54
ESSEX WORTHIES.
down from Plutarch and Ptolemy that garlic rubbed over a magnet
destroys its power, unless, according to Ruelius, it be restored by
anointing it with goat's blood. Another fable of Marbodeus, that a
magnet is powerless in the presence of a diamond, is also refuted by
Porta. The latest work on magnetism, prior to the appearance of
Gilbert's treatise, was a small pamphlet which appeared in 1597,
entitled "The Seaman's Supply," by William Barlowe, which gave for
the use of navigators many facts about the declination of the com-
pass at different sea-ports, and about the amount of the dip at
different parts of the earth.
All these earlier publications in magnetic subjects consisted, as
will be noticed in the announcement of isolated facts and properties
rather than in any systematic investigation or consistent explanation.
The significance of the facts was not seen ; and they were in many
cases mixed up with exaggeration and myth. The only explanations
or hypotheses which had been advanced as to the cause of the ten-
dency of the magnet or magnetised needle to point geographically
north and south were wild in the extreme. Gilbert himself enumer-
ates sundry of them in order to show how empty and ridiculous they
were. Serapio Mauritanus and others reported that in the Indies
there were magnetic mountains which would attract the ships as they
sail by and pull the iron nails out of them. Paracelsus and Cardan
considered that the magnet was governed by some virtue proceeding
from the constellation of the Great Bear ; and after the discovery that
the magnet did not point truly northward, Cardan suggested that the
star in the tip of the tail of the Great Bear was itself a magnet.
Bessard declared that the compass pointed not toward the pole of the
earth, but to the pole of the zodiac. Olaus Magnus and after him
Maurolycus declared that there was a magnetic island or loadstone
rock in the north sea toward which the compass turned its point.
Plancius even showed its position upon a chart of the globe.
Such was the state of the science when "De Magnete" appeared.
The full title of the book, as it appears on the frontispiece of the
folio edition of 1600 is: Guilielmi Gilberti Colcestrensis, media
Londinensis, de magnete, magneticisque corporibus, et de magno magnete
tellure; Physiologia nova, plurimis et argumentis, et experimentis
demonstrata. Londini. Excudebat Petrus Short. Anno M.D.C.
The volume opens with a glossary of terms and a table of con-
tents. The work is divided into six books, each book being sub-
divided into numerous short chapters.