Editing Edward Sabine (section)

== Magnetic crusade ==
During the decades that the Royal Navy and Royal Society devoted much energy to magnetic variation and its problems, magnetism came to be seen as an eminently "British" science.<ref name=":0">{{Cite book|last=Sabine|first=Edward|title=Contributions to Terrestrial Magnetism, Volume 1|publisher=R. and J. E. Taylor|year=1840|isbn=978-1179951232|pages=51}}</ref> There was intense interest in figuring out what many called "the great remaining physical mystery since [[Isaac Newton|Newton]]'s work on [[gravitation]]". By the beginning of the nineteenth century, it was widely recognized that the Earth's magnetic field was continually changing over time in a complicated way that interfered with compass readings. It was a mystery which some scientists believed might be associated with weather patterns.

To solve this mystery once and for all, a number of physicists recommended that a magnetic survey of the entire globe be carried out. Sabine was one of the instigators of this "Magnetic Crusade", urging the government to establish magnetic observatories throughout the empire. He also recruited many associates to the cause—most notably [[James Clark Ross]], a nephew of Sir John's, the German explorer [[Alexander von Humboldt]], the Astronomer Royal [[George Airy]] at [[Royal Observatory, Greenwich|Greenwich Observatory]] and [[Francis Ronalds]], Honorary Director of the [[Kew Observatory]].<ref name="obit_mnras"/><ref name="obit_obs"/>

A committee, of which Sabine was a prominent member, was established to work out the details. Suitable locations for the observatories were selected in both hemispheres and representations were made to dispatch an expedition to the [[Southern Ocean]] to carry out a magnetic survey of the [[Antarctic]]. In the spring of 1839, the government approved the scheme. Observatories were to be established at Toronto, [[St. Helena]], [[Cape Town]], [[Tasmania]] and at stations to be determined by the [[British East India Company|East India Company]], while other nations were invited to co-operate. Sabine was appointed to superintend the entire operation.

Most of these observatories were of limited size and were dismantled as soon as the initial survey was complete, but the one founded by Sabine at Toronto in 1840 is still in existence. Originally housed in a modest building at the newly established [[University of Toronto]], it was called the [[Toronto Magnetic and Meteorological Observatory]]. It was the first scientific institution in the country.

The birthplace of Canadian astronomy was a simple log building held together with copper nails and brass fastenings. Non-magnetic materials were used to avoid the problem of "local attraction." A second room was built to house a [[telescope]], which was used to make accurate time readings based on the movement of the Sun and stars. The modern stone observatory was erected in 1855.

In the early years, there was no way to take continuous readings: everything had to be done by hand. Thousands of painstaking observations were taken by the staff— sometimes as frequently as every five minutes. These observations were all carefully scrutinised by Sabine back in Britain. By 1846, photo-magnetographs had been developed by [[Francis Ronalds]] and Airy's associate [[Charles Brooke (surgeon)|Charles Brooke]] to [[Photography#Science and forensics|continuously record]] the magnet's movements using the recent invention of photography.<ref>{{Cite book|title=Sir Francis Ronalds: Father of the Electric Telegraph|last=Ronalds|first=B.F.|publisher=[[Imperial College Press]]|year=2016|isbn=978-1-78326-917-4|location=London}}</ref><ref>{{Cite journal|last=Ronalds|first=B.F.|date=2016|title=The Beginnings of Continuous Scientific Recording using Photography: Sir Francis Ronalds' Contribution|url=http://www.eshph.org/blog/2016/04/19/1642/|journal=[[European Society for the History of Photography]]|access-date=2 June 2016}}</ref> The new instruments were first installed at the Toronto Observatory in the later 1840s as well as at Kew and Greenwich.

In 1852, Sabine recognized from the Toronto records that magnetic variations could be divided into a regular diurnal cycle and an irregular portion. The irregularity correlated very closely with fluctuations in the number of [[sunspot]]s, whose cyclic nature had been discovered in 1844 by the German amateur astronomer [[Heinrich Schwabe]]. Sabine was the first to recognize that solar disturbances affected the Earth's magnetic environment. On 6 April 1852, he announced that the Sun's 11-year sunspot cycle was "absolutely identical" to the Earth's 11-year geomagnetic cycle.<ref>{{cite journal |last1=Sabine |first1=Edward |title=On the periodical laws discoverable in the mean effects of the larger magnetic disturbances |journal=[[Philosophical Transactions of the Royal Society of London]] |date=1852 |volume=142 |pages=103–124 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015034593494;view=1up;seq=123 |doi=10.1098/rstl.1852.0009|doi-access=free }} From p. 103: " … I have had the satisfaction of finding that the observations [of [[magnetic declination]]] of these years [i.e., 1846–1848] confirm … the existence of a ''periodical variation'', which … corresponds precisely both in period and epoch, with the variation in the frequency and magnitude of the solar spots, recently announced by M. Schwabe … "</ref>

The following year, Sabine also made a similar correlation with the Moon, establishing that that celestial body too had an influence on the Earth's magnetic field. He concluded that the Moon must have a significant magnetic field of its own to cause such an effect. But for once he was mistaken: the effect is actually the result of gravitational tides in the [[ionosphere]].

Throughout the 1840s and 1850s, Sabine continued to superintend the operation of magnetic observatories throughout the British Empire. The result was Sabine's magnum opus: as complete a magnetic survey of the globe as was then humanly possible.