Year: 1876

The pendulum test is OF course rudcr one. but
necessary to the oscillation caused by the
terrestrial disturbance in drectien at right angles TO
that indicated by The spirit level.


The results obtained by these tests have been most
satisfactory determining the radiation of the shock
and the peculiar modification OF its intensity produced
by the medium through which II was transmitted Be.
ginning at the points nearest to the Of explosion
the following effects were observed by tho HERALD
corps-


Wards ISLAND


The test was made as point situated on the pro.
lonsatono tho axis of Haletts Point reef northward
and distant from the explosion and beyond the Insane
and lnebriae asylums. The spirit bubble vibrated
half inch, whilc the in tho tumber was agi.
tated strongly by waves passing from the rim
toward the ccntre throwing up q globule
The pendulum showed lateral vibra-
tion. charlottesville shock was transmitted
to this point in depressed curve, tho force OF the
blow bcino obliquely upward in the direction of the
axis Of tho rect The shock distinctly felt before
the noise of tho explosion heard showing that its
velocity exceeded 100 feet per second and probably
attained three times that speed There no percept
lille concussion of the air because the point OF
was below tho centre of atmospheric disturb.
ance which fully 100 ce above the surface of tho
water and spread on plain at that level


BLAcKwELL's ISLAND.


The point OF observation the northern end OF
the Island, near the lighthouse and nearly on limo
with the axis OF the reef Tho bubble OF the spirit
level broke in two with the shock The In the
tumber rosc TO point In tho centre, and
In the return movement to tho rise over
flowed equally all around the glass The pendulum
showed lateral movement Deductions: Tho
shock at this point almost vertical on account Of
the deep of the river bed between the explosion
and the end OF Blackwcrs Island, which formed an
invert by which the transmission Of the shock was
controlled


FOOT OF NISErIErH STREET, EAST RIVER.


Neither tho spirit level the pendulum recorded
any perceptible vibration at this point The water In
the iumbler slightly agtated but no rings were
formed the surface. Tho disturbance beng limited
TO trcmuous movement Of the water due to a slight
vibration. Dcductions:--The observations show
that the shock was intercepted first by
the depth Of the river channel and, secondly, by tho
deadcning influence Of the lamination o. tho rock
formation, which prevented the transmission of tho
vibration. 1t is certain, however, that the shock
passed undor tho point through the denser substrata
without affecting to any extent the surface rock.


BELvEDxnE TOWER, CENTRAL PARK


Hero the vibration did Affect either the bubble OF
the spirit level agitate the water In the tumbcr but
moved pendulum pointer about two seconds toward





second after hearing tho report 1t success
of four or five slight vibrations and entirely
atmospheric. Deductions: Tho transmission of the
vibration toward this point was similar to those re-
fcrrcd to in tho of Nincticth street. which is
almost in tho samc line with Hallctt's Point reef Tho
place being elevated, 1t affected by tho atmospheric
concussion, which at this distance moved slowly in a
OF vibration and at lower velocity than sound.
The movement Of the pendulum was so little ndi-
cate only extremely slight lateral OF
vibration from the reef, which to have almost
entirely exhausted It's force the limo OF Lexington
avenue.


sxrY-youRrn STREET, NEAR THIRD AVENUE.


At this point tho jar quite perccptblc causing
light articles such knives on tables In tho
Easements. and 10 shake tho doors with prolonged
vibration Deductions: Tho shock hero vertical and
evidently passed under tho Intervening strata that cx
tend between tho point OF observation and tho reef
The atmospheric effect also very pcrceptibIe be.
tho plane Of greatest atmospheric vibration as before
Indicated


sIxrrETn STREET, NEAR LEXINGTON AVENUE


Tho observation at this point was limited to tho
tumbler test The glass was filled to the brm and pro-
tcctcd from the action Of tho wind Before the blast
the remained perfectly otonlcss. but when the
explosion occurred It covered by tremulous mo-
tion, commencing at the edge and moving toward tho
centre Ike that surface vibratory produced
when wet finger Is rubbed around the rim OF glass;
Deductions: Al this point the vibration was also
nearly II not wholly vertical, and had almost ex-
hausted its force by passing oblqucy through the var
GUS formations in It's course.


RESERVOIR SQUARE, SIXTH AVENUE.


At this distance tho vibration was almost nil, no
perceptibe effect being produced the testing ap-~
paratua A magnetic disturbance. however, was OBJ.
served which lends great interest to tho observation
About two seconds after the explosion was heard tho