MAY 19, 1923 PROCEEDINGS: PHILOSOPHICAL SOCIETY 219 
881ST MEETING 
The 881st meeting was held in the Cosmos Club Auditorium on Saturday; 
March 24, 1923. It was called to order by Vice-President Hazard with 50 
persons in attendance. 
Mr. J. Pawuine presented a paper on The 9” Transit of the U. S. Naval 
Observatory and its work. The paper was illustrated with lantern slides 
and was discussed by Dr. Humpureys. 
Mr. H. A. Marmer presented a paper on The tidal phenomena in New York 
harbor. ‘The paper was illustrated with lantern slides and was discussed 
by Messrs. HumpHrReys and Gisu. 
Author’s abstract: In New York Harbor the tidal and current phenomena 
exhibit more than usual variety because of two geographic features that 
distinguish the harbor: (a) Unlike other harbors which generally consist 
of a tidal bay or river New York Harbor comprises a system of five tidal 
highways that connect with the open sea by means of two inlets many miles 
apart; (b) the waterways forming the harbor—Upper Bay, Kill van Kull, 
East River, Harlem River and lower Hudson River—are either intercom- 
muricating or lead into other bodies of water. 
In Upper Bay and in the lower Hudson the tidal and current phenomena 
are typical of those found in bays and rivers in which the tidal movement 
is of the progressive-wave type. The time of tide becomes later in going 
up stream at a rate dependent on the depth, the formula being approximately 
r = gd, where r is the rate of advance, g the acceleration of gravity and d 
the depth of the waterway. The mean range of the tide decreases in going 
upstream, and the strength of current comes about the times of high and 
low water. 
In the East River, the tide changes by 31 feet through the stretch of 14 
geographic miles but not at a uniform rate. The range of tide is 4.4 feet at 
the eastern end and 7.2 feet at the western, but in the river near the western 
end is a region with a range of 4.0 feet. The strength of the current is very 
nearly simultaneous throughout the river. 
It has been customary to ascribe the tidal and current phenomena in the 
East River to the interference of two tide waves, the one coming from Long 
Island Sound and the other from Upper Bay. But these phenomena can 
easily be derived by considering the matter from the hydraulic point of view 
and a slope-line diagram brings out the principal tidal and current pheno- 
mena immediately. 
The tidal and current phenomena in the Harlem River and in Kill van 
Kull, as in the East River, are conditioned by the fact that the tidal move- 
ment in these waterways is largely of the hydraulic type. 
A brief description was given of a bifilar suspension direction indicator 
used in determining the direction of subsurface currents. 
Dr. F. E. Wricut presented a paper on Methods for distinguishing 
between natural and cultivated pearls. Specimens of both natural and 
cultivated pearls were exhibited, and the paper was discussed by Messrs. 
TucKERMAN, Ives, Rupr, and Humpureys. 
Author’s abstract: The cultivated pearl from Japan consists of a center 
or nucleus of mother-of-pearl] or of an inferior pearl, on which thin concentric 
shells of pearly substance have been deposited by the shell secreting epider- 
mis of the pearl oyster; it differs from the normal fine pearl of commerce 
only in the fact of its foreign nucleus; the fine pearl consists of the thin 
concentric shells of the pearly substance throughout. Amy method for 
