TRANSACTIONS OF THE SECTIONS. 145 



shaped sliot. The recoil is small from the absence of friction, which in rifled guns 

 amounts to from one-third to one-half the power employed. In the proposed gun 

 the only recoil is that due to the simple propulsion of the shot. An experimental 

 gun has been made on this principle, tlirowiiig a shot of 4 lb. 2 oz. 'J'he charged 

 used was one-eleventh, or G oz. of powder. The first shot was fired from H.M.S. 

 ' Cambridge,' the gunnery ship at IJevonport, at the target in the creek, a distance 

 of 1000 yards. The rotation was perfect, and the direction excellent. The gun 

 was again fired from Boviesand, Devonport, and gave a range of 2000 yards first 

 graze with the same chai-ge. Had the construction of the gun allowed a heavier 

 charge of powder, no doubt a much gi'eater range would have been obtained. 

 Further experiments were prevented by the cracldng of the gun at the muzzle. 



On the C'Jtalmers Target. By Captain Douglas Galtok, F.E.S., F.G.S. 

 The target may be understood by looking upon it as a beam, in which the top 

 flange is the front plate, the bottom flange a thinner plate behind, these two 

 flanges being kept apart by means of a web of plates at right .angles to the flanges. 

 These intermediate plates are supported laterally by layers of wood to prevent 

 their brealdng. The author stated that the results of the experiments made 

 by the Iron Plate Committee had been most successful, and showed that the prin- 

 ciple was con'ect. 



On the Electrical and Mechanical Properties of Hooper s India-rubber Insu- 

 lated Wire for Submarine C'ablex. Ihj William Hooper. 

 The author described the method by which he secures the durability of his 

 rubber. Its high degree of insulation was pointed out, and its durability under 

 very trying conditions, over long periods of time, conflrmed by experiments con- 

 ducted by Sir Charles Bright, Capt. Mallock, and others. It was stated that 

 Mr. Latimer Clark had found it unnecessary to ship Mr. Hooper's cables in water- 

 tanks ; and the Ceylon cable, now on its way out, is coiled dry. The inductive 

 capacity of Mr. Hooper's wire remains practically the same at all temperatures, 

 while that of gutta percha increases considerably at 100^ Fahr. Diagrams, repre- 

 senting the effects of pressure and immersion, were shown, from wliicli it was seen 

 that pressure improves the insulation of his wire in the same waj' as is observed 

 with gutta percha. The result of carefully conducted experiments, extending 

 over three years, proves that the absorpticjjj of water is so small that the most 

 refined electrical tests failed to discover it. 



On Rotary Engines, with special reference to one invented by W. ITall. 



By G. 0. HrGHEs, 



On recent Improvements in the Application of Concrete to Fireproof Con- 

 ^ sfructions. By Feedeeick Ixgle. 



The author pointed out what he considered a radical defect of concrete formed of 

 lime, as ordinarily used, viz. that by the action of fire it becomes reconverted into 

 lime, which, when the water from the engines is brought to bear upon it, expands 

 greatly, and forces out the walls to the destruction of the building. He advocated 

 the use of a concrete formed frorii gypsum, wliich is not liable to tliis defect. The 

 g^sum, which is of a coarse and inexpensive character, is formed into plaster of 

 JParis by roasting, and mixed with a peculiar kind of clay found in connexion with 

 the beds of gypsum. 



On a New Arrangement for picJcing up Submarine Cables. 

 By Fleeming Jenkin, F.B.S. 



This machinery was intended to limit and regulate the strain which could pos- 

 sibly be brought on a submarine cable or rope attached to it while being hauled 

 on board by the ordinary drum driven by a steam-engine. During this operation 

 it had hitherto been necessary to watch the cable carefully, regulating the speed 

 of the engine so as to keep the strain, as shown by the dynamometer, below that 

 1866. XO 



