212 REPORT — 1860. 



from those of sea navigation, shows that a totally different construction may be 

 adopted for the vessels employed. The short heavy barges with clumsily rounded 

 bows and broad sterns should be entirely abandoned. Boats of very great length, 

 compared to their breadth cf beam, may be used for cauals with considerable economy 

 of power in proportion to the cargo. The highest perfection of lines may thus be 

 attained so as to secure the smallest amount of resistance to motion, and the least 

 disturbing effect to the canal banks. For this object also a selection might be made 

 among the varieties of the screw propeller, which would obviate any lateral disturb- 

 ance of the water and drive it backwards rather than sideways. In some cases the 

 above suggestion as to the shape of boats could not be realized without lengthening 

 locks, and wherever these are numerous, jointed vessels, like those proposed for the 

 Indian rivers, might be employed. The loss of water in passing locks would be the 

 same as for a train of entirely separate boats, while the resistance to propulsion 

 would be considerably less. Steam-propelled boats thus constructed would proba- 

 bly realize the twofold result of economy in power and increase of speed to the 

 highest limit advisable for traffic in heavy goods. 



On the Longitudinal Stress of the Plate Girder. By Calcott Reilly. 



On Suggestions for an Electro-Magnetic Railway Break. 

 By Dr. B. W. Richardson. 



On the Character and Comparative Value of Gulla Percha and India~ 

 rubber employed as Insulators for Subaqueous Telegraphic Wires. By 

 S. W. Silver. 



After pointing out some of tile mistakes prevalent on the subject of the insula- 

 ting properties of india-rubber, a comparison was made by the writer between the 

 relative advantages and the insulating power of india-rubber and gutta percha 

 respectively. Insulation in the case of a submarine cable depends upon two causes 

 or properties of the bodies used : — 1. The specific non-conducting power of the 

 substance ; 2. its impermeability, by which the original insulating conditions may 

 be maintained. The insulating power of gutta percha is very high ; but, in the 

 case of a submarine telegraph cable, its porosity renders it a very imperfect insulator 

 in practice. India-rubber, with lower specific insulating properties (as would 

 appear from experiments made in dry air), is, nevertheless, practically a far more 

 efficient insulator, by reason of its complete impermeability, while in addition it 

 possesses a lower inductive capacity. It was pointed out that impermeability is as 

 important a question as specific non-conductility in an insulator of such cables ; and 

 that even if a substance could be found insulating perfectly in dry air, it still might 

 in practice be of questionable utility for submarine lines, owing to its porosity, as 

 was the case with gutta percha. There was now no difficulty in covering wires 

 with india-rubber. 



On Improvements in Iron Ship-building. By W. Simons. 



Diagonal Beams. — Each range of beams is placed in the reverse diagonal direction 

 to the range of beams, above or below it, so that collectively the vessel's beams con- 

 stitute a complete system of horizontal diagonal trussing. 



Fore and aft along the middle of each range of beams are riveted strong iron 

 clamps; and along the centre of the 'tween decks are secured in long lengths along 

 the inside of the frames, strong, angle, back-to-back iron clamps. For these beams, 

 various degrees of obliquity may be adopted ; but the angle chosen by the author (re- 

 presented in a plan which was exhibited) will probably best answer the combined 

 purpose of a beam and diagonal truss. 



It is a well-known fact that the beams, as at present placed, do not prevent the 

 straining of a vessel, but merely form a connexion between the vessel's sides and a 

 framework to support the deck. 



The hatchways and mast partners are framed in the usual manner, and the masts 

 are wedged on both the upper and lower decks. 



