L. MECHANICS AND ENGINEERING. 467 



THE CONSTRUCTION OF REVOLVING DRAWBRIDGES. 



Mr. Clemens Herschell has presented to the American 

 Society of Civil Engineers a paper on the principles of the 

 construction and calculation of the strains in revolving draw- 

 bridges, and his work has an important value as one of prac- 

 tical interest to the profession of engineers. The calculation 

 of continuous girders was first undertaken by Navier in 1830, 

 but was much improved upon by M. Classeyron in 1857. 

 These and other authors have, however, Mr. Herschell states, 

 developed only special cases, and he has undertaken to de- 

 velop the equations for the general case of unequal spans 

 and supports, either in or out of level. Following the equa- 

 tions oriven in a recent work of Wevranch, Mr. Herschell 

 gives in detail the formulae necessary to compute the dimen- 

 sions of every part of the bridge in question, and illustrates 

 the whole by numerical examples. The several equations 

 are written out in full, and are so clear as to enable any one 

 to follow the processes with ease. A couple of tables, show- 

 ing the strains experienced by every jDortion of a bridge 

 under certain loads, gives a very lucid view of the I'elative 

 strength demanded in the various portions of the structure. 

 Transactions American Society of Civil Engineers, March, 

 1875,395. 



THE PROPER CONSTRUCTION OF SEWERS. 



A report has lately been made by a committee of eight 

 of the most eminent civil engineers and professors of Great 

 Britain to the British Association for the Advancement of 

 Science on the subject of the treatment and utilization of 

 sewerage, which contains very valuable suggestions as to the 

 proper construction of sewers. These suggestions are the 

 more worthy of careful attention from the fact that not 

 only are our city sew^ers at the present time badly construct- 

 ed and of indifterent materials, but, in addition, there appears 

 to prevail a mistaken and dangerous idea that it is better to 

 build with loose joints, in order to allow of the percolation 

 of the sewer contents through the subsoil. The importance 

 of an intelligent and authoritative utterance upon these 

 points is vastly more pressing at the present day than ever 

 before, since the practice of connecting water-closets with 



