440 SECTIONAL TRANSACTIONS.—G. 
is thought extremely well suited for all kinds of d.c. production and for wider 
purposes, too. 
In the first part of the paper the new principle is compared with the principle of 
valve commutation as known from the mercury vapour rectifier, and especially with 
the principle of sparkless commutation as developed for use in the old rotary equipment 
for d.c. production. The wearless devices upon which the spark-neglecting commuta- 
tion is based are reviewed, and results of recent investigations with regard to the 
size of the load and the voltage which can be dealt with by a simple jet-wave com- 
mutator are reported. The most striking of these results is perhaps that, while the 
largest voltage difference between two adjacent bars of the collector in a d.c. generator 
is, say, 30-50 volts, the corresponding voltage difference between the two sides of a 
jet-wave commutator, operated in hydrogen, can at least be raised to 1,800 volts 
or probably to still higher values. At the same time the load of such a commutator 
can be made as large as 100 kw.—although the jet-piece utilised in the commutator 
and forming the movable member of the same has a weight of 25 g. only. 
These extraordinary qualities of a commutator according to the principle of 
spark-neglecting commutation rendered a discussion of the various possible forms of 
spark-neglecting commutators a matter of great interest. Such a discussion has 
been carried out, and a brief review of the main results is given in the second part of 
the paper, where three new commutator types—the jet-chain commutator, the spiral 
wave commutator and the plate-jet commutator are described. All types are based 
on the wearless commutator devices developed in connection with the jet-wave 
commutator, and differ only by the way in which the moving member of the 
commutator is produced. 
In a third part of the paper the scheme of a future transmissicn of electric energy 
in the form of high-tension direct current is touched upon. The principle of spark- 
neglecting commutation permits the production of rectifiers for practically all powers 
and voltages. At the same time an inverter, i.e. an apparatus for the conversion of 
a direct voltage into an alternating voltage, can be based on the principle, since a 
spark-neglecting rectifier plant forms a reversible system. Finally, it follows that a 
step-up and step-down d.c. transformer can be built as a combination of an inverter 
and a rectifier. In a future scheme of high-tension d.c. transmission all three types 
of apparatus will be required. It was thought likely that the principle of spark- 
neglecting would lend itself better to the production of the necessary apparatus than 
perhaps any other principle of commutation. This point of view gave rise to the 
erection of a special plant for the study of the systems in question. Some results 
obtained with this plant are reported in the paper. 
Report of Committee on Electrical Units and Definitions. 
Report of Committee on Stresses 7n Overstrained Materials (see page 269). 
The following papers were presented by this Committee :— 
(1) Indentation Hardness of Test-pieces resulting from Plastie Flow.—Sir 
Henry Fow er. 
(2) The Hardness of a Steel Tube along certain ‘ Liiders’ or ‘ Probert’ Lanes. 
—Sir Henry Fow.er. 
(3) The Upper and Lower Yield Point in Steel exposed to non-uniform 
Distribution of Stress.—Prof. GILBERT Coox. 
(4) Plastic Strain in relation to Fatigue in Mild Steel—B. P. Hatten, 
D.Sc., and T. 8. Ropertson, B.Sc. 
‘ 
(5) The Phenomenon of Tensile Yield in Mild Steel and Iron—Dr. J. G. 
Docuerty and F. W. THorne. 
