New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1871-01-28
TIE TIDES IN NETWORK HARBOR.
A LECTURE BY PROF. J. z. HILGARD.

A LECTURE BY PROF. J. z. HILGARD.
The fifth of series of scientific lectures be-
the American Institute was delivered by Prof j. H.
Higard OF the u g. Coast Survey, ut the Academy OF
Music last evening" Tides and Tidal Currents and
their Effects upon HarbOrs" The lecture was illustrated
by 20 diagrams shown upon SCREEN on very enlarged
SCALE by means OF the magclantern. New-Ydk Harbor
said the lecturer. has two entrances-one from Long
Island Sound, the other by way OF Sandy Hook. The
former natural depression, arm Of tho sea- which
Is not changed the forces now In operation The tidal
currents which flow through 1t do not change the chan
mel but are obliged to follow 1t in its tortuous course
The Sandy Hook entrance the contrary is character
lied by Gordon Of sands, extending from Sandy Hook
10 Coney Island intersected by channels, which are
maintained against the action Of the that tend to fill
them up the Of the ebb tide from the tidal basin
Of New York Harbor.
The depth Of "a feet at low water, which the harbor
now Possesses in direct channel may be considered as
depending upon the following elements: ~ The large
basin between Sandy Hook and Staten Island including
Raritan Bay which furnishes than Onehalf OF the
sa 81 wi and NEWARK Fay IS North
bobbs Ferry maintaining the head OF the ebb
portion OF the Sound tide which flows in through Hell
Gate. Tho two tides, from the Sound ana rom sandy
since they differ from each other in times and nights
they cause differences Of elevation between the Sound
and Harbor which produce tho violent currents which
The conditions OF the tidal circulation through Hell
IA
water would times stand nearly five feet higher on
one side than the other and again five feet lower on the
same side The westerly current usually called the epb
stream taking place when the Sound tide Is hlghest,
starts level 81 feet higher than the eastery cur
rent and thus much larger amount OF water n0ws out
OH the Sandy channels than through Throggs
Seck IL IA apparent, then that this portion OF the eDD
stream reinforcing rs IL does the ebb stream
of the harbOr proper, at the most unlaVorape
times performs q most Important part III nam.
t,iung the channels through the Sandy Hook bar. ~
may be esma ted that the closing or HeilGae wouia
cause loss of cerIuny not less than feet In the depth
81 IN asna
we now have il IL important that the area OF the tdaI
basin should not he encrOached upon In proportion us
that ia diminished the depth OF the channels VIII de
crease The flats Just bare NJ low water bt covered AZ
hjch tide perform important part as any other por-
ton for IL is that t Is only the tidal pressure
tba2 does any work securing the channels The wafer
ON the flats especially useful by retarng 0utnOw mus
allowing greater difference Of level 30 DO reached De-
tween the basin and the ocean -----. ...
When we yield to the demands OF commerce. any
notion OF the tidal territory must do 80 with full
rogniyance OF the sacrifice about to make In the
depth OF yntcr in the channel From what mas oeen
s,id with regard to the meetings OF the tides IN Hell
GATE II will be that tho violent currents expt
rien.ed I'M that locality duo to causes beyond cur
contro The dangers 10 navigation arising from THESE
currents however by their setting vessels upon the
rocks md reefs may, In great measure. DO done away
with by the removal Of the DISTINCTIONS In wncn %or
considerable progress has been made inc removu ~,
reefs at Uallett' Point which Is now looked lor win
tunbtless in great degree, do away with the eG .
aud currents produced by the sharp turn which the
channel now takes at that point. IL Is not mpropaoc
that the Sound entrance may yot become mo VI
NnpL Hnrh