From the late 19th century until the early 1940&#146;s, steel permanent magnets were used in applications where permanent magnets were necessary for the device to function (compasses, etc.) In the 1940&#146;s, permanent magnets improved sufficiently to be practical in applications in which electromagnets had previously been used.
(electromagnets; had been used; L:applications; T:previously) (permanent magnets; were; necessary; L:applications) (the device; to function; T:In the 1940&#146) (s, permanent magnets; improved sufficiently; to be practical in applications; T:until the early 1940&#146) Context(s , permanent magnets improved sufficiently,List([207, 249))):(steel permanent magnets; were used; L:in applications; T:From the late 19th century) (s, permanent magnets; to be; practical)
s , permanent magnets improved sufficiently,List([207, 249))
electromagnets permanent magnets the device s, permanent magnets steel permanent magnets s, permanent magnets
had been used were to function improved sufficiently were used to be
L:applications T:previously
necessary L:applications
T:In the 1940&#146
to be practical in applications T:until the early 1940&#146
L:in applications T:From the late 19th century
practical