- Joseph Adhemar
Infobox_Scientist
name = Joseph Adhemar
caption = Joseph Adhemar (1797-1862)
birth_date = February 1797
birth_place =Paris ,France
death_date = 1862
death_place =Paris ,France
residence =
nationality =
field =Mathematics
work_institution =
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footnotes =Joseph Alphonse Adhemar (1797 — 1862) was a French
mathematician . He was the first to suggest thatice age s were controlled by astronomical forces in his 1842 book "Revolutions of the Sea".The earth's orbit is elliptical, with the
sun at one focus; lines drawn through the summer and wintersolstice ; and the spring andautumn equinox ; intersect with the sun atright angle s. Currently, theearth is closest to the sun (perihelion ) near thenorthern hemisphere winter solstice, and the earth moves faster through its orbit when closer to the sun. Hence, the period from the northern hemisphere's autumn equinox to winter and spring is shorter by around seven days than the period from spring to summer to autumn; the reverse is true in thesouthern hemisphere . Hence, northern hemisphere winter is shorter.Because of this, Adhemar reasoned that because the southern hemisphere had more hours of darkness in winter, it must be cooling, and attributed the Antarctic
ice sheet to this. Adhemar knew of the 22,000 year cycle ofprecession of the equinoxes , and theorised that the ice ages occurred in this cycle.One immediate objection to the theory was that the total insolation during a year does not vary at all during the precessional cycle, only its seasonal distribution. Another was that the timing was wrong; however this could not be tested by the observations available at the time.
Adhemar's theory was further developed and greatly modified, first by
James Croll and later byMilutin Milankovic .Adhemar theorised about the thickness and predicted the Antarctic ice sheet (the continent had not been sighted) by comparing the depths of the Arctic and circum-Antarctic oceans. Finding the Antarctic oceans deeper (the measurements he used may not have been fully representative) and attributing this to the gravitational attraction of the Antarctic ice sheet, he postulated a truly enormous ice sheet approximately 90 km thick. Unsurprisingly, he did not convince his contemporaries.
References
* E. Bard, Greenhouse effect and ice ages: historical perspective; Comptes Rendues Geoscience, 336 (2004) 603-638 (in French and English).
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