From the 18th through the late 20th century, the history of science, especially of the physical and biological sciences, was often presented as a progressive accumulation of knowledge, in which true theories replaced false beliefs. More recent historical interpretations, such as those of Thomas Kuhn, tend to portray the history of science in terms of competing paradigms or conceptual systems within a wider matrix of intellectual, cultural, economic and political trends; these interpretations, however, have met with opposition for they also portray the history of science as an incoherent system of incommensurable paradigms, not leading to any actual scientific progress but only to the illusion that it has occurred.
In its simplest form, consisting of a ring fixed in the plane of the equator, the armilla is one of the most ancient of astronomical instruments. Slightly developed, it was crossed by another ring fixed in the plane of the meridian; the first was an equinoctial, the second a solstitial armilla. Shadows were used as indices of the sun's positions, in combinations with angular divisions; when several rings or circles were combined representing the great circles of the heavens, the instrument became an armillary sphere.
Armillae are said to have been in early use in China. Eratosthenes used most probably a solstitial armilla for measuring the obliquity of the ecliptic. Hipparchus probably used an armillary sphere of four rings. Ptolemy describes his instrument in the Syntaxis (book v. chap. i.), and it is of great interest as an example of the armillary sphere passing into the spherical astrolabe. It consisted of a graduated circle inside which another could slide, carrying to small tubes diametrically opposite, the instrument being kept vertical by a plumb-line.
In this set of drawings from 1616, Galileo Galilei recorded the uneven curve of the Sun's light along the lunar surface, indicating variations in elevation. Galileo's telescope observations of the Moon and other heavenly bodies helped to convince 17th century scholars to abandon the notion of the heavens as perfect and unchanging. Before the rise of telescopic observations, the Moon was still considered by some Jesuit astronomers to be flat, with the visible spots caused by variations in density or optical phenomena. Galileo had planned a more extensive program of observations and illustrations, finding little resistance to a rough Moon, made no further lunar drawings after these.