Proceedings of the Polytechnic Association. 949 



accommodate a few ships that go to the docks above it or to the navy 

 yard. Large warehouses might be constructed on either side of this 

 bridge, opposite to and connected with the piers, which would greatly 

 accommodate shippers, and the rent of which would go far toward 

 paying the interest on the cost of such a bridge. 



It will be remembered that the first plan for a truss bridge over 

 East river was exhibited and explained before this association by 

 Mr. Alfred P. Boiler. (See Transactions for 1866-67, pp. 893-907.) 



Should the plan for making a ship channel from Jamaica bay to 

 Flushing bay on the Sound, as proposed by the chair at a former 

 meeting (see Transactions of 1867-68, p. 817), there could be no 

 objection to having a number of bridges between ISTew York and 

 Brooklyn. The vast area of land, on the Brooklyn side, within ten 

 miles of our City Hall, which is still unoccupied, would accommodate 

 several million inhabitants ; but it will not be occupied by men doing 

 business in New York, unless it is made more accessible by means of 

 bridges. 



Dr. J. J. Edwards said: The subject of piers and bridges in the 

 East river had been discussed lately, with ability, by a writer in the 

 lieio Yoi'l' World. In the year 1900 this great metropolis will have 

 5,000,000 of inhabitants, if we include those in the suburbs of ISTew 

 York ; and some provisions must soon be made for the great increase 

 of population on the other side of the East river. If this river was 

 closed, or nearly so, there would be a great addition to the area of 

 " made land." In this event the Harlem river^ could be deepened, 

 so that ships could find their way from the N^orth river to the Sound. 



After further discussion, it was decided to resume this subject at 

 the next meeting. 



^ Adjourned. 



January SI, 1869. 



Professor S. D. Tillman, Chairman ; Mr. C. E. Emery, Secretary. 

 The chairman read the following notes on science : 



Leather Collodioj?. 



Carbon prints are now made by some French photographers on 



what is technically called " leather collodion," consisting of collodion 



films to which strength and elasticity have been given by the addition 



of castor oil. These films are so extremely thin as to permit exposures 



