SECTIONAL TRANSACTIONS.—G. 439 
In addition to gas, the industry produces smokeless fuel—coke. Lately much 
attention has been given to the scientific production of this fuel, and special apparatus 
evolved for its use. 
The production and distribution of fuels, however desirable, must be accompanied 
by a selling organisation giving expert advice, demonstrations and maintenance 
facilities ; the new gas industry has developed such services. 
The increasing demand for gas and coke finds parallels in the experiences of other 
highly-organised countries. In America the sale of gas is seven-and-a-half times 
that in this country, and has increased 110 per cent. in ten years. Similar results 
are noted in Germany, Sweden and Switzerland. 
In Germany much interest has been aroused in the Ruhr Gas Grid, extending to 
1,800 miles of main and designed to dispose of 300,000 million cubic feet of gas from 
the coke ovens. Parliament has recently passed such a scheme for the neighbourhood 
of Sheffield, following upon the recommendation of a Government committee to 
consider a gas grid in the north of England. 
The gas industry endeavours to treat its employees as thoroughly as its consumers, 
and mention is made of copartnership schemes and welfare work. 
The situation concerning low-temperature carbonisation, in the light of smokeless 
fuel and home-produced oils, is reviewed. The suggestion is made that various 
hydrogenation processes may render oils from high-temperature carbonisation suitable 
‘substitutes for imported oils, and that coal blending and pre-treatment can result 
in improved smokeless solid fuels. 
It is claimed that the gas industry of to-day is virile, scientific and progressive. 
Prof. E. G. Coxer, F.R.S.—Force Pits and Shrinkage Fits. 
A number of important cases arise in engineering practice, in which two parts 
of a machine or structure are connected together by forcing one part into a hollow 
of slightly less size in the other part, or alternatively cooling the first part in liquid 
air or other refrigerant, so that when it is set in position it is, temporarily, slightly 
smaller than the hollow, but ultimately regains its original size, and then exerts 
considerable pressure on the part in which it is placed. 
Other familiar cases are the heating of enveloping bodies, such as tyres for wheels 
and straps for crank webs, so that the envelope can be readily placed in position, and 
then shrunk by cooling to give a firm grip of the interior member. In such cases of 
engineering practice the stress distributions produced in the assembled parts are 
usually difficult, if not impossible to solve by analysis. 
Experimental measurements have been made of the strains experienced in wheels 
and other bodies, from which the stress distributions were inferred. 
The present paper deals with experimental observations on crank webs, locomotive 
wheels, boiler tube plates and the like, in which the processes mentioned above are 
carried out with transparent models, and the stress distributions are measured by 
photo-elastic means. 
A number of such cases are described in some detail, and the applications to actual 
practice of the measured stress distributions are discussed in connection with the 
theory of stress distributions in multiply connected plates. 
Prof. C. F. Jenkin, C.B.E., F.R.S.—Harth Pressure Investigations. 
Report of Committee on Earth Pressures. 
Wednesday, September 30. 
‘Prof. Jutius Harrmann.—Spark-neglecting Commutation: a New 
Principle in Large Power D.C. Production. 
At the Leeds Meeting in 1927 a new mechanical rectifier for large powers, the 
‘el-wave rectifier, was described to the members of SectionG. This rectifier introduced 
a new principle, the principle of spark-neglecting commutation, into practical electro- 
_ technics. The present paper is a plea for the adoption of this principle, which 
