medieval schoolmen Gilbert started his
examination of the nature of the loadstone by pointing out the
different kinds of motion due to a magnet. The five kinds (other than
up and down) are:[123]

(1) coitio (vulgo attractio, dicta) ad unitatem magneticam
incitatio.

(2) directio in polos telluris, et telluris in mundi
destinatos terminos verticitas et consistentia.

(3) variatio, a meridiano deflexio, quem motum nos depravatum
dicimus.

(4) declinatio, infra horizontem poli magnetici descensus.

(5) motus circularis, seu revolutio.

Of the five he initially listed, three are not basic ones. Variation
and declination he later explained as due to irregularities of the
surface of the earth, while direction or verticity is the ordering
motion that precedes coition.[124] This leaves only coition and
revolution as the basic motions. How these followed from "the
congregant nature of the loadstone can be seen when the effusion of
forms has been considered."

Coition (he did not take up revolution at this point) differed from
that due to other attractions. There are two and only two kinds of
bodies that can attract: electric and magnetic.[125] Gilbert refined
his position further by arguing that one does not even have magnetic
attraction[126] but instead the mutual motion to union that he called
coition.[127] In electric attraction, one has an action-passion
relation of cause and effect with an external agent and a passive
recipient; while in magnetic coition, both bodies act and are acted
upon, and both move together.[128] Instead of an agent and a patient
in coition,[129] one has "conactus." Coition, as the Latin origin of
the term denoted, is always a concerted action. [130] This can be seen
from the motions of two loadstones floating on water.[131] The mutual
motion in coition was one of the reasons for Gilbert's rejection of
the perpetual motion machine of Peregrinus.[132]

[123] _Ibid._, ch. 1, pp. 45-46.

[124] M: pp. 110, 314.

[125] M: pp. 82, 105, 170, 172, 217.

[126] M: p. 98.

[127] M: pp. 100, 112, 113, 143, 148. It need hardly be
pointed out that coitus is not an impersonal term.

[128] M: p. 110.

[129] M: p. 110.

[130] M: pp. 109, 115, 148, 149, 155, 166, 174.

[131] M: pp. 110, 155.

[132] M: pp. 166, 332. See also footnote 84.

Magnetic coition, unlike electric attraction, cannot be screened.[133]
Hence it c