XL. Tests of glow-lamps, and description of the measuring instruments employed
William Edward Ayrton, E. A. Medley · The London Edinburgh and Dublin Philosophical Magazine and Journal of Science · 1895
T HE conditions under whictl the glDw-lamp can be most economical b" used have attracted considerable attention since a paper eniitled " The Most Economical Potential Difference to employ with Incandescent Lamps" was read before the Physical Society in February 1885 t by Professor Perry and one of the authors of the present communication.In this paper they stated that it was well known, from experiments made by their students in 18~0, and from results published in 1881 by Lord Kelvin, then Sir William Thomson, ~ts well as from subsequent experimeuts, that the light obtained from an incandescent lamp increased much more rapidly than the power expended in it; or, that the number of candles produced per watt of power expended in the lamp increased as the filament became hotter.But it was pointed ou~ in the paper in question that such experiments by themselves gave no idea of the commercial value of any particular glow-lamp, because they afforded no indication of its life when run at different efficiencies, and it was known that the length of time a filament would last was the less the higher its temperature.They then proceeded to show that the cest of lighting per hour per candle could be divided into two parts, viz., the cost *