284 CJironicIes of Science. [April, 



plugs, and this, breaking the vacuum, causes the hells to fail into 

 gear. 



That the pneumatic principle possesses many advantages over 

 the other two, both as to certainty of action and from its non- 

 liability to be tampered with, is beyond a doubt : but the Com- 

 mittee of Eailway 3Ianagers have nevertheless recommended the 

 rope system, probably on account of its cheapness, and their recom- 

 mendations have been accepted by the Board of Trade. 



The anticipated difficulties attendant upon the location of the 

 great floating-dock recently constructed in this country for Ber- 

 muda, in consequence of the insufficient depth of water at the 

 selected site, has led to a proposal by Messrs. Gwynne & Company 

 for the use of a hydraulic dredger for the purpose of increasing the 

 dejDth of water where the dock is to be finally moored. The prin- 

 ciple upon which this dredger is constructed is based upon the , 

 fact that sand or other loose earthy material can be freely passed 

 through a centrifugal pump, when mixed with water, in the same 

 manner as the water itself is passed through it. If the sand to be 

 dredged can be well stirred up and the jjump be placed under 

 water and close to the sand itself, the rapid removal of the latter 

 is certain ; and Messrs. Gwynne's idea is therefore to get their 

 pump to work down at the very bottom, to stir up the sand 

 mechanically, and to conduct all that is so stirred up directly into 

 the pump itself. It would then be driven up a wrought-iron pipe, 

 to the bottom of which the pumj) is fixed, and dehvered in a stream 

 into a barge. 



Few i)eople could form any idea, at the first introduction of 

 Gifiard's Injector, which has now so generally taken the place of 

 donkey-pumps for feeding boilers, what an important j^art the 

 principle involved in its construction was likely to play in the 

 economy of steam-engines generally ; and even now one would be 

 scarcely justified in assuming that the extent to which it is 

 applicable has been fully realized. Testimony has been ainply 

 and repeatedly borne to the correctness of the principles of its 

 construction, but the extent of its economical results is, perhaj)S, 

 not so widely known as might be. Professor Henry Morton, in 

 the course of a paper recently communicated to the Journal of the 

 Franklin Institute, stated, "That the entire force which passes 

 from the boiler in the issuing steam is returned to it, with the 

 exception of that expended in lifting and injecting the feed-water, 

 and so much as is lost by radiation of heat from the various parts 

 and connections." M. Ch. Combes, Inspector-General and Director 

 of the Ecoh des Mines, says that the Injector is " without doubt 

 the best of all those hitherto used for feeding boilers, and the best 

 that can be employed, as it is also the most ingenious and simple," 

 and he further adds, " it is theoretically perfect." 



