Proceedings of the Polytechnic Association. 1\1 



piston and cylinder head to be nearly in contact, and even this space 

 is filled with water so as to bring them still closer together. 



XJndekgrouxd City Kail ways. 



The discussion of this question was resumed. Mr, Gardener was 

 accorded the floor and occupied some considerable time in a repeti- 

 tion of his remarks made at the meeting of the previous week, and 

 then, by the aid of drawings, illustrated the means which it is designed 

 to employ to prevent any material interruption of travel on Bi-oad- 

 way during the operation of constructing the Arcade railway, the 

 apparatus consisting in a sectional bridge, apparently intended to be 

 placed over the excavation while the work therein is in progress. 

 The question of the deleterious effects of the gases from the locomo- 

 tive being called up, Mr. Emory stated that in his opinion no steam 

 locomotive could be employed to advantage in an underground rail- 

 way. 



After Mr. Gardener had finished the elucidation of his ideas rela- 

 tive to the Arcade plan, Mr. Barnum, in a style no less diffuse, set 

 forth his project of an elevated railway, taking the gi'ound that the 

 city railways should be built, not on Broadway, but on tlie avenues, 

 in order to better accommodate the great mass of the population. 

 His idea appeared to include the use of corrugated wrought iron 

 posts, supported upon cast iron bedsills buried in the ground, the 

 columns being provided at the top with iron crossheacls, having 

 placed upon them the wooden crossties to which the rails are to be 

 secured ; there being, furthermore, pads of india rubber interposed 

 between the crossheads and the ties. In addition to this, Mr. Barnum 

 proposed to have a pneumatic tube arranged between the rails for 

 purposes of postal dispatch, and claimed, as some of the ad'vantages 

 pertaining to his mode of construction, that the supporting posts 

 would furnish a very convenient means of suspending signs and 

 awnings. 



After agreeing to resume the question, the association adjourned. 



June 4, 1868. 



Prof. Tillman said the President of the Institute, the Hon. Horace 

 Greeley, had consented to occupy the chair during the I'eading and 

 discussion of the usual summary of scientific news, Mr. Greeley 

 assumed the duties of presiding oflicer with the evident approbation 



