TRANSACTIONS OF THE SECTIONS. 185 



sheets, which are again divided into tapes. After the tapes have been wound round 

 the wires, they have usually been consolidated by heat, or by the use of solvents, both 

 of which are injurious by their tendency to favour oxidation. Wires thus insulated 

 give good results for a short time, but their efficiency is soon destroyed. The re- 

 sults obtained with five specimens of india-rubber-covered wire supplied by different 

 manufacturers for experimental purposes to the Government of India, and sent out 

 to Kurrachee in 1863, were adduced by the author, and showed that four out of the 

 five were defective after submersion in the Indian Ocean, the one only, supplied by 

 himself, remaining perfect. In insulation this specimen was the highest yet at- 

 tained, and the perfection of the joints was fully proved. The central position of 

 the conductor was unaltered by any elevation of temperature, and its insulation re- 

 mained good up to 150° Fahrenheit, and even higher temperatures. The mechani- 

 cal properties of the core devised by the author, were also shown to surpass all other 

 materials yet produced. The importance of the low inductive capacity of the wires, 

 insulated by the author's process, was dwelt upon. Sir Chas. Bright, Mr. Latimer 

 Clark, and Professor Thomson, had made independent investigations into the capa- 

 bilities of the wire thus insidated, and the results deduced by those gentlemen were 

 singularly in accordance with each other, the two former giving the induction of the 

 author's wire compared with gutta percha as 100 to 136, the latter as 100 to 135. 

 The rate of signalling being proportionate to the retardation arising from induction, 

 the value of the process, in a line of such length as the Atlantic cable, would be 

 at once apparent in a commercial as well as a scientific view. The Government 

 have since ordered three lengths of 50, 40, and 45 miles of this insulated wire, which 

 are now en route for India. 



Machinery for compressing Air, and the Applicability of such Compressed Air 

 for working Coal-cutting and other Underground Machinery. By T. 

 Levick. 



The advantages which the paper described were: — 1. The simplicity of con- 

 struction, and small cost. 2. The small amount of power to overcome the friction 

 of the moving parts. 3. It was not affected by the production of heat in the com- 

 pressed air. 4. It acted as a regulator, adapting its speed to the consumption of air 

 underground. 5. Being used at the mouth of coal-pits, the additional loss of 

 power was not of so much consequence. 6. The small amount of space occupied. 

 The paper explained that the air compressed by the engine at the mouth of the 

 pit was conveyed to the machinery underground in 4-inch cast-iron pipes, carried 

 along the main-headings, from which the compressed air was conveyed in 1 J-inch 

 gas piping, connected with the machine in the pit by an india-rubber hose. The 

 prominent feature of the machine is a pick, which digs the coal when the engine 

 at the mouth of the pit is in motion. The pick can be worked at any angle at 

 which the coal may lie, and can be easily put to work at any part of the thickness 

 of the coal, whether it might be desired to " hole " in the bottom or at the top of 

 the measure, or at a parting in the middle, or any other portion of it, by simply 

 shifting the pick to a greater or less distance upon the axis on Avhich it is keyed. 

 The machine moves forward as the work progresses by means of a hand wheel, 

 which communicates motion by bevel wheels to the wheels upon which the ma- 

 chine travels. In cases of bad roof, the use of the coal-cutting machines had been 

 objected to on account of the distance required (between the face of the work 

 and the supports to the roof) for the back work of the pick. Another objection 

 was that the work had to be passed over twice or three times, in order to gain 

 the required depth of cut. These objections have been obviated by the machines 

 introduced to notice, by which the stroke of the pick, when making its cut, was 

 from the back of the cut towards the face, instead of passing across the road and 

 striking into the face in the direction observed heretofore. By this means the 

 supports to the roof could be brought close up to the road ; the concussion of the 

 blow was reduced ; and about six inches of the coal had not to be cut, it being 

 forced out as the pick approached the face. The quantity of compressed air con- 

 sumed by each coal-cutter was determined from some indicator diagrams to be 327 '6 

 cubic feet per minute, at 30 lbs. pressure. The machine was working at 08 strokes 



