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I enjoy reading books dating from the dawn of the electrical age and I was very pleased to find, in a charity shop in Porthmadog, a copy of Chambers's Journal dated 1877. Not that this is a book on electricity, but as I scanned through the comprehensive contents pages, I spotted a few articles on recent electrical novelties. One item was entitled "Electricity as a light producer" and as I had been intending to gather a few interesting early developments to set down here, I found it most enlightening with regard to the perception of people at that time. In 1877 electricity was seen as something very interesting. Its relevance to the general public could not at that time be exactly quantified but most intellectuals knew it was going to be very important. The language of the article is very flowery in modern terms but presumably the norm for 1877. It explains the history of electricity, which, outside the laboratory, was 20-odd years old, being consequent on the invention of the dynamo. Electric light had been produced until then by aid of batteries, and the cost of their replacement, coupled with the comparatively small amount of power available from them and the low efficiency of lamps, had confined electric light to special applications. The dynamo changed that. Of course the first electric filament lamps, which awaited their discovery were poor and so initially more rewarding sources of illumination, predominantly the carbon arc was still in general use even several years after Edwardian times had drawn to a close. The "automatic" arc lamp had been invented as early as 1848 and continued in use in only slightly modified forms for 70 years. To make the arc lamp user friendly it had to be capable of being just switched on. Fiddling around with carbon rods was not a good idea (especially in the dark!) so the first practical automatic lamp used two solenoids through which passed an iron core coupled to a movable carbon rod. When voltage was applied across the carbons it was also applied to a solenoid connected across them. The solenoid coil drew the carbons apart from their rest position which was almost touching. As the spark was drawn out to a suitable length, because of a series resistance inserted in the main electrical feed, the voltage across them dropped as the arc current increased. A second coil, also connected across the carbons, drew the iron core back again. The design of the two solenoids was such that the iron core reached equilibrium at the point where the arc produced its optimum light output. This then was the design of the 1848 model and it continued with only minor changes for 70 odd years. There were other designs. Some even used small electric motors. However the arc lamp had two drawbacks. It needed a lot of power and the 65 volts required was not high enough to be compatible with the requirements of a proper universal mains supply. True, when the arc was enclosed in a vacuum it could be operated at a voltage as high as 200 and there were ways of running several arc lamps in series but it was not the complete answer to instant useful domestic lighting. Anyway, as I was saying.. the dynamo had been invented and was being brought into the lighting equation. Gas lamps were still the main way of producing light in buildings and so it was natural that one of the first applications of the dynamo was not to provide power for an electric light directly, but to provide fuel for gas lamps by breaking down water by electrolysis into hydrogen and oxygen. In 1853 a Gas Producing Company had been formed in Paris to pursue this, but unfortunately it had failed. A little later an Englishman, a Mr.Holms, had succeeded in developing a lamp for use in lighthouses based on the two gases liberated by electrolysis of water. Visitors to the lighthouse at South Foreland were surprised to see, not the usual countless barrels of oil, but two ten horsepower steam engines and a double set of dynamos. Two of everything because of course electrical machinery, being in its infancy, could not be relied upon; and if both sets of equipment failed there was also an old oil lamp ready to be pressed into service! Shortly after the invention of "limelight", as it was called, using hydrogen and oxygen, came the carbon arc. This form of lighting was very efficient but had the disadvantage of needing typically 5 kilowatts, to strike and maintain the arc. This large amount of power could only be supplied by a dynamo. The carbon arc, which as I said was the universal electric light, was very good, but in some ways too good. One arc lamp could replace 100 gas lamps and it was this very fact that made electric light a trifle unsuitable for domestic purposes. Factories and railway stations benefited from the carbon arc lamp, but although it had been developed at the outset, into a convenient, self-starting device, it still needed to be powered by a dynamo, and therefore gas lighting was the rule for the general public. |
