Observing the transit of Venus on 3 June 1769 and those attending them, including Demainbray. A contemporary report by
Stephen Demainbray, the superintendent of the observatory, says: "His Majesty the King who made his observation with a
Shorts reflecting telescope, magnifying Diameters 170 Times, was the first to view the Penumbra of Venus touching the Edge of the Sun's Disk. The exact mean time (according to civil Reckoning) was attended to by Stephen Demainbray, appointed to take exact time by Shelton's Regulator, previously regulated by several astronomical observations."
Self-registering instruments Francis Ronalds invented many meteorological, magnetic and electrical instruments at Kew, which saw long-term use around the world. These included the first successful
cameras in 1845 to record the variations of parameters such as
atmospheric pressure, temperature,
humidity,
atmospheric electricity and
geomagnetism through the day and night. His photo-
barograph was used by
Robert Fitzroy from 1862 in making the UK's first official
weather forecasts at the
Meteorological Office. The network of observing stations set-up in 1867 by the Met Office to assist in understanding the weather was equipped with his cameras – some of these remained in use at Kew until the observatory's closure in 1980.
Atmospheric electricity observations Ronalds also established a sophisticated
atmospheric electricity observing system at Kew with a long copper rod protruding through the dome of the observatory and a suite of novel
electrometers and
electrographs to manually record the data. He supplied this equipment to facilities in England, Spain, France, Italy, India (
Colaba and
Trivandrum) and the
Arctic with the goal of delineating atmospheric electricity on a global scale. At Kew, two-hourly data was recorded in the Reports of the British Association between 1844 and 1847. An entirely new system, providing continuous automatic recording, was installed by
Lord Kelvin personally in the early 1860s. This device, based on Kelvin's water dropper potential equaliser with photographic recording, was known as the Kew electrograph. It provided the backbone of a long and almost continuous series of potential gradient measurements which finished in 1980. A secondary system of measurement, operating on different principles, was designed and implemented by the Nobel laureate
CTR Wilson, from which records begin in 1906 until the closure of the Observatory. These measurements, which complement those of the Kelvin electrograph, were made on fine days at 1500 GMT. Beyond their applications in atmospheric electricity, the electrograph and Wilson apparatus have been shown to be useful for reconstructing past air pollution changes.
Testing timepiece movements In the early 1850s, the facility began performing a role in assessing and rating
barometers,
thermometers,
chronometers, watches,
sextants and other scientific instruments for accuracy; this duty was transferred to the
National Physical Laboratory in 1910. An instrument which passed the tests was awarded a "Kew Certificate", a hallmark of excellence. As
marine navigation adopted the use of mechanical timepieces, their accuracy became more important. The need for precision resulted in the development of a testing regime involving various astronomical observatories. In Europe,
Neuchâtel Observatory,
Geneva Observatory,
Besançon Astronomical Observatory and Kew were examples of prominent observatories that tested timepiece movements for accuracy. The testing process lasted for many days, typically 45. Each movement was tested in five positions and two temperatures, in ten series of four or five days each. The tolerances for error were much finer than any other standard, including the modern
COSC standard. Movements that passed the stringent tests were issued a certification from the observatory called a Bulletin de Marche, signed by the directeur of the observatory. The Bulletin de Marche stated the testing criteria and the actual performance of the movement. A movement with a Bulletin de Marche from an observatory became known as an
Observatory Chronometer, and was issued a chronometer reference number by the observatory. The role of the observatories in assessing the accuracy of mechanical timepieces was instrumental in driving the mechanical watchmaking industry toward higher and higher levels of accuracy. As a result, modern high quality mechanical watch movements have an extremely high degree of accuracy. However, no mechanical movement could ultimately compare to the accuracy of a
quartz movement. Accordingly, such chronometer certification ceased in the late 1960s and early 1970s with the advent of the quartz watch movement. ==Later use==