66 
POPULAE SCIENCE NEWS. 
[May, 1S90. 
of view and poses his sitters without thinking 
of the inverted iiosition in which they appear. 
In 3, however, the conditions are changed. 
The iUiiminated opening in the card acts as 
an independent source of light, and casts the 
shadow of the pin directl}' upon the retina ; 
the head of the pin being smaller than the 
pupil of the eye, and being held so close to it 
that the shadow is cast directly upon the 
retina, without the usual reversal of the 
image, which, therefore, appears to our mjnd 
as upside down, whereas it is really in an 
upright position. This automatic correction 
by the eye or brain of the images thrown 
upon the retina is a curious fact, and cannot 
be said to be fully understood, althougli the 
explanation given above is probabl}' the cor- 
rect one. 
Fig. 4. 
This experiment may be varied in several 
ways. By looking, or "squinting," at the 
opening through the half-closed lids, the re- 
versed shadow of the eyelashes will be per- 
ceived, and, by moving the card quickly before 
the eye, so that the opening describes a small 
circle, the field of vision will appear filled 
with a network of dark lines, which are the 
images of the capillary blood-vessels of the 
retina. As this last experiment is not always 
successful, it should not be persisted in, on 
account of the strain it imposes upon the 
eyes. 
The illustrations accompanying this article 
are reproduced from La Nature. 
[Original in Popular Science News.] 
HOW OLD IS THE WORLD .> 
BY JOSEPH WALLACE. 
The chronology of the birth of the terrestrial 
globe has always been a profound and difficult 
problem to solve. Some attempts, however, have 
been made to arouse the learned to a more liberal 
spirit of inquiry; the theologians had kept within 
what they considered probable bounds, and were 
not disposed to change the established chronology 
until science could offer them a theory free from 
doubts and speculations. 
Eusebius, in the beginning of the fourth century, 
though far from grasping the whole extent of the 
difficulty, questions the limited knowledge of the 
people in regard to the chronology of the world. 
Almost all of the chronologists prior to the present 
century have considered the epoch of the creation of 
the world with that of man, because they believed 
the one was separated from the other only by an 
interval of six days of twenty-four hours each. 
Some brighter minds, however, avoided confound- 
ing the two great events. St. Gregory of Nazianze 
supposed an indefinite period between the creation 
of matter and the first regular organization of life. 
Gennade of Marseille expressed in his Dogmes Eccle- 
siastiques his belief that after the creation of heaven, 
earth, and water, the heavenly hosts could see the 
manifestations of God's power through the long 
spaces of time which should pass yet before the 
days of creation. 
Although many of the early Christian theologians 
and philosophers were little disposed to raise objec- 
tions against the authority of the Bible, yet they 
felt themselves embarrassed by the short duration 
of time which passed between the deluge of Noah 
and the period assigned to the creation of the world. 
Still they could not accept the fabulous stories ad- 
duced by ancient writers, who mentioned mytholog- 
ical tniditionsof Tridians, Centaurs, etc., before the 
creation of the human race. Still among these tm- 
ditions there is a source of evidence pointing back 
to a period of antiquity too remote to be reconciled 
with the short chronology of Usher and Petrie. Of 
course it is now the almost universal accord of 
Christian theologians that long periods of time 
must have elapsed prior to sacred history. 
In 16S7 the learned Jesuit, P. Pezron, wrote : 
"The antiquity of the times is a good deal greater 
as one believes today." He defended this new 
hypothesis against the attacks of Martianay and 
Leguien with great learning and skill, though at 
that early day it was conflicting with the general 
opinion of the fathers and early Christian philoso- 
phers and scientists, who counted about 4,000 years 
until the coming of the Messiah. This chronology 
was based on the historic records of the Chaldeans, 
Egyptians, and Chinese, though differing from the 
actual Hebrew text. 
Thirty-two years after, another eminent Jesuit, P. 
Tournemine, spoke in the same sense ; "The Jew- 
ish calculation appeared to me always too short and 
little in agreement with certain monuijients of his- 
tory, especially what concerns the epoch which fol- 
lowed the deluge. It takes off to the chronologists 
several necessary centuries for the agreement of the 
profane history with the sacred history." When 
one perceives in the seventeenth and eighteenth 
centuries that the common chronology, placing the 
origin of the world in the year 4004 B. C., was too 
circumscribed for the developing knowledge of the 
times, he beholds it still more in our own days — 
when the natural sciences have cleared away many 
of the doubts, errors, and mysteries of the past, and 
show the sublime beauty, grandeur, and perfection 
of God's works. Tliey carry us beyond the time 
when there was no sun, no moon, no stars to shed 
light on a new-made world. Verily, there is some 
trutli in the words : 
" More things arc wrought . . . 
Than this world dreams of." 
Science is the great light which enables us to see 
countless beauties in the visible creation where 
before we could only see with the dim organs of the 
senses. Still, science has its legitimate sphere, and 
must not enter the domain of theology and dogma- 
tize. Its proofs must support its conclusions; and 
not only must its proofs support its conclusions, but 
in its terminology it must maintain exactness of 
definition. One does not ask himself today, like 
Pezron and Tournemine, whether we should not 
substitute the chronology of the Septuagint to the 
more short one of the Hebrew and Vulgate. The I 
longest is too short to satisfy the just demands of 
the geologist; and yet there is, at times, a reckless- 
ness about some geologists who demand improbable 
periods of time. A thousand years is to the geolo- 
gist the same as a day is to the historian or journal- 
ist. And while we are willing to concede thousands 
— yea, millions — of years to them, we expect at the 
same time that geology will be in harmony with 
other natural sciences. 
There is one point in the issue between natural 
science and revelation, which, if viewed in proper 
light, will harmonize both, for there cannot be any 
conflict between them, if one understands the other. 
First, we are to distinguish between the antiquity 
of the world and the age of man, because these are 
two different things altogether in their relation to 
Scripture — the earth having been created a long 
time before the first man. Thus we see that Scrip- 
ture does not teach us anything about the epoch 
when the universe was formed, nor does it appear 
to contain a theory of creation. It asserts creation, 
providence, and fatherhood, but how matter was 
created, and how after its creation the divine agency 
was corrolated to it in producing new forms of life 
and beauty, Genesis does not declare. 
The views expressed by those advanced minds in 
past centuries have been confirmed by the develop- 
ment of geology. It is no more a question of doubt 
about our planet being very ancient. The more 
accredited systems on the formation of our globe 
require almost countless periods of time, but for the 
present will content ourselves to the scrutiny of 
geology and its most certain conclusions. Half a 
century ago, when the science of geology was in its 
infancy, a cry of alarm was heard throughout 
Europe, that the new science was an attack on 
Genesis. The learned were soon able to reconcile 
these misgivings, and now it is largely a Christian 
science. 
Our ideas as to the method in which the strata 
took place in the early formation of the earth may 
differ, but as to the estimate of time we must all 
agree to long periods. Geologists are unanimous, 
with a few unimportant exceptions, in saying that a 
very long time must have elapsed before all the 
strata, many of which are in places several thousand 
feet thick, attained their present form. G. Bischof 
calculates the duration of time for the formation of 
the earth at three hundred and fifty-three millions 
of years, and Pfaff thinks it likely that the solidify- 
ing of the earth's crust took no less than twenty 
millions of years, and not more than four hundred 
millions of years ago. The time which elapsed 
between the beginning of the Carboniferous Age — 
which constitutes only one of the divisions of the 
Paleozoic period — and the recent period, is supposed 
by Arago to have been three hundred and thirteen 
thousand six hundred years. G. Bischof estimates 
it at one million three hundred thousand in one 
passage, and in another says it may have been nine 
million years. 
Owing to the want of space, we can adduce only 
one illustration in this article to show what a " long 
period " means. In order to form the Saarbruck 
coal beds, which are four hundred feet thick, a 
mountain of wood two thousand four hundred feet 
high would have been needed, supposing them to 
have been formed of vegetable matter. Now we 
know that our forests hardly produce a layer of 
wood two inches thick in a hundred years ; there- 
fore, a mass of wood such as we mentioned would 
take at least one million five hundred thousand 
years to grow and a corresponding length of time to 
form into coal. This calculation is based on present 
accretions of vegetable and earth matter in forma- 
tions of the coal measure. It is very probable that 
the primeval flora grew much quicker than it doe» 
