One reason for the growing popularity of theatrical performances was the steadily improving quality of the technical support, and in particular the lighting. Gas lighting had been around since 1800 but provided a poor flickering glimmer that hardly lit up the actors. In 1809 Humphry Davy invented the arc lamp, which was basically just two carbon rods, each connected to one side of a battery and then brought together to make a short circuit. When the rods are taken to perhaps a millimetre apart, an intense electrical spark - an arc - flows between them and generates an immensely bright light, the same sort of brilliant white light as you get from a welding torch.

The arc lamp was by far the brightest artificial light anyone had ever seen, and arc lamps were used in lighthouses, in projectors for magic lanterns, at the Paris Opera, and later for film projectors and for street lighting. They had problems: in particular the arc evaporated tiny pieces of carbon from the rods, so that they were gradually used up and had to be continually manipulated to stay a short distance apart. This could be done with a clockwork motor, but the mechanism was tricky. Also the arc took a high current and quickly exhausted the rather primitive batteries that existed in the first half of the nineteenth century. However, they became more popular towards the end of the century, with the advent of electrical generators that could supply the power needed, and it is said that by 1884 the United States was lit up at night with 90,000 arc lamps.

In the theatre limelight provided more useful illumination. First discovered by the Cornishman Goldsworthy Gurney in 1826, limelight was sometimes called the Drummond Light, because during a survey of Ireland Thomas Drummond found that when he used limelight with a parabolic reflector he could signal 95 miles from Antrim to Ben Lomond. In the early 1820s Gurney had invented an oxygen-hydrogen blowpipe, which produced an exceedingly hot flame, and he began experimenting with various materials to see what he could do with it. He discovered that when he played this flame on to lime, especially with a little added magnesia; it produced an intense white light. Today the simplest material to use is a stick of blackboard chalk; when introduced into the oxygen-hydrogen (lame, it quickly begins to glow; and within a few seconds the light becomes dazzling - not as fierce or blinding as an arc light, but nevertheless extremely bright. As with the arc lamp, there are some problems, because the lime is gradually burned away, but limelight is much easier to handle than an arc lamp and it needs no electricity. By the 1860s limelight had become the standard for stage lighting, especially for the sun and for follow-spots - hence the phrase 'in the limelight'. Limelight was used in London theatres for fifty years, and to this day spotlights in theatres are known as 'limes'.

Alongside this developing technology there arose a new type of entertainment, based on the growing general interest in science, and in some cases theatre acts were built around scientific tricks. A splendid example of this was Pepper's Ghost, which was invented by Henry Dircks around 1858 and first demonstrated on Christmas Eve 1862 at the Royal Polytechnic in London's Regent Street by 'Professor' John Henry Pepper, a lecturer in chemistry and an enthusiastic populariser of science. Picture the scene. A dashing young man comes on to the stage and is suddenly confronted by a fearful spectre - a shimmering white ghost that appears in front of him from nowhere, floats above the floor and howls in a terrifying way. The hero, startled but brave, draws his sword and charges towards the ghost, which floats out of his way. There ensues a dramatic struggle until the hero manages to run his adversary through and through with his sword, and with a final blood-curdling shriek the ghost fades and disappears.

Here's how it worked. Below the stage a person draped in white sheets pranced about pretending to be a ghost. This ghost was out of sight of the audience but, when brilliantly lit by limelight, became visible as a reflection in a huge sheet of glass hung at an angle across the front of the stage, and it appeared to the audience to be on the stage or even floating just above it. So when the limelight was suddenly switched on, the ghost would magically appear from nowhere. During the struggle the hero was on the stage and the ghost beneath it, so they never got anywhere near one another. At the climax, when the hero 'killed' the ghost, the limelight was switched off or slowly covered over, so that the ghost slowly disappeared.

This act must have been tricky to do, since neither of the performers could see the illusion; so they must have spent a great deal of time rehearsing, with the director shouting instructions from a seat in the audience. There were technical drawbacks, too: getting the huge sheet of glass in place was a complicated operation, and the hero was inaudible behind it, so in effect the audience could hear only the ghost. However, for an audience who had not seen it before, the effect must have been astonishing; The Times described it as the most wonderful illusion ever put before the public. It certainly impressed the Prince and Princess of Wales, and the ghost was summoned to Windsor Castle. This was one of the first uses of science to create a special effect of the type that so dominates the cinema today.

On the other hand, people were fascinated by science itself and wanted to know what it was all about. The wonders of electricity and new chemistry being investigated and paraded by the famous scientists of the day brought crowds flocking to hear them lecture. Humphry Davy, the dashing Cornishman with flashing eyes and dark curly hair, and Michael Faraday, the Yorkshire blacksmith's son who never went to school but became one of the greatest scientists of his day, became seriously famous. Davy delivered such popular talks at the Royal Institution that there were tremendous traffic jams in Albemarle Street, and as a result it became the first one-way street in London.