756 BEPORT— 1894. 



one-half. The percentage of steam present in the mixture during expansion was 

 also increased bj' about 50 per cent. 



Throughout these experiments an increase of economy with the hotter walls 

 was always verified ; the thermal efficiency was higher, the initial condensation 

 less, and the percentage of steam present during expansion always increased. 



The tests on this engine point to the practical conclusion that the range of 

 steam temperature in the cylinder per stroke has much less efi'ect on the steam 

 consumption than the temperature of the walls. 



The paper may he shortly summarised thus : — The most uneconomical results- 

 were always obtained with the cylinder walls colder than the entering steam. 

 Under these conditions considerable initial condensation was produced, drops of all 

 sizes up to 3 mm. diameter being formed and running down the cold surfaces. 

 The heat also penetrated into the colder walls to a considerable depth, a certain 

 quantity being given up by the steam at every stroke, to raise the temperature of 

 the internal surfaces alter exposure to the condenser temperature. Both at cut-off 

 and release there was a great deal of water in the cylinder compared with the 

 weight of steam present. On the other hand, the most economical results wer© 

 always obtained when the cylinder walls were at about the same temperature as 

 that of the entering steam. Under these conditions the rate of initial condensa- 

 tion was very much lower, and the drops of water formed much smaller in size. 

 The heat penetration into the walls was also mucbless, a smaller amount of steam 

 sufficing to heat the internal surfaces after being cooled by the condenser. The- 

 percentage of steam present in the mixture, at cut-off and release, was also very 

 much increased. 



If engineers and others using steam engines wish to work economically and 

 with smaller boilers, they must arrange to keep their cylinders and covers as hot as 

 the steam entering the cylinder ; otherwise the cylinder becomes unintentionally- 

 an efficient condenser, with a large area of cooling surface. 



Properly applied steam jackets are economical, because they raise the tem- 

 perature of the walls touched by the steam. Those who cannot steam-jacket 

 the whole cylinder should at least jacket the two covers, which are the most 

 important surfaces. 



Well-arranged jackets with proper-sized pipes for entering steam and exit water, 

 without places for air to collect, are an excellent investment, and pay a good 

 interest on the small additional cost. 



MONDAY, AUGUST 13. 

 The following Papers were read ; — 

 1. On Signalling through Space. By W. H. Preece, C.5., F.R.S. 



2. On Some Advantages of Alternate Currents. 

 By Professor Silvanus P. Thompson, F.R.S. 



3. Continuous-current Distribution of Electricity at High Voltage at Oxford, 

 By Thomas Parker, F.R.S.E., M.Inst.C.E., M.Inst.M.E., M.Inst.E.E. 



Tlie Central Station at Oxford was started in the middle of the year 1892, and 

 is equipped witb high-tension continuous-current dynamos driven by means of belts 

 from triple-expansion vertical engines ; it is placed 1,500 yards away from the area 

 of lighting. The current is distributed by means of a network, which is fed by 

 motor generators transforming from 1,000 to 105 volts. These motor gene- 

 rators are started, stopped, and regulated from a central switch station placed in 

 the area. The main feature of the system is the complete control of the motor 



