100 SOME EEMAEKS ON SEWERAGE SYSTEMS. 



tight water-way. In some cases, such as passing beneath a 

 house, across streams, or in difficult ground, cast-iron pipes 

 are used, coated inside to prevent rust, and jointed with 

 lead. There is no doubt that this forms a most efficient 

 sewer ; but its cost is rather too heavy for general use. 



The foundations for sewers sometimes call forth the 

 ingenuity of the engineer. It is most important that the 

 sewer should not shift after being laid in ; and this is often 

 rather difficult to obtain in made ground or in quicksand. 

 The usual methods of forming a foundation are generally 

 adopted, such as planking, or laying faggots and then con- 

 creting above till the concrete find its bearing, etc. „ When 

 the sewer is above or near the surface of the ground, piles 

 are sometimes used. 



The other details of construction of sewers, such as tun- 

 nelling, trenching, running under heavy buildings, etc., need 

 not be gone into here, as they are common to all engineering 

 works, and have already been partially considered by this 

 Society. 



In two places in Bristol, and in many other towns, we 

 have to cross the water ; and the sewers are carried in in- 

 verted siphons laid in the bottom of the river-bed. They 

 are composed of cast-iron pipes with ball and socket joints ; 

 and, being laid with ample fall from inlet to outlet, have 

 never caused any trouble. 



With the inauguration of smaller sewers, special means 

 of inspection became necessary. This is provided for by 

 manholes, and sometimes lampholes placed alternately upon 

 the line of sewer. 



In order to afford ready inspection, Mr. (now Sir) Robert 

 Rawlinson (a Bristol man) introduced the method of laying 

 sewers in straight lines between manholes and lampholes, 

 and giving the necessary curves in the floors of the inspec- 



