being 
of far greater antiquity in Europe than the others. The 
discoveries of late years tend to confirm the identification of 
the cave men with the Esquimaux. We infer that the cave 
men clothed themselves with skins, for instruments for 
dressing skins are found precisely like those now employed 
for that purpose by the Esquimaux. That they wore gloves 
is shown by carvings which represent them, and there is 
reason to believe that they were in the habit of decorating 
their persons in various ways. The art of representing 
wild animals in carvings and by sculpture was carried to a 
high stage of excellence by the cave-dwellers, and it is 
doubtful if an artist of the present time could do better 
work, or even as good, with the rude instruments used by 
them. One of the most interesting examples of their skill 
is shown by representation of a mammoth, and we know 
that the extinct creature is faithfully por-trayed, because 
its remains have come down to us perfectly preserved in 
the ice of the northern latitudes. In various ways the 
habits of the cave men correspond to those which now 
prevail among the Esquimaux. 
NATURAL SELECTION. 
A curious instance has occurred showing the difficulty 
of explaining the true theory of “ Natural Selection,” 
even to scientific men ; it is therefore not surprising to find 
that those who are opposed to the principle from religious 
motives, fail to realize what is understood by the term. 
In a letter to Nature , Mr. Charles Darwin states he is 
sorry to find Sir Wyville Thompson does not understand 
this principle of natural selection as explained by himself 
and Dr. Wallace, as, if he had done so, he would not have 
wrttten a sentence found in his introduction to the voyage 
of the Challenger, as follows ; “ The character of the 
abyssal fauna refuses to give the least support to the 
theory which refers to the evolution of species to extreme 
variation, guided only by natural selection.” This, says 
Mr, Darwin, is a standard of criticism not uncommonly 
reached by theologians and metaphysicians, when they 
write on scientific subjects, and asks, “ can Sir Wyville 
Thompson name any one who has said that the evolution 
of species depends only on natural selection ?” and con- 
tinues, “ as far as concerns myself, I believe no one has 
brought forward so many observations on the effect of the 
use and disuse of parts, as I have done in my ‘ Variations 
of Animals and Plants under Domestication,’ and those 
observations were made for that special object. I have 
also there adduced a considerable body of facts, showing 
the direct action of external conditions on organisms, 
though, no doubt, since my books were published, much 
has been learnt on this head.” 
PROPAGATION OF SOUND BY LIGHT IN 1811. 
In searching a volume, dated 1811, for papers relating 
to the introduction of illuminating gas, we noticed a paper 
by Modeste Parolette, entitled “ Inquiries Concerning the 
Influence of Light on the Propagation of Sound,” taken 
from the Journal de Physique, Vol. LXVI1I. 
Although Parolette cannot be said to have anticipated 
those physical facts, the knowledge of which enabled 
Edison to design that wonderful instrument, the 
Tasimeter, and since developed by Bell in his Photophone, 
still Parolette seemed to be on the right track. 
In opening his subject, Parolette states that the object of 
his inquiry was the relation which subsists between the 
action of light and the vibrations of sonorous bodies, 
and he actually made an instrument for measuring the 
effect of light on sound-vibrations, and called it the Pho- 
nometer. 
Parolette’s experiments were rude compared with those 
of more recent date, but it most be remembered that they 
were made seventy years ago. He used no mirrors for con- 
centrating a beam of light, but relied merely on the 
natural properties of light without such aids. He says, 
“As it is known that the vibrations of elastic fluids are 
always analogous to those of the particles of the sounding 
body, and that if two strings, belonging to two instru- 
ments. be in unison, when one is touched the other will 
vibrate and emit a perceptible sound ; I availed myself 
of these properties in the construction of my apparatus, 
and in determining the object of my inquiry. 
The Phonometer consisted of two violins placed on a 
horizontal plank ten feet long and eight inches wide. Hav- 
ing tuned these instruments to the Paris diapason, he fixed 
a piece of paper to the second string of one of them to 
