TRANSACTIONS OF SECTION G. 771 



any side flash which might occur shoukl any portion of the building receive a 

 direct stroke of lightning. 



The unreliability of soldered joints for conductors, whether of cable or tape, 

 has led the author to design a special joint box, which can be applied for uniting 

 any portion of the system together in such a manner as to give great mechanical 

 strength as well as good electrical contact ; at the same time any box can have 

 points inserted so as to form an aigrette in any desired position. 



Owing to the difficulty of sinking an earth plate of sufficient area, on account 

 of old foundations, a special form of tubular earth has been designed which takes 

 up little space and lias the advantage that if a suitable moist ground is not 

 obtainable the desired low electrical resistance is attained by leading a tube in 

 connection with the rain-water pipes, so that a portion of the rainfall is diverted 

 to the tubular earth. 



The author alludes to the immense amount of damage to property annually 

 occurring which might be prevented if efficient conductors were installed. He 

 mentions that instead of every church having its lightning conductor not ten 

 per cent, are so pi'ovided ; and in the case of other public buildings the percentage 

 is not much larger, the reason in the case of the former class of buildings being 

 that a vicar wishing to safeguard his church has usually to pay the cost out of 

 his own pocket. 



Architects, as a rule, treat the question of lightning conductors in a very brief 

 manner, and in their specifications seldom say anything as to the way in which 

 they are to be run, or the necessity for good joints and good earth connections. 



2. The Commercial Imimrtance of Aluminium. 

 By Professor Ernest Wilson, M.I.E.E. 



During the last ten years enormous progress has been made in the production 

 of aluminium. In 1900 no less than 5,000 tons were produced by plants having 

 25,000 horse-power, representing a capital of 2,O0O,O00L All aluminium may be 

 said to be produced by the electrolytic method, which was patented by Hall in 

 America and Herault in England and France in 1886-1887. After giving a short 

 renivie of the progress in manufacture, and a description of the electrolytic cell, 

 the author discussed the properties of the metal. From experiments made at 

 King's College, London, it appears that aluminium containing -31 per cent. Fe 

 and '14 per cent. Si has a specific resistance of 2-76 x 10~ " ohms at 15° C, which 

 shows that its conductivity is about 61 '5 per cent, that of copper, taking 

 Matthiessen's standard. In the form of wire "126 in. diameter the breaking load 

 is 12-6 tons per square inch, the limit of elasticity 8"65 tons per square inch, and 

 percentage extension within the limit of elasticity '\Q, with an applied force of 

 7'2 tons per square inch. Some copper and nickel copper alloys give 20 tons per 

 square inch, 16 tons limit of elasticity, "19 per cent, extension within the limits of 

 elasticity under an applied force of 7'2 tons per square inch, with a conductivity 

 52 per cent, of that of copper. The Standard Electric Company of California in 

 their 43 miles transmission line are stated to use aluminium having 101 tons per 

 square inch breaking load, and a conductivity 59'9 per cent, of copper. 



The weight of a given volume of a metal may govern its financial value. 

 Since copper is 3"37 times as heavy as aluminium it follows that, volume for 

 voliune, aluminium at I30Z. per ton is cheaper than copper at 70^. per ton. 



For equal conductivity the relative weights would be I of copper to |- of 

 aluminium, and the diameter of the aluminium wire would be 1 "27 time that of 

 the copper. 



Dealing with wind pressure the author stated that the total tensile strength 

 of an aluminium wire of the same conductivity as copper may be greater than 

 that of the copper, and this may compensate for increase in the surface exposed 

 to wind, snow, &c. 



A short description of some long-distance transmission lines was given, show- 

 ing that aluminium is being installed with success. It was stated that joints 



