Gilbert relied, in his investigations, on oft-repeated and verifiable experiments, as can be seen from his work _De Magnete_. He directs the experimenter, for example, to take a piece of loadstone of convenient size and turn it on a lathe to the form of a ball. It then may be called a _terrella_, or earthkin. Place on it a piece of iron wire. The ends of the wire move round its middle point and suddenly come to a standstill. Mark with chalk the line along which the wire lies still and sticks. Then move the wire to other spots on the _terrella_ and repeat your procedure. The lines thus marked, if produced, will form meridians, all coming together at the poles. Again, place the magnet in a wooden vessel, and then set the vessel afloat in a tub or cistern of still water. The north pole of the stone will seek approximately the direction of the south pole of the earth, etc. It was on the basis of scores of experiments of this sort, carried on from about 1582 till 1600, that Gilbert felt justified in concluding that the terrestrial globe is a magnet. This theory has since that time been abundantly confirmed by navigators. The full title of his book is _Concerning the Magnet and Magnetic Bodies, and concerning the Great Magnet the Earth: A New Natural History (Physiologia) demonstrated by many Arguments and Experiments_. It does not detract from the credit of Gilbert's result to state that his initial purpose was not to discover the nature of magnetism or electricity, but to determine the true substance of the earth, the innermost constitution of the globe. He was fully conscious of his own method and speaks with scorn of certain writers who, having made no magnetical experiments, constructed ratiocinations on the basis of mere opinions and old-womanishly dreamed the things that were not. Galileo (1564-1642) even as a child displayed something of the inventor's ingenuity, and when he was nineteen, shortly after the beginning of Gilbert's experiments, his keen perception for the phenomena of motion led to his making a discovery of great scientific moment. He observed a lamp swinging by a long chain in the cathedral of his native city of Pisa, and noticed that, no matter how much the range of the oscillations might vary, their times were constant. He verified his first impressions by counting his pulse, the only available timepiece. Later he invented simple pendulum devices for timing the pulse of patients, and even made some advances in applying his discovery in the construction of pendulum clocks. b +---------+ | | | | | | +---------+ | | +---------+ | c | | | | | | | d | | | | e