, 1874-03-22

altered our conceptions OF Lie con6tructl0n and
classification Of living forms. which shows that
the sknll is but modified vertebra aud the 1orar
| modified leaf. is gradually being applied to
! other departments of science than the nera
structure OF living beings; and there dawna
upon US tho idea that, in tho
growth and motion, the uses and pur-
poses, OF the organs OF animals, there il
| the same link Of interconnection, which onI9
| awaits patient investigation to stand revealed.
! The guiding principles which hre involved in
! this work Of Prof. Pettigrew, which ara con.
| stantly recurring in it's pages, and which ha7s
been the subject Of numerous experiments, may
! thus be succinctly stated in his own words:
Firsl-That quadrupeds walk, fishes swim,
and insects. bats, md birds dy, BY fSu1e-of-a
| movements,
Second-That the hipper Of the sea-bear. the
swimming wing OF the penguin, aud the wing Of
tho insect, bat, and bird, screws structurQny,
aud resemble tho b1ade Of An ordinary SCREW
propeller.
Third-Tbat thase organs are screws Junction.
ally from their twisting and untwisting, and
from their rotating in the direction Of thoir
length when they are made to oscillate.
BY hgure-of-8 movement is meant the cures
INTO which the extremities Of a body are thrown
when in motion. Tho line which the feet Of e
| four footed quadruped, the tail aud body Of
fish, and the wings OF bird describe, On tho
land, in.the water and in the sir, is that which
Is shown in the outline OF the figure eight.
Thus: O. In man, among bipeds, tho
leg advances in curve, pendulum
fashion, is planted upon the ground, and upon
this foundation the body rolls forward, tho
head OF the femur forming the oentre Of
circle the raiius Of which is described by the ad-
vanciag foot Walking is consequently to b
regarded as the result OF a tFistiDg diagonal
movement in the trunk and tbs extre.ni::es-
Without this rolling motion, advance could ONLY
be made by series OF leaps. In the swimming
Of the fish, the body is thrown into the dorb!a
OF fgure-of-8 curves. as in the walking Of tie
biped. The wing of the bird does not differ ma
terially from the extremity OF the biped or tho
tail Of the fish. Ii all, tho waved tracks are DE-
scribed. All wings are constructed upon cun-
mon type. TheE are. in every instance, case-
fully eraduated, sapering from the root towards
the tip, OF = ttiaosular form, and twisted upon
themselves in the direction of their length to
form helix, or screw. In the dipper OF the
gea-bear and the swimming wing Of the little pcn-
guin, no less than in birds aud insects, tlo
screw~shape OF the organ is too obvious to need
comment. The bouy skeleton OF the veretbrstes
is secondary IN importance to the muscular ays-
tenn, and the bones are twisted upon them
selyes in the form OF SCREWS, thus
being adapted to the. wants Of the muscles.
Bones have no POKER either Ct originating CT
pezpetuasing motion, which begins and ter1ni-
Mates in the muscles.
The angle at which the bones Of the limbs are
inclined to each other, and to the trunk. reyu-
lates the speed Of animals. In the deer, the
heetest Of quadrppeds, the bones Of ths extreme
ties are inclined very obique1y, and, By thus in
creasing the leverage Of the muscles, great speed
is attained. They ara less obliquely inclined in
the horse, still lees in the elephant; while in
man, from the skeleton being nearly
erect, together with the fact that FAIL
Of the power which should movs the
limbs is dedicated to supporting t:s
trunk, his speed is very much diminished. The
limb Of the ostrich is the very embodiment Of
speed, enabling the bird to ontst1ip the heetest
horses without difficulty. In running, IL is
greatly aided by its wings, which, though totally
useless for fight, sa1ve to maintain its equili.
b1iun, and thus afford powerful aid to the bird
Upon the land, solid aud unyielding, tho ,e1-
tremities Of qradrupeds are. as rule terni-
mated by small feet. In those beings inhabiting
water. they ara furnished with more extensive
surfaces, which, by de1trous fitting or twisting,
acting upon the yielding medium with great
force, produce locomotion- In the fish, loco
motion depends upon the tail and lower
portion Of the body In the porpolse, the man~
atee, and the seal, there is progressive differ
eutiation toward the use Of the anterior e1t1smi-
ties for 1ocomotion, which. in the sea~bear. arc
sufficient to enable tire animal to progress bF
their aid alone. As connecting link betTeen
animals which progress in the water Gad those
which inhabit the air. ne have the diving bids
On one hand and the flying fab On the other-
In the little penguin, the wing forms perfect
screw, and % such is used il swimming and
diving. In the dying-Ash. it's greatl5-e1-
panded pectoral fms act after the manner
OF kite, aud its fight is to be regarded
rather as IN example OF akimmng OF sailing
flight than Of ordinary flight which is character
lied by a tapping and gliding action OF tho
wings.
The difference between sub-aquat1c ano
aerial fight is. that, in the one, the effective
stroke Of the wing is delivered dotrnrards ind
backwards which, in the other, it ia delivered
dolen,cards snd fortcards. Weight il sn III
portant auxiliary in aerial flight, AZ lghtness
in sub-aapatic. With the rtroke dovnwards apa
forwards the bird in the air would be caz1leo
from the earth without the power - :c.+afn. IN
snb-aquatic flight, or diving, ightness uoeo
insnres return to the surface.
The modes OF 1ocomotion On the earth and II
the water arc COARSE and unwie1dy compHe1
with the fight Of the inhabitants Of the ar. Ii
a medium Of such extreme teuuity - the 81
mosphere, the most delicate adaptations BE-
comes necessary. It would require much sIace
to follow Prof. Pettigrew in his EXPLANATIONS
OF, and experiments upon, the subject OF hen'
Suffice it to say, that the same principle o1 .o'
screw is applied throughout his exceedi0gl7@'o-
.teresting presentation OF progression IN oe
through the sir, and hin pages are r.
plete With illustrations and dlAEfa'n7
fully elucidating his theories. oSe
fact may be noted in Pa7.
ing: He regards the prope1lers at psese:'
employed in navigation as faulty in pf1nc'ps
and applicstion, from the fact that, to ope1f1'
efficiently upon the yielding fluid (eisher WILL
or air), the propeller itself must yield.
In q short final chapter on Aeronautics, ff".
Pettigrew considers the subject Of arade"
flight. Two schools upon this question e1's&:
1 11atr.+x,,;r%a %}oaa rvfr ~1vaeHfe thA Ell