George Graham (1674-1751) was a clockmaker best known for inventing the orrery, a mechanical representation of the movement of the planets. He also designed a new form of escapement, known as the Graham or “ dead beat” escapement.
It’s interesting to note the similarity of portrait between John Harrison and his older mentor.
The going train is the main gear train – or system of gears to transmit rotational torque – in a clock. It consists of a set of wheels that connect the power source (a spring or a weight) to the escapement which drives the pendulum or balance wheel.
Spithead lies in the Solent, near Portsmouth. It is named after the Spit, a 3-mile sandbank. Always an important naval base, several island sea forts were built there in the late 19 th-century to protect Portsmouth from seaborne attack. Spitbank Fort can still be visited.
The British Fleet Sailing into Lisbon Harbour, 1736
Portugal had appealed to Britain for military assistance against mounting Spanish aggression, but Britain was determined not to become embroiled in another war. Instead, a fleet of thirty ships under Admiral Sir John Norris was sent to Lisbon in 1736 to protect British maritime trade, as well as British interests in Portuguese Brazil trade. The majority of the ships remained on uneventful guard duty near Lisbon for almost two years.
The Humber is not technically a river, as the entire body of water is tidal. The estuary forms part of the border between Yorkshire and Lincolnshire. It runs from the confluence of the River Ouse and the River Trent to the North Sea. The name Northumbria meant “North of the Humber”.
The two straight-bar balances, with a ball at each end, together make up the oscillator. Unlike a pendulum, the bar balances are independent of gravity, as the steel helical springs that connect them provide what Harrison called “artificial gravity”. Any motion affecting one balance is counteracted by the same effect on the other, so the motion of the sea had almost no effect on their period of oscillation.
Larger and more robust than the first clock, H-2 features a remontoire, a secondary source of power which is driven by the main source but which eliminates the variation of force normally inherent in weight or spring driven power.
Pierre Le Roy followed on where John Harrison left off, refining clock design with inventions such as the duplex escapement and the isochronous spiral spring. In 1769, he was awarded the prize by the Academy Francaise for discovering the best method of measuring time at sea.
A painter and cartoonist, William Hogarth intended The Analysis of Beauty (1753) as a layman’s introduction to his theory of Aesthetics. A major theme of the book is the Line of Beauty , an S-shaped line which inspired Alan Hollinghurst’s Booker Prize-winning novel of the same name.
A device to measure the angular distance between two celestial objects, the ancestor of the modern sextant was also known as the octant or reflecting quadrant. It incorporated mirrors, shades to allow observation of bright objects, a graduated scale and a removable telescope. The device was one eighth of a circle (hence “octant”) but the mirrors doubled the angle covered to a quarter circle. Crucially, the observer could see both objects being viewed at the same time (one as a reflection), reducing error. Octants were mass produced in wood and ivory.
The octant could only measure angles of 90º or less, so was eventually replaced by the sextant, which is more accurate and measures up to 120º. Sextants are still considered an important back-up to satellite and radio navigation systems.
An isolated volcanic island in the South Atlantic, St Helena is said to be Britain’s second oldest colony after Bermuda, having been taken by the East India Company in the mid-17 th century. It was an important staging post on the voyage to South Africa, and became home to the exiled Napoleon and, later, several thousand Boer prisoners of war.
The Moon’s gravitational pull deforms the shape of the oceans and even the solid mass of the Earth. The resulting tidal bulge, when offset from the Earth-Moon axis, creates torque between the Earth and the Moon. This converts the Earth’s rotational energy into heat energy, effectively braking the Earth’s rotation. Over the next one hundred million years, our 24hr day will increase in length by about one hour.
James Bradley (1693-1762) was Astronomer Royal from 1742. His discoveries include the aberration of light and the nutation (slight irregular “nodding” due to tidal forces) of the Earth’s axis. Stellar aberration refers to an effect whereby the apparent motion of a stellar body seems to vary dependent on the movement of the observer. Bradley’s observations of the apparently variable motion of the star γ Draconis formed proof of the Earth’s own movement.
Jupiter’s equatorial diameter is 143,000 km, 11 times greater than the Earth. However, Jupiter is gaseous and therefore less dense. Its volume is equivalent to 1,317 Earths, but its mass is only 318 times greater. Nevertheless, gaseous Jupiter is two and half times heavier than all the other planets in the Solar System put together.
The reflecting circle was invented by Tobias Mayer in 1752. It did not prove a great success, being so heavy it had to be used with a support attached to the belt. It was found in trials to be no more effective than the octant, and considerably less convenient.