L. MECHANICS AND ENGINEERING. 497 



it is evident that analogous conditions will prevail, and it 

 will eventually be necessary either to resort to dredging or 

 to adopt Cialdi's recommendation. 



In his work on the Mediterranean ports, Cialdi has sought 

 to determine the principal dimensions of the port that shall 

 have a given annual tonnage. His formulas permit him to 

 calculate very nearly the development of the quays and sur- 

 face of the harbor, and that of the outer harbor or roadstead. 

 As to the mode of construction, he discusses the relative 

 convenience of systems whose foundations have solid stone 

 blocks or loose masses. The latter has been often employed 

 in France, especially for the moles at Cherbourg and the jet- 

 ties of Marseilles and Algiers, where, in order to oppose the 

 formidable action of the ocean, blocks of nine hundred cubic 

 feet have been employed. This method has the inconvenience 

 of requiring considerable time before the mass has entirely 

 settled. This has been avoided in the construction of the 

 port of Dover, in England, by placing the blocks in a regular 

 position under the water by the aid of the derrick. In his 

 plan for developing the harbor of Civita Vecchia, one of the 

 most important commercial ports of Italy, Cialdi proposes to 

 combine the two systems by employing two moles and a 

 breakwater. At present this port has a jetty arranged like 

 the grand dike of Cherbourg, allowing two entrances, so 

 that, according to the prevailing wind, a ship can choose 

 either the one or the other. 13 B, III., 198. 



THE EYAPOEATION OF WATEE IX STEAM-BOILEES. 



A number of experiments have been made by the engi- 

 neers of the Northern Railway of France on the evaporation 

 value of the different parts of a locomotive boiler divided 

 into five compartments. Each compartment held seventy 

 gallons of water, and was fed from a gauged tank by a 

 special pump. The compartments themselves comprised 

 the fire-box and four other smaller sections of tubing, each 

 of them three feet long, w T ith one hundred and seventy-nine 

 square feet of surface, while the fire-box has seventy-seven 

 square feet of surface. The results confirm the fact, already 

 established by Williams and by Graham, that the evapora- 

 tive performance of the tube surface diminishes rapidly with 

 the distance from the fire-box. Havrez, by careful analy- 



