It's easy to assume (or so I'd always assumed) that the adoption of new technologies is largely down to some assessment of the inherent qualities of the proposed innovations, so I always find it intriguing to come across instances where other factors are at work. I came across one example in writing a paper I gave about
Tobias Mayer a few months ago.
It centres around the trials and adaptation of a circular instrument (a repeating circle) designed by Mayer and of which he sent a wooden model to London in 1755. The circularity of the instrument was crucial to Mayer's claims that it could be used for accurate observations of
lunar distances at sea, since by making repeated observations around the circle and then averaging them, you are taking advantage of the fact that a circle is always 360 degrees, so that even if you haven't divided its scale evenly the differences cancel out. The circle by its nature guarantees the instrument’s accuracy.
But this principle was abandoned when the prototype came to Britain, where a brass version was made by one of London's most trusted instrument makers, John Bird. Sea trials by
Captain John Campbell showed the new instrument to be cumbersome, however, with only a third of the scale usable. The solution,
James Bradley, the Astronomer Royal, later wrote, was that,
as the principal use of this [circular] construction is to obviate the inconvenience proceeding from the inaccurate division of instruments and as that might be sufficiently removed by the care and exactness with which Mr. Bird is known to execute those that he undertakes to make; a sextant of a radius, twice as long as that of the circular instrument, was made by him, and afterwards used by Capt. Campbell in taking several observations on board the Royal George in different cruises near Ushant in 1758 and 1759
This translation from circle to
sextant meant discarding the mathematical certainty of the circle for the contingent guarantee of accuracy provided by the craftsmanship of one man, John Bird. To Bradley, Bird was so good that his name on the instrument was guarantee enough.
In later years Bird received a reward from the Board of Longitude for publishing an account of his method of dividing arcs by hand. Valuable hands indeed.
Images
Portrait of John Bird (National Maritime Museum, Greenwich, neg. PW3435)
Bird's signature on an early marine sextant, c.1758 (National Maritime Museum, Greenwich, museum no. NAV1177)
