always necessary that
actualization pass from the First Cause down through each step of the
hierarchy to terminate in the qualities of the individual being. Some
of the steps could be by-passed: for instance man's body is under the
direct influence of the celestial bodies, his intellect under that of
the angels and his will under God.[20] Another example of effects
not produced through the tangible prime qualities is that of the
tide-producing influence of the moon on the waters of the ocean or the
powers of the loadstone over iron. Such causal relations, where some
members of the normal causal chain have been circumvented, are called
occult.[21]

[20] St. Thomas Aquinas, _op. cit._ (footnote 19), vol. 9,
_Summa contra gentiles_, lib. 3, cap. 92 (Quo modo dicitur
aliquis bene fortunatus et quo modo adjuvatur homo ex
superioribus causis), p. 343.

[21] St. Thomas Aquinas, op. cit. (footnote 19), vol. 17
_Opuscula, De operationibus occultis naturae ad queindam
militem ultramontem_, pp. 213-224.

While St. Thomas referred to the loadstone in a number of places as
something whose nature and occult properties are well known, it was
always as an example or as a tangential reference. One does not find
a systematic treatment of the loadstone in St. Thomas, but there are
enough references to provide a fairly explicit statement of what he
considered to be the nature of the magnet.

In one of his earliest writings, St. Thomas argued that the magnet
attracts iron because this is a necessary consequence of its
nature.[22]

Respondeo dicendum, quod omnibus rebus naturaliter insunt
quaedam principia, quibus non solum operationes proprias
efficere possunt, sed quibus etiam eas convenientes fini suo
reddant, sive sint actiones quae consequantur rem aliquam ex
natura sui generis, sive consequantur ex natura speciei, ut
magneti competit ferri deorsum ex natura sui generis, et
attrahere ferrum ex natura speciei. Sicut autem in rebus
agentibus ex necessitate naturae sunt principia actionum
ipsae formae, a quibus operationes proprie prodeunt
convenientes fini....

Due to its generic form, the loadstone is subject to natural motion
of place of up and down. However, the "virtus" of its specific form
enabled it to produce another kind of motion--it could draw iron to
itself.

Normally the "virtus" of a substance is limited to those contact
effects that could be pro