484 TRANSACTIONS OF SECTION G. 



apparatus, have had as their objective the decrease in the interference caused 

 to, or suffered from, other stations. This is, at the present moment, of far 

 greater importance than efficiency. 



Since the earliest experiments in radio-telegraphy, it has been realised that it 

 is advantageous to decrease the decrement of the train of waves sent out as the 

 result of each spark. A great improvement in this respect resulted from the 

 use of the coupled aerial, and, with the exception of the spark-gap, no change 

 has been made in the sending apparatus since its introduction. The gap is either 

 stationary and subjected to an air-blast, or the electrodes are revolved at a high 

 speed with or without an air-blast. The most recent development has been the 

 use of very short gaps between copper or silver discs. These quenched-spark 

 gaps allow of much tighter coupling without the production of beats, but un- 

 doubtedly represent a great sacrifice of reliability as compared with longer gaps. 

 With the ordinary spark-gap the coupling cannot exceed seven or eight per 

 cent, without the production of beats and the consequently increased interference. 



A great improvement has taken place in the nature of the note sent out by 

 mcst large stations. In the earlier arrangements the sparks followed each other 

 so irregularly, or the spark frequency was so low, that the signal heard in the 

 telephone was nothing more than a crackling noise, very similar to, and easily 

 confounded with, the noises due to atmospheric disturbances. It is not essential 

 to tune out all other 6ignals and extraneous noises, if the signals which have to be 

 received have a distinctive musical note. This has led to the frequency being 

 increased from ten or twenty to five hundred or a thousand sparks per second. 

 The difficulty of getting, with any regularity, a thousand sparks per second with 

 an ordinary gap and a power of several kilowatts will be apparent. If the use of 

 a certain note became general, much of its advantage would be gone, but it would 

 still be a great improvement in combating atmospherics. 



Although the receiving arrangements have been made very convenient for 

 rapid tuning, no radical change has been made in the detectors employed. One 

 has still to choose between reliability and sensitiveness. If extreme sensitiveness 

 is not desired, the magnetic detector is ideal in its simplicity. For the reception 

 of weak signals we have the Fleming valve, the electrolytic and various crystal 

 detectors, if necessary, in conjunction with the Brown telephone relay. Attempts 

 have been made to obtain selective working by tuning the reed of the relay, 

 but the general utility of the station so equipped would be greatly reduced, to 

 say nothing of the adjustment and manipulation required. 



2. Portable Equipment for Wireless Telegraphy. 

 By Captain H. Eiall Sankey. 



TUESDAY, SEPTEMBER 5. 



The following Papers were read :— 



1. Economical and Reliable Power Generation by Overtype Superheated- Steam 

 Engines. By W. J. Marshall. 



The steam engine is the oldest of all prime movers developing power from the 

 combustion of fuel, and it is undoubtedly the most flexible and reliable. Of late 

 years the internal-combustion engine, on account of its high thermal efficiency 

 and consequently low fuel cost, has attracted the attention of power users very 

 considerably. The effect of this has been to cause steam-engine makers to 

 devote their attention to' producing an engine or complete steam plant which 

 will have a fuel economy on a par with that of the internal-combustion engine. 

 This object has been achieved by very careful designing and arrangement of the 

 component parts of a steam-engine plant with a view to reducing the fundamental 

 losses occurring in such a plant to a minimum. The result is the modern over- 



