Editing Magnetometer (section)

===Early magnetometers===
[[File:Stanley compass 1.jpg|thumb|right|The compass is a simple type of magnetometer.]]

[[File:Coast and Geodetic Survey Magnetometer Plate XV Fig 1 WBClark 1897.jpg|thumb|right|Coast and Geodetic Survey Magnetometer No. 18]]

The [[compass]], consisting of a magnetized needle whose orientation changes in response to the ambient magnetic field, is a simple type of magnetometer, one that measures the direction of the field. The oscillation frequency of a magnetized needle is proportional to the square-root of the strength of the ambient magnetic field; so, for example, the oscillation frequency of the needle of a horizontally situated compass is proportional to the square-root of the horizontal intensity of the ambient field.{{citation needed|date=October 2020}}

In 1823 William Scoresby (1789-1857), an English explorer, scientist and clergyman, was deeply involved in magnetic science, particularly in improving ships' compasses.  In 1823, he published a paper in the ''Transactions of the Royal Society of Edinburgh'' titled "Description of Magnetimenter, being a new instrument for measuring magnetic attractions and finding the dip of the needle; with an accont of experiments made with it." 

In 1833, [[Carl Friedrich Gauss]], head of the Geomagnetic Observatory in Göttingen, published a paper on measurement of the Earth's magnetic field.<ref>{{cite web |author=Gauss, C.F. |date=1832 |title=The Intensity of the Earth's Magnetic Force Reduced to Absolute Measurement |url=http://21stcenturysciencetech.com/translations/gaussMagnetic.pdf |access-date=2009-10-21}}</ref> It described a new instrument that consisted of a permanent bar magnet suspended horizontally from a [[gold]] fibre. The difference in the oscillations when the bar was magnetised and when it was demagnetised allowed Gauss to calculate an absolute value for the strength of the Earth's magnetic field.<ref>{{cite web |url=http://www.ctsystems.eu/gauss.htm |archive-url=https://web.archive.org/web/20070930141937/http://www.ctsystems.eu/gauss.htm |archive-date=2007-09-30 |title=Magnetometer: The History |publisher=CT Systems |access-date=2009-10-21}}</ref>

The [[gauss (unit)|gauss]], the [[CGS]] unit of [[magnetic flux density]] was named in his honour, defined as one [[maxwell (unit)|maxwell]] per square centimeter; it equals 1×10<sup>−4</sup> [[tesla (unit)|tesla]] (the [[SI unit]]).<ref>{{cite web|title=Ferromagnetic Materials|url=http://phareselectronics.com/ferromagnetic-materials/|access-date=26 May 2015|archive-url=https://web.archive.org/web/20150627075722/http://phareselectronics.com/ferromagnetic-materials/|archive-date=27 June 2015|url-status=dead}}</ref>

[[Francis Ronalds]] and [[Charles Brooke (surgeon)|Charles Brooke]] independently invented magnetographs in 1846 that continuously recorded the magnet's movements using [[photography#Science and forensics|photography]], thus easing the load on observers.<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> They were quickly utilised by [[Edward Sabine#The magnetic crusade|Edward Sabine]] and others in a global magnetic survey and updated machines were in use well into the 20th century.<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 book|title=Encyclopedia of Geomagnetism and Paleomagnetism|editor1=David Gubbins|editor2=Emilio Herrero-Bervera|publisher=Springer|year=2007|isbn=978-1-4020-3992-8}}</ref>