Archaic spelling of en“equilibrium” in the Oxford English Dictionary (second edition), giving æquilibrium as a 17th–19th-century spelling.
1734, John Keill, Maupertuis, An Examination of Dr. Burnet’s Theory of the Earth, page 93:Now in a ?pherical fluid, all who?e parts gravitate towards the Centre, I think it is evident from the principles of Hydro?taticks and fluidity, that all tho?e Bodies which are equally di?tant from the Centre, mu?t be equally pre?t with the weight of the incumbent fluid, and if one part come to be more pre??ed than another, that which is mo?t pre??ed will thru?t that out of its place which is lea?t, till all the parts come to an æquilibrium one with another, and this is known by a common and ea?y experiment, if you take a recurved tube as in the figure, 4. Plate II. and fill it with water or any other fluid, it will ri?e equally in both Legs of the Tube, ?o that the ?urfaces C E and F I are equally pre??ed by the weight of the incumbent columns B C E D, G F I H, but if one of the Legs of this Tube ?hould be filled with oil, or ?ome other lighter fluid, and the other with water, the lighter fluid will ri?e higher than the other, for otherways, the?e ?urfaces which are equally di?tant from the Centre could not be equally pre??ed.
