TRANSACTIONS OF SECTION G. 777 



facturers have yet to prove the metal a satisfactory and durable substitute for 

 copper in bare overhead transmission lines, or for electrical ivork wliich involves 

 exposure to climates near the sea coast.' 



Three tables accompany the paper, the first showing the output and average 

 price of aluminium annually for the period 1890-1902 ; the second giving details 

 of the exposure tests at Waterloo ; and the third containing chemical and 

 physical tests of the aluminium wires used in the author's experiments. 



4. The Electrical Conductivity of certain Aluminium Alloys as affected hy 

 exposure to London Atmosphere. By Ernest Wilson. 



This paper gives the results of a second year's exposm-e of twenty-four alloys in 

 the form of wire '126 inch (3'2 mm.) in diameter. The first year's exposure-tests 

 were described at the Belfast meeting in 1902. It was then shown that if alu- 

 minium be alloyed with copper in varying proportions ("ll to 2'61 per cent.) the 

 effect of exposure was to increase electrical resistance to a greater extent the 

 greater tlie percentage of copper. During the second year's exposure this process 

 has progressed still further, but to a less extent. The aluminium appears to cover 

 itself with a protecting film. The manganese alloys are interesting in that they 

 have not increased electrical resistance during the second year's exposure. The 

 nickel series have also changed very little during the second year's exposure. On 

 the other hand, the nickel-copper alloys, which showed no increase of electrical 

 resistance during the first year's exposure, have changed during the second year's 

 exposure. For exposed light aluminium alloys, the results confirm the conclusion 

 arrived at in the 1902 paper, that copper alone should not be used in compara- 

 tively large quantities. 



5. A Method for finding the Efficiency of Series Motors. 

 By Ernest Wilson. 



This paper describes a method of finding the efficiency of series motors which 

 the author has found to work well in practice, and which is capable of giving 

 great accuracy. The armatures of two like machines are mechanically coupled 

 together, either through or without gearing, according as it is desired to obtain 

 the efficiency of either machine inclusive or exclusive of its gearing. In the test 

 one machine runs as a motor and delivers its energy to the other, which runs as a 

 generator, loaded on an external resistance. The two field-coils and the motor 

 armature are placed in series across the supply mains, and thus the machines are 

 conveniently magnetised to the same degree. It is usual in such tests to measure 

 the input of the motor and the output of the generator as direct quantities, the 

 difference giving the energy dissipated in the system. The losses due to electric 

 current in the respective ohmic resistances can then be subtracted from such 

 difference, and the remainder, due to eddy currents, magnetic hysteresis, brush, 

 bearing, and wind friction, can be found. Instead of measuring the volts and 

 amperes at the motor and generator terminals respectively, the author measures 

 (1) the volts at the motor terminals, and the diff'erence between these and the volts 

 at the generator terminals ; (2) the amperes delivered to the motor, and the 

 diff'erence between these and the amperes in the generator armature circuit. For 

 the latter purpose he employs two low-resistance shunts, one placed in each cir- 

 cuit, and a millivoltmeter so connected that it reads the diff'erence of potential 

 diff'erence due to the two currents in the respective low-resistance shunts. The 

 wires connecting these shunts pool the like poles of the machines together, so that 

 a voltmeter placed between their other poles reads the diff'erence of potential 

 difference of the machines. The author then gives a numerical example to show 

 that the accuracy obtainable is much greater when this difl'erential method is 

 employed, than by the first described method. 



