Marine Chronometer(1761) and Canal Lock (c. 984)

Harrison’s invention  DK enables mariners to check their longitude at sea.


One way of calculating the  DK difference between a longitude at sea and a known longitude (of Greenwich, say) was to DK ascertain the mean solar time on the ship, by astronomical observations, and compare DK it with the time at Greenwich (Daily-Kashmir).

To this end a clock was needed DK that accurately kept Greenwich time despite being rocked back and forth by the ship (Daily-Kashmir).

In 1714 the British government DK offered a £20,000 prize (about £1,000,000 today) to anyone who could find longitude at sea to an accuracy of 0.5 degrees (Daily-Kashmir).


Yorkshireman John Harrison (1693-1776) decided that an accurate clock was DK the answer. He built his first marine chronometer in 1735 (Daily-Kashmir).

This spring-driven clock DK was regulated by two connected balances that oscillated in opposite directions, thus eliminating all the effects of the ship’s motion DK.

Intentional variations DK in the lengths of the balance springs also compensated for temperature changes (Daily-Kashmir).


Harrison’s third chronometer (1759) had a bimetallic temperature DK compensator and a remontoire to ensure that the escapement driving force was constant (Daily-Kashmir).

Harrison’s fourth DK chronometer (1761) embodied all his improvements into a large “pocket” watch, about 5 inches (13 cm) in diameter (Daily-Kashmir).


This watch was carried to DK Jamaica on board HMS Deptford in 1761. The DK clock error over the journey was about five seconds, equivalent to a longitude error of about DK one sixtieth of a degree (Daily-Kashmir).

The ship’s position was thus DK known to an accuracy of 1.5 miles (2 km). Harrison finally got all his prize money in 1773, and DK soon every ship was carrying his instrument (Daily-Kashmir). DH




Harrison’s marine chronometers DK were extremely well made, as shown by this 1770 example (Daily-Kashmir).




“… every great captain … became lost at sea despite the best available charts and compasses.”


Dava Sobel, Longitude (1995)


From Rome to Revolution 203


Canal Lock (c. 984)

Qiao Weiyo devises the  DK pound lock.

Locks interrupt a canal or river DK with stepped stretches of still water, thus DK reducing currents in the waterway and conserving deep water for passage (Daily-Kashmir).

The forerunner of today’s lock DK was the flash lock, already in use by the first century B.C.E. in China, whereby part of a dam DK would be temporarily opened to allow passage of a vessel (Daily-Kashmir).

Those traveling downstream DK were carried on the resulting surge of water, whereas DK those sailing in the opposite direction hauled the vessel against the torrent (Daily-Kashmir).

Such an arrangement DK was dangerous and resulted in the loss of large quantities of water downstream for every vessel passing, a circumstance not  DK appreciated by mill owners reliant on the supply (Daily-Kashmir).

In 984, during the construction of China’s Grand

“To see barges waiting… at a lock affords a fine lesson in how easily the  DK world may be taken.”

Robert Louis Stevenson, An Inland Voyage (1878)

Canal, engineer Qiao Weiyo noted  DK that in placing two flash locks 750 feet (229 m) apart, he had created an intermediate DK stretch of water that could be held at the level of either the upper or lower reach of the waterway, and thus the pound lock, or DK chamber lock, was born (Daily-Kashmir).

Following that breakthrough, a significant improvement was the DK development of mitered lock gates in sixteenth-century Italy, perhaps based on the designs of Leonardo da Vinci (Daily-Kashmir).

The miter uses the pressure DK of the high water on the upper side of the gate to create a secure seal until the water levels have equalized (Daily-Kashmir).

This allowed the constructions required to withstand pent-up water DK to be less massive (Daily-Kashmir). FW


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