Proceedings of the Polytechnic Association. 757 



influence (wlietlier heat, light or gravitation), acts as a controlling 

 agent. 



The Chicago River Tunnel. 



This river suhway is intended to prevent the interruption of land 

 travel which is now caused by the passage of vessels. The whole 

 shipping of Chicago is harbored in a narrow river, and a single vessel 

 passing from the upper to the lower end of the harbor recpiires the 

 opening of the draws in fifteen different bridges. Nearly all vessels 

 must pass through the first or lower bridge, consequently the inter- 

 ruption is greatest in the most busy part of tl^e city. Acting on the 

 suggestion of E. S. Cheeseborough, the city authorities decided to 

 construct a crossing under the river, which was commenced in 1866, 

 and is now rapidly pushed forward. It will connect East and West 

 "Washington street, and extend a distance of 1,605 feet, only 200 feet 

 of wliich is directly under the river. The western approach is 773 

 feet long, with a descent of one foot in eighteen and a half feet ; the 

 eastern is 622 feet, with a grade of one in twelve. The river portion 

 of the tunnel is divided into two arches, and under each is a carriage 

 way, eleven feet wide. The intermediate wall is tM^o feet thick, and 

 contains eleven openings. Tlie side walls are five feet thick, consist- 

 ing of one foot of concrete backing, two feet eight inches of stone, and 

 one foot four inches of brick lining. All arches are built with inverts 

 one foot eight inches thick, bedded upon two feet of concrete. The 

 top of the structure is fourteen feet four inches below the mean lake 

 level, and three feet below the restored bed of the river. An inter- 

 mediate wall separates the sidewalks from the roadway, and in 

 recesses at short distances, lamps will be placed to light both. In the 

 approaches to the tunnel proper the two arches are merged into one, 

 nineteen feet six inches wide, by fifteen feet nine inches higli, the 

 sidewalk being in a separate tunnel. For the purpose of drainage at 

 the lowest point of the tunnel, in the center of the river, a sump is 

 formed communicating witjii another sump outside of the tunnel, and 

 just within the river quay, from which the drainage is pumped into 

 a high level sewer. Should this tunnel prove a success, similar 

 structures will be made to connect all the main streets leading to 

 the river. 



Chemical Changes. 

 M. A. Yernon Harcourt, of London, closes a paper " On the rate 

 at which chemical actions take place," with the following propositions 



