Michael Portillo - Drawing the line

Theatre - The race to fix longitude makes an elegant, intriguing tale, writes Michael Portillo

How to measure longitude? The question haunted Britain's scientists for almost a century. The latitude of a ship at sea could be deduced by measuring the sun's angular distance from the equator. But to determine the craft's longitude was another matter. Countless lives and cargoes were lost as commanders, unaware of their position, steered their vessels on to rocks or into land masses.

King Charles II ordered an observatory to be built in 1675 at Greenwich to improve navigation and to "find out the so-much desired longitude at sea". In 1714, parliament set up a Longitude Board, composed of eminent scientists, who would award £20,000 to the person who could solve the problem of longitude.

Arnold Wesker's new play concerns John Harrison's struggle with the board, over nearly 50 years, to collect that prize money for his solution.

Harrison was a common man of uncommon engineering talent, who taught himself clockmaking. To resolve the longitude problem, he put his faith in constructing a timepiece. Provided that it was highly accurate, it could be set to the known time in a given place (for example in the port of departure) and that time could then be compared day by day with the time at the ship's position, calculated from dawn and sunset. The difference between the two times would indicate the craft's change of longitude, with each hour of difference representing 15 degrees.

The technical challenge was to construct a timekeeper that was reliable at sea. Pendulum clocks were not. Harrison worked for 19 years on sea-going clocks before abandoning that line of investigation in favour of developing a precision watch.

Wesker has brought Dava Sobel's intriguing book on this history to the stage. The disappointment with the play is that it is not, as you might anticipate, about how Harrison achieved his insights and how he progressed by stages to perfect his machine. This is the less absorbing story of his rows with the board. As the playwright views it, the Longitude Board was unbalanced in favour of astronomers, who were predisposed to think that only advances in their own field would solve the longitude problem. Indeed, some board members were competitors for the prize. They were unwilling to accept that a mechanical device - a mere clock - could provide the solution. The fact that Harrison was of humble origins and uneducated only increased their disdain.

The fault was not all on one side, however. Wesker portrays Harrison as a very stubborn character. Feeling cheated, he often behaved rudely and pig-headedly towards the board. One reason why it withheld the prize was that Harrison failed to prove that the watch could be produced in quantity. A single perfect chronometer was useless to a Royal Navy with scores of ships.

Anthony O'Donnell, as Harrison, is compelling. He exudes resentment at the unfairness of his treatment, and oozes contempt for lesser minds and social superiors alike. He is an early class warrior. Somehow O'Donnell manages to keep the audience just about on his side, despite the character's manifest personality flaws.

The play veers uncomfortably close to becoming a documentary. The disputes between Harrison and the board are often petty, and over many years the same disagreements recur somewhat monotonously. But what lifts the play well above the ordinary is Wesker's focus on Harrison as a choirmaster as well as clockmaker.

Eight of the actors are required also to sing. Their repertoire consists largely of familiar sea shanties, arranged as complex harmonies. The choir sings them unaccompanied even by a tuning fork. When the singers don 18th-century wigs and take on some of the play's speaking roles, the effect is stunning. Fiona Laird's choreography compensates for the static nature of Harrison's confrontations with the board.

From among the talented octet, I would single out Hadley Fraser, who plays Harrison's son William. As the father grew older and more cantankerous, it fell to the son to bring some tact into the dealings with the board, as well as continue work on the watch. The close relationship between Harrison and his heir is a charming feature of the piece. Giles Taylor brings hints of Obadiah Slope to his role as the piece's "villain", the Astronomer Royal, the Reverend Nevil Maskelyne.

It is, by the way, very appropriate that the play has opened in Greenwich, on the line of zero degrees of longitude and almost in the shadow of the Royal Observatory. It was Maskelyne's headquarters and now, in a neat reversal, it houses Harrison's clocks.

How to measure Longitude? It is elegantly written, the history is interesting and the singing is very fine.

Booking on 020 8858 7755 to 29 October

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