New-York daily tribune. [volume] (New-York [N.Y.]) 1842-1866, 1851-05-12

py " % ha read hv M. WhtsHey' ou' owing 70
.S.ence brief explanation only vas given
AZ Mr. Foster detail vas s 90. .. .ue uoo O
ys.i .,ructure Of KeSeenaw Point win gen
iogica y. - the entire Iron and Copper Region.
n, ~. mail closes, and the remainder Of to-
DAVIS proceedings must De pO''p0neo' An
,oo,v .crscIsNArI, Tuesday, May SPIN
onO'.,s Under Of this mornings proceedings
- four pspers-from Prot. HENRY, OF
co",,'' ,.L.o,;sp Institution Prof BAcHE, Of the
INC oN o.-vsv. Mr.. PORTALS, of Washing
U0" - WIZ. c. REDFIELD Esq, Of New.York.
'0 tn, communication Of Prof Henry was on the
.,Iini, Of Perceptbility Of Direct aud Reelected
co.nd and gave an interesting account of bis re-
osnt experiments on Acoustics. The following is
An abstract;
I,u- M PERCEPTIBiLITY OF A DIRECT AND
LiAii NF REFLECTED SOUND.
pof UEsRY stated that at the meeting Of the
A.socis,ion At Cambridge, he had made a commu.
nic.,io. relative TO the application Of the prlnci-
Les of acoustics to the construction OF rooms in.
landed for public speaking. Ia that comm unica-
ZION be had stated ss an important proposition
tb,t when two portions Of the same sonOrOus
rave reaches the ear Of al auditor, one directly
from the origin Of the sound. and the other indi-
rectly after one more reflections, il the two do
not differ in the paths they travel by difference
greater than given quantity, the two sounds
will enforce each other and one louder sound will
be perceived-if however, the interval is greater
than a certain limit, the two sounds will appear
distinct or an echo will be perceived.
As an illustration suppose speaker 20 stand
before wall at the distance OF say 10 feet; In
this case the audience IN front would hear bat one
sound. The direct and the reflected impulse
ynset the ear within the limit which have called
the limit OF perceptbility. This limit, knowledge
nj which ia of considerable practical importance,
NAV rather be expressed IN time or IN space.
The simplest method Of obtaining us amount is
that OF clapping the hands while staholas before
. nernendicular wall il the distance OF the oo'
49, he snpicient an echo will be heard. II in
mi. case the observer gradually approach the
wall and continue 10 make the sound al de1nue
point the echo will cease 10 be perceived anu tue
two sounds will appear a. one. IL tue distance
from the wall be now measured, Twice tue u's'snco
faund IN give the lint OF perceptblIlty In space.
m the same quantity be divided into the space
tbroueb which the wave OF sound ls known to
travel in second, we shall have the limit OF per-
ceptlblllty IN time: 49,.
The foregoing plan is the most simple, but not
the most accurate method OF arriving at the guam
titv sought The better plan is TO employ another
psrson 20 produce the sound while the observer
u stationary at the distance-st least hundred
and ffty feet from the wall. The person who
produces the sound being placed between the oo
server and the wall, at such distance from the
latter as TO give distinct echo; ne ls then di'
rected gradually to approach the wall until the
echo and the direct sound become one. The DIS
lance measured as before mentioned, will give
the limit required
From series Of experiments on TINS plan
Prof II found the limit OF percepnolllty 20 vary
from about 90 TO 50 feet, o., IN other words, the
distance from the wall at which the echo ceased
was from 30 TO 40 feet This will give from the
l.QOto the lis part of q second IN time for the
20 distfO iah ha SOUNDS
which follow each other at Gu interval OF Lilo oil
second
The experiments when made under the same
circumstances gave the same result almost with.
in single foot, but when different source oil
sound was employed and different observers
there was observed the difference of results CIV
ing the limits between l.2O and l.15 OF second.
The limit was less, with sound produced by an
instrument which gave sudden crack without
perceivabe prolongatOn, such as is produced by
an ordinary Waterman rattle when made TO emit
single crack. This difference may be explained
by taking into consideration the actual length OF
the sOnOrous way. II a sound occupies OF
second, which is about the time required for the
utterance OF a short single syllable, the length OF
the sOnOrous wave will be about 300 feet, and
hence when the distance travelled by the two
sounds is not more than go feet 70 and from the
wall, the two waves must overlap through con-
siderable portion Of their whole length, and will
be only separated at the two extremities The
portion Of overlapping may therefore determine
the limit of perceptbility, and this again is COM
bined with the TACT of the continuance OF sonor-
Gus impression on the nerve OF the ear.
The next paper was by Prof. BAcHE, Superin-
tendent of the Coast Survey, upon "Curren'
Chart Of New-York Bay 1t was as follows;
CURRENT CHARr OF NETWORK BAY, FROM
OBSERVATIONS IN FHE COAST SURVEY.
ny A. D. BAcBE, sUiERINTENoENr.
A. AL ~ m iafiO In Va n
ven, said Prof Baohe, presented Current
Chart OF Boston Harbor from observations by Lieut.
Cong Maflitt L .S.N assistant in the Coast Sur
vey, upon a plan devised by me for representing
the direction and velocity OF the currents at the
surface. The Chart now submitted to the Asso-
ciston exhibits the results OF observations made
In New York Bay by Lieut. Cong. Charles ii.
Davis, U.SN, assistant in the Coast Survey, and
Is upon the same plan with the former Chart.
The Chart of Boston Hsrbor illustrated the Of
feet Of obstacles al aud below the surface, M
Islands, rocks, &c, in DETECTING the current aud
modifying its rate. The second shows the lnhd-
ence OF great Bay, aud Of obstacles below the
surface, consisting of shoals OF various masnl-
tudes and different degrees Of elevation above
the general snrfsce of the bottom. The Chart
shows the direction and velocity OF the water at
foods.
The parallel lines indicate the directions OF the
currents and the distances between them and the
inverse proportion OF the velocity. AS tue SuAN
Is nom observations NJ limited number oil STA
tons, the extent of particular directions and We
locties is not rgidy defined. the eye SEXES
rapidly the CONGRATULATIONS Of the facts aud with
certainty which tabular view Of the results
would enable the mind to grasp.
The scale of the Chart now shown Is such that
aveOciiy Of half a mile per hour is represented
by distance Of halt al inch between the paral'
lels, and greater Veloeties by prOportlonately
less distances.
The water from the Ocean sets into New-York
Bay in direction nearly perpendicular TO line
from Rockaway entrance 10 Sandy Hook, aud AZ
the rate on the average, OF about one mile per
hour The water has Raritsn Bay TO fill, tending
90 turn the current in al eSstwardly direction.
and New.York Inner Bay, or Haroor, tending TO
turn part of the current 20 toe north. These are
modified, but in an incOuS deraole degree, by the