The name Daniel McFarlan Moore may not be familiar to many people, a shortcoming I shall try to redress. He was a distinguished American electrical engineer and inventor who died in 1936; the circumstances were very unfortunate because he was shot dead at his home in New Jersey by an out of work rival inventor. It appears the rival had expected commercial success from some new development and was annoyed to discover Moore had already patented it. The murderer, Jean Philip Gebhardt, later committed suicide.
Moore is probably best known for his 1917 invention of the later-ubiquitous neon indicator lamp. Although, now, less common than they used to be, neon indicators were once to be found in nearly all household and commercial electrical equipment to indicate presence of a high voltage, such as connection to a mains power supply. They had the advantage of glowing quite brightly while generating minimal heat and having a very long life. The invention was not specific to the one gas and although neon (which glowed orange/red) was perhaps the most common, variants using other gases glowed a different colour, such as argon which glowed blue. The lamps usually comprised two electrodes in a small glass capsule and the presence of a high voltage between the two caused a coronal (light emitting) discharge around the negative electrode; alternating current produced a discharge around both electrodes during the corresponding negative cycles. The same effect was produced in other later applications of the invention, such as the ‘nixie’ tube where a glass bulb (like an old radio valve) contained a wire cage which formed a single positive electrode within which were ten negative electrodes comprising thin wire shapes in the form of the numbers 0-9, stacked one behind the other. When a negative charge was applied to any one of these shapes the corresponding figure would illuminate brightly, enabling the tubes to be used as numerical read out devices. If you would like to see a lot of different types of counting tube that were developed from the humble neon indicator, you can do so by clicking HERE.
Prior to the invention of the neon lamp, Moore had been experimenting with the production of light by means of a gas discharge through a glass tube. The object was to produce a high quality light that could provide even illumination at low cost. He was able to demonstrate the possibilities as early as 1894, but it was not until 1904 that a commercially viable solution was achieved. It is necessary to recall that his research started at a time before the tungsten filament lamp had become a practical means of illumination (from 1911) and until then the choice was between arc lamps and early incandescent lamps that were fragile, not very bright and not entirely reliable. The arc lamp suffered from the disadvantage (among several) that it gave out an extremely intensive light that was too bright when close; they were quite unsuited to use in relatively small spaces and their point sources created deep shadows. Moore attempted to produce a lamp that created adequate light evenly over a large area, without shadow and with high reliability. Moore had previously worked with Edison and did not think much of Edison’s incandescent lamps, telling the great inventor they were too small, too hot and too red, before departing and setting himself upon the task of making an efficient lighting system.
The Moore lighting system consisting of a single, continuous glass tube of at least 1¾ inches in diameter that was sealed at both ends. The tube was typically between 200 and 300 feet long and was filled by a suitable gas at low pressure (a thousandth of an atmosphere is indicated in scientific paper describing the arrangement). At the ends of the tube, carbon electrodes were arranged and a very high voltage was applied between the electrodes, a minimum of 5000 volts being required. Some of the later reports describe the use of a 3-phase supply (to avoid the discernible flicker that a single phase produced) but I have as yet been unable to establish how such a supply would be wired up or below what frequency it was desirable. The high voltage caused the low-pressure gas to become excited and the excess energy was released as light, causing the gas inside the tube to glow. If air were used the gas glowed a rosy red, if pure nitrogen were used the colour was pinkish-red and if filled with carbon dioxide it glowed white (almost equivalent to daylight). The efficiency of Moore’s lighting was reckoned at about 70 per cent, depending on how it was measured. Edison’s throw-away incandescent lamps were lucky to achieve two or three per cent.
Unfortunately, it was found in practice that the ongoing electrical discharge slightly increased the intensity of vacuum in the tube, tending to reduce lamp efficiency. To counter this, an ingenious form of regulator was devised which measured the circuit resistance; if this altered as a result of unduly low pressure the regulator allowed a minute quantity of gas to enter via a porous plug to correct the deficiency. If the tube was filled with air, this was straightforward, but if with pure nitrogen or carbon dioxide a certain amount of chemical apparatus was required to create a small reserve of the preferred gas.
During the period when the Central London Railway was being extended to Liverpool Street (opened in 1912) the company sought to provide better lighting than on its original system, and particularly sought to avoid arc lights, which the company was trying to remove. A challenging problem arose along the three inclined escalator and stair shafts in the connection with the Great Eastern Railway, the station being provided with escalators from the beginning and the company not having had to contend with lighting an inclined shaft previously. Discussion with Moore suggested installation of one of his tubular lights would fit the bill. The resulting tube was 274ft 8ins long, and as we know each shaft was about 90ft length, this suggests a single tube would wend its way along all three shafts in one continuous length (such a labyrinthine arrangement of Moore’s tubes was not unusual). The main practical problem was the welding together and bending of the various short tubes to make a continuous tube, requiring glass-welding skills. The electro-motive force required across the electrodes for this particular installation was about 17,500 volts, created by a transformer. The output was stated to be 55 candle-power per yard and at 1.3 to 1.7 watts per candle this would rate the equipment at roughly 82 watts per yard, or a little over 7.4 kW for the entire installation, probably a little more than would have been the case with incandescent lamps.
It may be seen that the design was complicated by the need to include the regulator mechanism and in later installations it was found possible to fix the electrodes to the outside of the glass and this made the internal pressure stable, avoid the need for the complicated regulator altogether. Even so, the advances being made with cheap and easy-to-install incandescent lamps reduced the commercial attractiveness of Moore lighting except for specialist installations, which is why few people have heard of him. Moreover, Moore lighting did not have an indefinite life and was difficult and expensive to replace.
Contemporary lighting magazines stress that one of Moore’s objectives was to produce a lighting system that contributed to the architectural effect as well as providing high quality light. It appears its main customer had been department stores around New York and we know the first installation was in 1904 at a hardware store in Newark (New Jersey). The largest installation was in the US post office in New York, involving seven 200ft tubes. In England, before the Liverpool Street installation, there had been another in London in the forecourt of the Savoy hotel, installed within the glass porch in 1907. This installation involved a nitrogen-filled tube of 176ft total length and the soft light it produced introduced no shadows and no glare. A problem arose as the local electricity supply was direct current and a small motor generator had to be installed to produce the alternating current required. A further installation at about the same time was made at Salisbury House involving an 85ft tube filled with carbon dioxide. However, it is doubtful that any new installations of ordinary lighting were made after the Great War as other technologies were now found more suitable.
Moore’s efforts were by no means in vain. In 1912 he sold his patents to General Electric and they later became a component in the work done in developing the fluorescent tube during the 1930s. This differed from the Moore tube in introducing mercury in addition to the ionizing gas such that the emitted light was in the invisible ultra-violet region and used to excite a phosphor on the inside of the tube; it was the glowing phosphor that created the light output. London Transport tested fluorescent tubes in 1944 at Piccadilly Circus and it is fitting that they were first used on a large scale on the 1946-49 Central Line extensions that began at Liverpool Street.
I have not yet found when the Moore installation at Liverpool Street was removed, and would be interested if more information comes to light.