Fuly 1, 1886 | 
NAT 
ORE 205 
small, are distinct and c»mplete, and the feathers Jarge and 
definitely arranged. The emu, cassowary, and apteryx show 
various degrees of degeneration, which apparently culminated in 
the dinornis, no trace of a wing-bone of which bird has ever 
been found. The question which naturally presents itself with 
regard to these birds is, whether they represent a stage through 
which all have passed before acquiring perfect wings, or whether 
they are descendants of birds which had once such wings, but 
which have become degraded by want of use. In the absence 
of palzontological evidence it is difficult to decide this point. 
The complete structure of the bony frimework of the ostrich’s 
wing, with its two distinct claws, rather points to its direct 
descent from the reptilian hand, without ever having passed 
through the stage of a flying organ. The function of locomotion 
being entirely performed by powerfully developed hind-legs, and 
the beak mounted on the long flexible neck being sufficient for 
the offices commonly performed by hands, the fore-limbs appear 
to have degenerated or disappeared, just as the hind-limbs of 
the whales disappeared when their locomotory functions were 
transferred to the tail. This view is strengthened by the great 
light that has been thrown on the origin of the wings of the 
flying birds by the fortunate discovery of the Archeopteryx of 
the Solenhofen beds of Jurassic age, as in this most remarkable 
animal, half lizard and half bird, the process of modification 
from hand to perfect flying bird is clearly demunstrated. The 
three digits which in the existing forms are more or le s pre sed 
together and imperfect, still retain their freedom and complete 
number of phalanges, and are each armed with terminal claws, 
while the flight feathers and remiges of the cubital, metacarpal, 
and digital series are fully developed and evidently functional. 
The earlier stages in which the outer digits were sul present, 
and the feathers imperfectly formed or merely altered scales, are 
not yet in evidence. 
Some conception of the process by which a wins may have 
been formed may also be derived from the study of the growth 
of feathers on the feet of some domestic varieties of pigeons 
and poultry, illustrations of which were shown at the lecture. 
THE SUN AND STARS}! 
VII. 
WE have now to endeavour to apply to the more distant stars 
some of the facts which I have brought before you touching 
the nearest one—our sun. What we have to do in the short 
time at our disposal is to choose those facts which will give us 
the greatest amount of knowledge concerning the greatest number 
of those stars. 
When the star that is nearest to us has set, the number of stars 
which a pair of eyes can see on a dark night, whether they 
happen to be north of the equator or south of it—for the number 
of stars is pretty equally distributed north and south—is some- 
thing under 3000. But when we leave behind us the power of the 
unaided eye, and consider what re ults can be obtained by the 
optical means now at man’s disposal, we have to increase these | 
6000 to something like forty or fifty millions, so that, if we can 
by any chance obtain facts touching one star that are applicable 
to others, we do a great deal. We ace, in fact, dealing with 
50,000,000 bodies instead of one. 
The first thing regarding these distant bodies to which I have 
to draw attention is that they have been divided for purposes | 
of convenience—astronomical and other—into magnitudes such | 
that the first magnitude means the brightest star we can see ; 
and so we go on till now we go down to the sixteenth magnitude. 
The order of diminution of brightness is not quite exact from 
the first magnitude to the faintest visible to the naked eye, but 
it may be taken on the average to be about two-fifths. If we 
take this ratio as the normal one down to the sixteenth magnitude 
we get the following values nearly :— 
2% stars 2nd mag. 
I star Ist mag. 
6 3rd = rh 
16 4th = a9 
40 5th = ” 
100 6th = «5 
10,000 rith = AD 
1,090,000 16th = <4 
* A Course of Lectures to Working Men delivered by J. Norman Lockyer, 
F.R.S., at the Museum of Practical Geology. Revised from shorthand ! 
notes. Continued from p. 45. 
We not only get the stars thus visible, but, as they can 
be photographed ina certain period of time, this period measures 
their photographic brightness. We find, for instance, that a 
first magnitude star can be photographed in the three-thousandth 
part of a second ; that a star of the seventh magnitude can be 
photographed in about one second ; and when we come to the 
twelfth magnitude we must turn seconds into minutes, and we 
shall require two of them to get an impression on the plate ; till, 
working on gradually to the sixteenth magnitude, we find that 
the photographic plate, which requires only the three-thousandth: 
part of a second for a star of the first magnitude, requires one 
hour and twenty-three minutes (or eighty-three minutes) to receive: 
the impression, we find the ratio of two-and-e-half times to be 
practically indicated by the times of exposure. 
The relative photographic light of stars of all magnitudes when 
the most rapid dry plates are used is shown in the following: 
table :— 
‘Time of exposure 
Magnitude m. Ss. 
Ist 0005, 
2nd o'013, 
3rd 0°03 
4th 008. 
5th 0.2 
6th o's. 
7th 13 
8th 30 
oth 80 
roth 20°0 
rith 500 
12th 20 
13th 50 
14th 13/0 
15th 33°0 
16th 83°0 
We must not for one moment imagine that, because for many 
reasons it has been necessary to divide stars into magnitudes, 
| all the stars are of exactly the same size at different distances, 
or of different sizes at the same distance. We know very little 
at present relatively. But this we do know, every new fact has 
shown us that some of the apparently fainter stars may be very 
large, and some of apparently the brightest stars may be small. 
You can understand that the light which we get from the stars 
will depend upon these two things. Take the case of the sun 
for instance. We know that the sun is a small star, and yet it 
gives us a great deal of light because it is near to us. We know 
that some of the other stars are very distant, and they give us a 
small amount of light, not because they are small, but because 
they are so far away. 
We are living now in a very interesting time, because people 
are beginning to work here and there, not in too many places, 
to get the stars to write their own autobiography, so to speak. 
In fact, a very important attempt is being made at the present 
moment to replace observations of the positions of the stars by 
actual photographs. Observations, you know, being human, are 
always liable to error. ‘Ihis plate, which I am about to show 
you, is a photograph that I have received from the Brothers 
Henry of Paris only this morning, showing what photography 
can do in registering the exact positions and brightnesses of an 
almost innumerable army of stars by simply exposing a plate in 
a telescope. 
If it is wished to obtain photographs of stars of the sixteenth 
magnitude, the plate will have to be exposed eighty-three 
minutes. If we are content to get stars of the seventh magni- 
tude, then two minutes will be enough. 
All the stars that you see here are visible in a very restricted 
portion of the sky in the constellation Cygnus, not very far from 
the Milky Way. You can understand what a happy thing it will 
be for the astronomer of the future if, when he wants to know 
the state of the heavens in this nineteenth century, in- 
stead of having to consult musty books of observations which 
may probably be wrong, he can refer to a book of which the 
leaves are made of glass, and on which is recorded the auto- 
biography of every square degree of the heavens as you see on: 
this diagram before you. 
In our attempt to apply to these other bodies the knowledze 
which we have acquired touching the sun, of course we have to 
consider chiefly the light sent to us by them. You will see 
in a moment that if the sun were very much farther away from 
‘ys than it really is—imagine it for a moment so far away that 
