Year: 1870

passage III the masonry by powerful
steam pump. The caisson with its super.
structure Of masonry must be sunk to the
rock bed of the river, because the depos.
it Of sand above it-which at one pier is
10 feet deep--in times of food and fresh
ct, is secured away to great depth, il
not to the rock itself. When the caisson
reaches the river bed the sand within it
must be removed This is done by a
current of water that is forced down, by
tube, through the masonry, into the
caisson and then up again to the surface
and as it takes its upward course the sand
is shovelcd into it through n contrivancc
for the purpose, and carried to the sur
face in the form Of muddy water by the
ascending current and poured out into
the river. Here it causes bank of sand
to accumulate which sometimes rises to
the surface Of the water.


Workmen are needed in this caisson of
condensed air, below the bed of the river.
to shovel the sand and do other necessary
work. These pass down by means of q
circular stairway in another vertical pas
sage-therc being five in al-through
the center of the pier, and are admitted
into the caisson through an air-lock or
chamber, with an air-tight door on the
upper and lower sides Into this cham.
Der, after the men have passed the upper
door, the condensed air is gradually ad-
mittcd till it is dense in the lock as in
the caisson below. They experience here
very peculiar sensations, among which
are, a burdensomc pressure upon the
whole system and especially upon the
drum Of the ear and great increase of
heat in the system, because condensed air
has smaller capacity for heat than in its
ordinary state. In passing out, of course,
the order of proceeding and of sensation
is reversed. The workmen in the caisson
are exposed to considerable danger from
the unusual atmospheric pressure which
sometimes amounts to two or three atmos-
phcres. Several have died from the in.
juries here received. When the caisson
has reached the bed rock, the bed "dps'
towards the Illinois shore, is leveled off
with concrete; and the sold pier rests
upon a foundation of limestone rock.
Two piers have been sunk in this manner
and are now above the surface of the
water; the last will be similarly sunk this
fall.


The manner of testing the steel which
will form the arches of the supcrstructure
is also very interesting This is done BY
means of a massive machine which acts
by hydrostatic power. BY its use the
power Of the steel to resist both compress.
sion and tension is accurately determined.
1t is well known principle of hydrosta-
tics that given pressure upon one square
inch Of liquid surface causes equal pres
sure upon every inch of that surface
This instrument is so constructed that the
surface where the power is cxcrtcd is to
the surface Of the piston where the power
is applied as to 100; hence the exer.
ton Of one pound Of power produces a
compression or tensl force of 100 pounds.
Any change in the length of the steel to
be tested, even to the 20.000th of an inch
it is said can be detected This change
is indicated by mirror, which rcvolves
as the piston moves, and which reflects
light from II graduated are, - feet dis
tant, to telescope situated in the are.
Through this the observer looks and re-
cords the continued changes Of the steel
by the vivied pressure to which it is sub
jected. Every piece is tested until its
limit Of elasticity is reached, that is,until
1t has become so compressed that it will
not spring back when the pressure is re-
moved. 1t may be subjected to force of
| 100 tons.


BALLou's MAGAZINE FOR DECrMBER.-
The first in the field for December is
Ballou's Magazine, and an examination
Of it shows that it is model number in
every respect. The engravings are ex.
celcni, the descriptions ingenious and
eloquent, while the stories are remarkable
for their interest and great originality
Mrs. Edison finishes her continued story,
and lloratio Alger, Jr., concludes his
"Snk or Swim" in satisfactory manner,
as the juveniles will learn when they read
it. Macy has finished sea story in his
own particular vein. Stephens gives us
IAN evening with Il Catamount" Dar-
ling tells us "Why our Wedding was
Postponed in his most comicai manner,
and then there is Christmas story, full
of humanity and goodness, and three Or
four love stories which will bear perusal
half dozon times, and Lost and Found
is Il regular California tale, by new as.
pirant for fame in the columns of Ballou.
In addition to this there are many arti-
clcs worth reading, in the shape Of sketch
cs, poetry. etc, etc, and all for the sum
OF 10 cents per copy, or Sl.5O per year.
The December number closes Vol. b.
The New Year will commence with many
rare novelties, so don't delay in making
up your clubs or purchasing at the peri
odical depots. Thomcs 4 Talbot, 63
Congress street. Boston, are the the pub
fishers Sold at the REGISTER News
Room.