878 KEPOET— 1893. 



as tefore stated, reduced at the centre, leaving a collar on each end. The inside 

 edges of these collars form the cut-off edges for pressure, while the outside edges 

 govern the exhaust ports. When the piston is in its central position in the cylinder, 

 there is a dead point for pressure and exhaust. But when the piston rests on the 

 end of the chisel, and the tool is pressed up to its work, the inlet port is opened on 

 the front side, and the exhaust port at the hack end of the cylinder. Therefore, when 

 the exhaust trigger valve is opened, a load of about seventy times the piston's mass 

 acts on the end of the piston, and sends it at an enormous velocity, which carries 

 it over the dead point until it is cushioned at the back end of the cylinder, and 

 similarly on its return stroke until it hits the chisel head. 



The tool also works equally well with steam, special provision being made to 

 prevent the heat of the steam from inconveniencing the workman. The tool is 

 now largely used for calking, and it has been applied with success to the operations 

 of chipping and dressing plates and castings. 



It is also capable of boring a 1-in. hole through sandstone at the rate of about 

 12 in. per minute, and through whinstone at about 4^ in. per minute. 



It is largely used by many of the leading railway companies, engineers, and 

 shipbuilders throughout the country. 



MONDAY, SEPTEMBER 18. 



The following Papers were read : — 



1. On the Relative Cost of Conductors with Different Systems of Electric 

 Poioer Transmission. By Gisbeet Kapp. 



Owing to difficulties of insulation and flashing at the commutator, long-distance 

 transmission of power by continuous current is not so practicable as by alternating 

 currents, where the generating and receiving apparatus can easily be insulated to 

 any desired degree. The working pressure is thus limited, not by the apparatus at 

 either end, but by the difficulties of insulating the line, and in comparing various 

 systems of power transmission it is necessary to place all on an equal footing as 

 regards stress on the insulation of the line. Taking a transmission plant with 

 continuous currents as the standard of comparison, and assuming in all cases the 

 same distance, total power, efficiency, and safety against breakdown of the insula- 

 tion, the author finds that the single-phase two-wire system of transmission by 

 alternating currents requires double the weight of copper as compared with con- 

 tinuous currents. The same ratio applies to the double-phase alternating current 

 sent over four wires, but if the system is worked with a common return (i.e., em- 

 ploying only three wires), the weight of copper is increased to 2'9 times that of 

 the equivalent continuous current system. This increase is due to the fact that by 

 tying two of the conductors together the absolute potential between the other two 

 and between either and earth is increased, and to get back to the original condition 

 of stress on the insulation the working pressure has to be lowered. With the three- 

 phase three-wire system the weight of copper is only 1'5 time that of the equi- 

 valent continuous current system, showing that as regards economy of copper the 

 three-phase system has an appreciable advantage over the single and the two-phase 

 systems. 



2. On the Utilisation of Waste Water-power for Generating Electricity. 



By Albion T. Snell. 



On the Continent water-power is extensively used for driving electric plants, 

 but in Great Britain, for a similar purpose, power is usually derived from the 

 combustion of coal. 



This difference in practice is partly the result, no doubt, of the relative supply 



