622 TRANSACTIONS OF SECTION G. 
constitute one oscillating system of a low frequency, to correspond to an ordinary 
commercial alternator which excites them. When the swing is worked up they 
burst through the spark gap, short-circuiting out the Ruhmkorff and giving ex- 
cessively rapid oscillations, which are the ones transmitted. These are picked up 
by the receiving station and are transferred at constant frequency into a closed air- 
condenser circuit, which, when its swings reach a maximum, overflows into the 
coherer. This is called the ‘overflow method,’ and was described by me in 1889 
and 1891. 
Ratio of Received to Emitted Energy. 
Theoretical calculation shows that the energy received, compared with energy 
radiated, depends on the cube of the linear dimensions of emitter and receiver, if 
they are alike, and likewise on the cube of the distance between them. 
Measurements made with the radio-micrometer confirm this estimate approxi- 
mately, the value in one series of experiments being 10-°. Although this is a small 
fraction, the accuracy of tuning is such that messages are sent between Burma and 
the Andaman Islands—a distance of about three hundred miles—with less than a 
horse-power. 
Other Precautions. 
To get such a result, precautions must be taken to avoid damping out the 
oscillations, not only by elevation even of the lower aérial above the earth, but 
by using appropriate conductors for these excessively high frequencies. To this 
end the wires are finely subdivided into insulated strands, and consist of a great 
cable or bundle of thinly insulated No. 40 wires, and the various self-inductions 
and other arrangements for effecting tuning are similarly wound. The tuning 
capacities are also arranged so as to be continuously adjustable, without pegs or 
discontinuities ; and every kind of broken or uncertain contact is scrupulously 
avoided. 
3. Note on Oscillograph Study of Duddell Arcs of Low Frequency.' 
By J. T. Morris. 
4. Developments in Electric Incandescent Lamps.? By Leon GASsTER. 
5. The new Engineering Laboratory at the City and Guilds of London 
Institute, Finsbury.2 By Professor E. G. Coxer, J.A., D.Sc. 
The recent extension in the Department of Mechanical Engineering at the 
City and Guilds Technical College, Finsbury, has been provided for by the City 
Companies aided by a private donor. ; } 
A new wing has been added to the College, in which accommodation has been 
found for an engineering laboratory, drawing-offices, lecture and preparation 
rooms. The principal feature of interest is the engineering laboratory, of about 
4,000 square feet in area, on the basement floor. A part of this laboratory has 
been devoted to hydraulic equipment, which is mainly grouped with reference to 
a cast-iron channel, 80 feet long, and of square section 2 feet side. At one end 
of this is a space for a vertical pressure cylinder, for experiments on jets, impact 
on vanes, and the like. At the other end are measuring tanks, of a total capacity 
of 3,500 gallons, into which the water drains after passing over a weir in the 
main channel. There are also two subsidiary channels, parallel to the main one, 
and draining directly into the measuring tanks. The water after use is raised to 
1 Published in Electrical Review, August 9. 
2 Published in Electrician, August 23. 
3 Published in ewtenso in Engineering, August 16. 
