The sun. [volume] (New York [N.Y.]) 1833-1916, 1906-09-09
ENDS OF TUNNELS WILL FIT.
Pm. n. ENGINEERS REVIEW THEIR
WORK AND FIND 1T GOOD.

A1HN 1917
Tubes Are Less Than n Inch Out Of
IAne-Just = Little Problem I'm TrIgO-
nOmetry-NO COrrcc tl0ns Necessary.
When the human moles who for a year
have been driving the twin tunnels for the
Pennsylvania Railroad under the North
River laid down their shovels at midnight
a week ago Last night they had been called
of 10 that Chief Engineer Jacobs and his
corps Of assistant engineers might spend
the week checking up the grade and
alignments OF the big tubes. The review
Of the work that has been lone was COM
pleted yesterday.
When the actual digging was stopped
last week the shields that had been Rp-
preaching each other, two from the Jersey
shore and two from the Manhattan side.
were 12s feet apart. zach OF these pairs
of shields is expected to meet on September
IS. Before the work had gone too far for
correction, however, the review and check
ing were decided upon to make sure thas
while the laborers had been delving through
the black mud they were not headed in the
direction OF Tombstone, Arin., instead OF
Jersey City and Manhattan.
As had been expected said Mr.. Jacobs
yesterday, we found that We had not been
going it sc blind. as would appear to the
lay observer. Dur careful measurements
Of the past week nave shown US ~conclusively
that the tubes are less than n inch out
| OF line, or, TO go into details, they are only
o~ne-eiGhth Of an inch of in alignment and
t~hree-quarters OF an inch OF grade. Con-
seduently when the eastbound a west
bound advance shields Of either tubs meet
the middle OF this month there will be 40
nice q fitting Of the cast iron lining that
the difference between them will be hardly
noticeable"
This digging away down there in the
mud, rock and darkness does have the
appearance to a layman OF going 1t blind
I Nevertheless the results OF this weeks
checking up show that the work a gone
ahead with the same certainty as with work
done on the surface, where each part could
be measured constantly in relation to q
corresponding section Of the approaching
work.
Mr.. Jacobs smiled yesterday when the
awestruck reporter suggested that this
checking OF tho alignment OF the tubes
must be a very difficult matter with the
ends Of the tunnels still 30 far apart.
Il suppose Il does seem mysterious to
one who il not an engineer he said, -but
it really all comes down to a e simple
problem in ~trigonometry. After our work
OF last week the engineer knows just how
one shield will meet its approaching mate
as certainly "a il he had seen them meet.
In driving the two tubes under the river
Nc did not keep tho shields OF the north
and south tunnels abreast OF each other.
In the north tunnel from Manhattan We
sent the shield some distance ahead OF its
southern mate and in the south tunnel
from the jersey shore the south shield
was pushed ahead OF its northern mate.
The result was that when the laborers
stopped work a week ago the shield OF the
northern tube that Il headed west was a
good deal further out from the Manhattan
shore than the shield Of the south tunnel
that 10 being dug from Jersey City to New
York.
This difference OF progress between
each pair was carried out simply to give
us something to work on in the last week
while checking or verifying, By driving
six inch hollow pipes OF at right angles
to the alignment OF the tubes through
the fourteen feet that separates the tunnels
making these hollow pipes run from the
northern tunnel to the southern, l a
we Immediately had some angles formed
to begin with.
"A line surveyed through the centre
Of the big tubes formed a right angle with
a line sighted through the small pipe run
ming from tunnel to tunnel. Then when
the four lines running through the two
tubes and the two pipes were Joined We
had four right angles OF a square. After
this had been lone the rest was q mere
matter OF mathematics.
ALSO with the aid Of the six inch pipes
we found the course of the grSds align
ment. Levels were transferred Tfom tube
to tube by means Of the pipe and in ibis
way the grade was found Is Be practically
exAct We are very we'll satisfied with
our review Of the past week, because w
can now send the tubes forward TO COM
pletion without any doubt that they viii
meet as designedF/
The checking OF the work was lone At
this time beoanse the two ends OF each
tunnel are still far enough agart to permit
Of correction II any serious error Of grade
or alignment had been found. With a
deviation OF less than an inch; however,
FROM the theoretical course practically
no correction will be necessary.