SECTIONAL TRANSACTIONS.—G. 437 
Shield have been ascertained at only afew places. The water-power already developed 
is but fifteen per cent. of the potentialities. The outstanding feature in this is likely 
to be a greatly increased development on the St. Lawrence River, where the combina- 
tion of power with deep ocean connection will be a large factor in stimulating the 
development of contiguous resources. 
Mr. H. H. Datrympie-Hay.—London Tunnelling Problems. 
In and around London there are forty-five miles of Tube railway and fifty Tube 
stations. In the construction of a large proportion of this work, for which the 
author has been responsible, tunnelling operations of varying degrees of difficulty 
have been accomplished. The paper gives illustrated descriptions of several of 
_ these, such as :— 
Cutting through a tunnel under the Thames. 
Constructing the escalators under Waterloo Station, and details of the construction 
of parts of Piccadilly Circus Station. 
The paper is prefaced by a brief general description of the construction of a Tube 
railway. 
Mr. A. L. Eaan.—WMethods of Invproving the Kata Conditions of Atmospheric 
Air in Deep-level Mines. 
The paper is a digest of the available relevant information concerning the engineer- 
ing aspects of air-conditioning in hot and humid gold mines on the Witwatersrand. 
The author indicates that the problem is bound up with the siliceous nature of the 
dust produced by mining operations and the high humidity of the atmospheric air in 
these mines, the latter factor being accentuated by the large quantities of water used 
for mitigating the evil effects of the dust. 
The paper deals mainly with the best methods for treating the ‘ hot spots’ of a 
mine. After reviewing previous work done, the author outlines further investigations 
which have more recently been carried out in connection with these questions. The 
_ law governing the power required for shaft ventilation is discussed in the light of 
tests carried out at two mines, and a description with working results is given for a 
_ dehumidification plant recently installed for experimental purposes in one of the 
mines. The position at present date is summarised, and future lines of investigation 
are suggested. 
Prof. Exisu THomson.—Pioneering in Electrical Engineering Half a 
Century Ago. 
Following the Centennial Exposition in 1876 at Philadelphia, Pennsylvania, 
U.S.A., and the Exposition at Paris in 1878, the writer’s attention was strongly drawn 
to the possibilities for new work in the field of electrical engineering—dynamo 
construction, regulation, &c. The present paper relates some of the developments 
undertaken by him in association with his colleague, Prof. E. J. Houston, work 
leading to the well-known Thomson-Houston arc lighting system, afterwards 
extensively used in the United States and later in Europe. This early work formed 
the basis of the British Thomson-Houston Company and the Compagnie-Francaise 
Thomson-Houston and similar developments in other countries. It was the combina- 
tion in 1892 of the Edison General Electric Company and the Thomson-Houston 
Electric Company which gave rise to the present world-renowned General Electric 
Company of America. 
___ The present paper first briefly describes a dynamo built by Elihu Thomson in 
1878, which may be called a pioneer structure. It was a self-exciting machine with 
commutator for continuous or direct currents, and it was also a two-phase alternator 
with collecting rings. It is notable that early in 1879 it was used at the Franklin 
Institute in Philadelphia to operate a pair of transformers connected to this A.C. 
achine in parallel by the fine wire primaries of these induction coils, later designated 
as of the ‘shell’ type, because the iron of the magnetic core was extended as a shell 
‘ 
