MECHANICS AND USEFUL ARTS. 95 



larboard side of the dam, was carried under its bottom and rendered 

 up on to the starboard side of the main deck, and vice versa in re- 

 spect to the other cable. From the ends representing the bow and 

 stern of the dam there also ran large hawsers which kept it from 

 going adrift in either of those directions. Power was then applied, 

 and the wooden crib hove up against the ship's bottom. Around the 

 parasitic structure were then carried other hawsers and cables, until 

 it was firmly secured in place. Thus far matters progressed favora*- 

 bly the dam was in its place, but it was full of water. Two huge 

 chutes, or funnels, which pierced the sub-aqueous box on one side, 

 ten feet from the ends, ran up a short distance above the water-line, 

 and furnished the means of reaching the fracture. The edges, or 

 gunwale of the dam, must, as will be apparent, be made water-tight, 

 else the pumping might be ^continued indefinitely without any result. 

 This it was proposed to accomplish by means of some elastic material ; 

 hence India-rubber, flock mattress, or substances of a like nature, were 

 suggested for the purpose, but, not being available, a plan of the en- 

 gineers, Messrs. Renwick Brothers of New York, was put in force. 



It occurred to them that a water-hose would be just the thing. 

 After the details of its construction for which we have no room 

 had been worked up, it was soon applied, and fulfilled all the expec- 

 tations formed of it. No sooner was the means discovered for obvi- 

 ating one trouble, however, than another appeared. This latter vex- 

 ation was caused by the difficulty of overcoming the tendency which 

 the hose had to draw in under the compartment. In order to secure 

 it, strips of canvas were attached to one of two battens which armed 

 the gunwale dam; these were carried under and over the hose at 

 intervals in such a manner that the latter lay in the bight of the for- 

 mer ; the flying end was then fixed to the batten again. Upon the 

 outside of the case, or dam, a lappet of Brussels carpet was secured, 

 which the water kept up against the Great Eastern's bottom, aiding 

 materially in keeping the sea out ; weeds were also thrown into what- 

 ever crevices might remain, and the projectors of this ingenious method 

 were rewarded for all their time and trouble by its complete success. 

 To all the unequal surfaces the water-hose opposed its soft and elas- 

 tic surface, filling up cavities which could not be effectually closed by 

 any other means. The pumps were again tried, and the crib was 

 pumped dry. When this consummation was attained, workmen de- 

 scended the chute, and in a comparatively short time replaced the 

 plates in a substantial manner. 



STRENGTH OF STEAM BOILERS. 



The secretary of the Manchester (Eng.) " Association for the Pre- 

 ve'ntion of Steam Boiler Explosions" in a recent report makes the 

 following remarks on the method of ascertaining, from time to time, 

 the strength of boilers in use. He says : 



" I know no means of ascertaining the sufficiency of the original 

 construction of a boiler, or of testing the weakness produced upon it 

 by wear and tear, in short, of testing either new or old boilers, 

 equal to the use of hydraulic pressure, and think all steam-users 

 would do well to make systematic use of this test once a year. In 



