468 SECTIONAL TRANSACTIONS.—G. 
15. Mr. T. M. Newastu.—Description of Work in progress at Glad. 
stone Dock. ‘ 
16. Report of Committee on Complex Stress Distributions in Engi- 
neering Materials. (See p. 345.) 
17; Prof. E. G. Coxrer, F.R.S.—A Comparison of Eaperimental 
Methods for obtaining the Stress at a Point in a Plate by Optical 
and Mechanical Methods. 
In the afternoon the new Gladstone Dock Works of the Mersey 
Docks and Harbour Board were visited. 
Wednesday, September 19. 
18. Prof. E. W. Marcuant and Mr. T. H. Turney.—On a Method of 
Improving the Shape of the Voltage Wave of Alternators by 
External Means. 
This paper describes an arrangement of shunts which can be used, especially 
on three-phase generators, when it is necessary to correct the wave shape of an 
alternator without rebuilding it. The essential features of the device are, first, 
shunts adjusted to have zero reactance for the ripples which it is desired to © 
get rid of, and, second, a limiting inductance arranged in the neutral of the 
three-phase supply, through which the shunt current produced by the ripple | 
flows. The shunt circuit consists of an air-core inductance and condensers 
arranged in series, the condensers being of fairly large capacity in order to 
reduce the voltage on them as much as possible. ‘The limiting reactance in the 
neutral may be an iron-core inductance. Curves are shown in which the method © 
has been used on four machines with bad wave shapes. A demonstration of 
the device was given at the meeting. 
19. Prof. E. W. Marcuant.—On the Currents Flowing between the 
Earth Neutral of an Alternator and the Earth Sheath of the — 
Cable System. : 
In some modern power-stations it is found that there is a considerable current — 
flowing through the earth lead from the neutral point of the alternator, even — 
when only one machine is earthed. It has been found that the current so ~ 
flowing is of three times (or a multiple of three times) the fundamental fre- 
quency. This current is due to a ripple in the pressure curve of the alternator 
between each phase and the neutral point. If such a ripple exists, a current 
corresponding with it will flow from each core of the three-phase cable network — 
to the sheath, and the currents so passing, if they are of three times (or a 
multiple of three times) the fundamental frequency, add up and do not cancel — 
each other, as do the three-phase capacity currents of fundamental frequency. — 
Oscillograms of currents observed in the earth circuits of the neutrals of — 
alternators in two large power-stations are given in the paper. n 
i a etl 
20. Mr. F. H. Ciouan, C.B.E. 
Consideration of power and speed of screws. Propelling machinery—recipro- 
cating steam engines, steam turbines, Diesel engines. Reasons for adopting 
steam turbines; need for speed-reduction mechanism. Single and double reduc- 
tion gearing. Tooth pressures, lubrication, increased stresses due to accelera- 
tion and faulty alignment i 
Electric transmission of power—alternating and direct current. Comparison 
Electric Ship Propulsion. 
