Sir William Watson, FRS was a physician, botanist and scientist. Born to a respectable tradesman on 3rd April 1715 in Clerkenwell, he entered the Merchant Taylor School in 1726 and was apprenticed to an apothecary in 1730. In 1738, he married and set up business on his own account.
He was elected to the Royal Society in 1741, although it would appear that he had not submitted any papers before then. From that time, until his death, he delivered 58 original papers and summaries of others’ on medicine, botany and electricity. His electrical experiments drew the attention of the great and the good. Even the Prince of Wales (future George III) visited his home to watch and the Duke of Cumberland was rewarded with a shock from the tip of his sword that had recently seen action at Culloden. Watson became a physician in 1759 and the Bugle Lily, ‘Watsonia’ bears his name. He was known for his clear, energetic speech, keen observations, extraordinary memory and, as a medical doctor, his humanity.
In 1747, he and a number of other gentlemen of the Royal Society conducted experiments to determine the velocity of electricity and whether it was faster than sound. It was at this time that he coined the term “circuit”. They conducted a series of experiments in wet and dry conditions across the Thames at Westminster, the New River and fields in Stoke Newington and dry fields in Highbury, over a variety of distances up to one mile. Even at this distance, the velocity appeared instantaneous, and they cast about for a location that would be suitable to conduct the experiment in dry conditions over twice the distance.
“…it was neceffary, that the Houfe, wherein the electrifying Machine was placed, fhould be vifible at leaft at one of the Stations; and that the Space between that Houfe and the Stations, through which the Wire was conducted, would be very little interacted by Hedges, Roads, or Foot-paths ; neither fhould the Wire in this Space be fubject to be difturbed by the Horfes or Cattle, which were grazing – y nor ought it to touch in its Paffage the Trees or any other Vegetables, which at this Seafon of the Year were every-where luxuriant. To find a Place within a convenient Diftance of London with thefe Requisites was not very eafy; but at laft, Shooters Hill was pitched upon, as the moft convenient.”
On 14th August 1747, at Shooters Hill, William Watson met Prof. Bradley, Peter Daval Esq, Mr George Graham, Richard Graham Esq, Mr Nourse, George Lewis Scott Esq, Mr Short, Charles Stanhope Esq, all of the Royal Society and Dr Bevis.
Three observers were placed at the seven mile stone (Mr George Graham, Mr Short and Charles Stanhope Esq, with another observing Mr Graham to note the time lapse, referred to below) and others at the nine mile stone, each standing on wax and each holding an iron rod which rested on the ground.
A Leyden Jar (an early form of battery) was placed upstairs in a house on the western side of the hill and connected via wires, wound round a series of dry sticks, to each of the observers. The distance from the house to the seven mile stone was 6,732 feet. Unfortunately, the sticks could not be fixed securely in the strong gravel, which had no cover of soil. In some places the wire touched brambles and other bushes and, in one field, the ripe barley. The distance from the house to the observer standing in a corn field close to the nine mile stone was only 3,808 feet, so the observer was placed at sufficient distance beyond the milestone that the two observers stood 2 miles and 40 feet apart, via the Leyden Jar in the house. The posts this time were well-secured in clay and the wires did not touch any bushes. The group had determined to discharge the Leyden Jar 12 times. A man would fire a musket outside the house, whilst the one within would simultaneously discharge the jar. The observer would then note the time lapse between observing the effects of the electricity and hearing the report of the gun.
After eight explosions, however, nothing had been felt by the observer near the seven mile stone, whereupon it was discovered that the wire had been broken and poles knocked down by a man who had ridden straight through them. The wire was fixed and another twelve explosions were made “without further molestation.”
All of the first eight discharges and eleven of the following twelve caused a strong shock in the observer near the nine mile stone. At the twelfth, he decided to stand on the wax without allowing his iron rod or any part of his body to touch the ground. This time he felt only a slight tingling in the thumb and finger holding the wire.
The group then encouraged two “country fellows”, who had been watching with interest, to join in. The first held the wire in one hand and then, along with his friend and four of the experimenters, formed a chain, standing directly on the ground and not utilising the iron rod.
“Upon the Explofion they were all fo ftrongly fhocked in their Arms and Ankles, that the Countrymen could by no means be prevailed upon to try the Experiment again.”
Although the gentlemen near the seven mile stone had been oblivious to the first eight discharges, they felt all of the latter twelve. This confirmed that a circuit of 4 miles had been created; viz, two miles of wire and two miles of ground! How much further “electrical commotion” might be felt they could only speculate. The sensation at the seven mile stone was much less than that felt beyond the nine mile stone, as so much of the wire had touched moist vegetation and thereby created sub-circuits.
The time it had taken for electricity to travel from the house to Mr George Graham had been so fast as to have been virtually instantaneous. However, the experimenters were not happy with this conclusion and wanted to ascertain the absolute velocity of electricity over a certain distance, if possible.
To this end, on 5th August the following year, Mr William Watson met at Shooters Hill the President of the Royal Society, Rev Birch, Rev Mr Professor Bradley, James Burrow Esq, Mr Ellicott, Mr George Graham, Richard Graham Esq, the Rev Mr Lawrie and Charles Stanhope Esq.
This time an observer was to hold in each hand a wire, a mile long, connected to a Leyden Jar at the house, within view of the window so that he could observe the explosion. Another observer was to note the lapse in time between the explosion at the window and the convulsive motions in the arms of the observer forming part of the circuit.
Unfortunately, the distance put them at the side of the road. They knew enough now, that they must just avoid allowing the wires to touch the ground, each other or any other conductor, so such a great distance was not necessary. Instead, they positioned themselves in a field just fifty yards from and within view of the window, then ran the wires up and down the length of said field, held aloft on dry wooden sticks. As it had rained the night before, great care was taken that the wires did not touch the damp wood around the window.
The jar was discharged several times and each time the observer’s arms convulsed simultaneously. Several variations were tried: more than one observer held hands; the observer stood close to the jar; the two ends of the wire touched – but no difference in the time lapse was observable. As had been noted in the experiments the year before, an observation was made linking the length of the circuit and the strength of the explosion in the jar: the longer the circuit, the less forceful the explosion. At this time they did not understand resistance and did not enquire further.
Thus ended the shocking experiments on Shooters Hill, which were presented to the Royal Society on 29th October 1748. Having concluded that electricity was some kind of fluid, Watson decided not to pursue his electrical experiments a few years later, choosing to concentrate in his medical career instead. He did continue to take an interest, however, and supported others in presenting evidence to the Royal Society. He became a champion of Benjamin Franklin. William Watson was knighted in 1786, just a year before his death on 10th May 1787.