666 REPORT— 1882. 



MONBA Y, A UG UST 28. 

 The following Papers were read : — 



1. On Compressed Air as applied to Locomotion. 

 By Sir Frederick Bramwell, F.B.S. 



This paper consisted of a description of a tram-car on the Mekarski system now 

 employed at Nantes in France. A car on a similar system is bein»' constructed for 

 trial on the tramway running from Kings Cross to Ilolloway. The gauge of the 

 French line is 4 feet 8-h inches, the wheel base of the car being 5 feet 9 inches. The 

 principal features of the engine consist in the use of what is termed a ' hot pot,' 

 and in an automatic regulating valve. The hot pot is a receptacle containing hot 

 water and steam under pressure, and through tliis the compressed air is allowed to 

 bubble on its way from the receivers to the cylinders, so that it may be expanded 

 in the cylinders without risli of the formation of snow. The automatic regulating- 

 valve is set on the top of the hot-water vessel. A hand-wheel lowers or raises a 

 plunger ; this acts upon the liquid contained between an elastic india-rubber dia- 

 phragm placed a little below the plunger and the upper part of the vessel. Just 

 around the plunger there is an annular air-space acting as an air-vessel. When 

 the plunger Ls depressed into the liquid, the result is to compress the air in the air- 

 vessel to any desired extent. Then, as the hot pot is always in connection with the 

 reservoirs in wliicli the compressed air is contained, when the outlet air cock on 

 the regulating valve is opened, air bubbles through the hot water and rises past 

 the cone valve which is attached to the diaphragm, and presses on the under side 

 of the diaphragm, tending to raise it ; but it cannot succeed in doing so until the 

 pressure of the air below the diaphragm equals that in the annular air-vessel 

 above, and thus tlie pressure in the annular air-vessel is automatically the measure 

 of the pressure that will prevail in the engines. So soon as this is exceeded the 

 diaphragm rises and closes the \iilve ; and so soon as it falls the air in the annular 

 air-vessel re-expands, presses down the diaphragm, opens the conical valve, and 

 lets in more compressed air. The dri^ er is thus enabled to vary the pressure, while 

 the pressure, whatever it may be, is maintained steady, whether the engines are 

 running fast or slow. 



The working of the engines was very satisfactory. There was no smoke, no 

 escape of the steam, no noise. The exhaust air is let into a box, from whence it 

 escapes quietly just above the level of the road. So far as can be judged from 

 outside appearance there is scarcely anything to distinguish one of these cars from 

 an ordinary horse tram-car. The compressed air reservoirs are charged at one end 

 of the journey. For this purpose four horizontal condensing steam-engines are 

 used, each of about 20 nominal horse-power. Each engine works two single- 

 acting air-pumps. The first air-pump compresses to six atmospheres, the second 

 draws from the first and compresses to thirty. While the compressed air is being 

 charged into the receivers, steam is turned into the hot pOt, so as to heat the water, 

 a certain quantity of the \\-ater being, wlien necessary, allowed to run out. Ac- 

 cording to information given to the autlior, it appeared tliat the cost of working 

 the line on this system was less than the cost of horse-power, and the system had 

 besides several other advantages. 



2. Recent Progress in Telepliony. By W. H. Preece, F.B.S. 



This paper gave an account of the progress made in the construction of tele- 

 phonic apparatus since the telephone was introduced to the British Association in 

 1877. The author described the principal forms of telephone receivers and trans- 

 mitters, including those of Ader, Gower, Dolbear, Edison, Blake, and others. He 

 also described the arrangements which have been made to diminish induction on 

 busy lines, and thereby to get rid of tlie noise which is the chief difficulty in trans- 

 mitting articulate speech. The only really successful plan was that of employing 

 a complete metallic circuit instead of using the earth for the return circuit, and 

 twisting together the two wires composing this circuit. In concluding, the author 



