Edward Sabine - The Magnetic Crusade

The Magnetic Crusade

During these decades the Royal Navy and Royal Society devoted so much energy to the problems of magnetic variation that magnetism came to be seen as an eminently "British" science. There was intense interest in figuring out what many called "the great remaining physical mystery since 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 disciples to the cause – most notably James Clark Ross, a nephew of Sir John's, the German explorer Alexander von Humboldt and the astronomer royal, George Airy.

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 despatch 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 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 those days, 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.

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 sunspots, 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.

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. (Nevertheless, a crater on the Moon has been named in his honour.)

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.