TRANSACTIONS OF SECTION G. 



801 



insulators, span-wire, lightning- arresters, &c. ; methods of suspension adopted on 

 British and Continental lines; feeders; double-conductor construction. 



(ff) Return Circuit. — Its importance ; supplementary return feeders ; bonds and 

 method of bonding ; electric welding. 



Notable Installations. — European and American; three-phase at Dublin, 

 Sacramento, and Portland; three-wire system; water-power; 'light railway' 

 mining, and other services. ' 



Application to Raihvay Service. — City and South London Railway ; Liverpool 

 overhead ; Chicago and New York Elevated Railways ; branch lines and suburban 

 service in connection with steam lines ; Baltimore and Ohio Railway Company's 

 95-ton locomotives. 



Conclusion. — Economic results already attained ; probable extension and 

 development. 



2. An Improved Portable Photometer.^ 

 By W. H. Preece, C.B., F.R.S., and A. P. Trotter, B.A., A.M.I.C.E. 



The authors begin by defining what is meant by illumination. When light 

 falls upon a surface that surface is said to be illuminated. The illumination 

 depends simply upon the light falling on the surface, and has nothing to do with 



the reflecting power of the surface, just as rainfall is independent of the nature of 

 the soil. It depends also on the cosine of the angle of incidence. The lio-htino- of 

 streets and of buildings may be specified by the maximum and minimum illu^mi- 

 nation. The primary purpose of an illumination photometer is to measure the 

 resulting illumination produced by any arrangements of lamps irrespective of their 

 number, their height, or their candle-power. 



The authors allude to the illumination photometers of Weber- and Mascart,^ 

 Preece's first photometer,^ the authors' modification,^ and Trotter's further modi- 

 fication,« which was used for measurements and photometrical surveys of streets 

 and public buildings in London, ] 892. The new instrument (see figure above) is 

 a box, on the upper surface of which is a diaphragm of white card painted with a 

 whitewash of magnesia and isinglass. It has one or more star-shaped perforations. 



' Published in full in the Electrician, September 20. 1895 



= Elec. Zeit. 1884, p. 166. 



* Proc.Roy. Sac. xxxv. p. 39, 1883. 



« Proc. Inst. C.E. ex. p. 105. 



1895. 



' Bull, de la Soc. Inst, des Elec. 1888, p. 103. 

 ' Proc. Inst. 3, 8, ex. p. 101. 



3f 



