the
invention of the thermometer and the hydrostatic balance, both of which
he devised in connection with experimentation on specific scientific
problems. Many, if not most, of the other Italian instrument inventors
of the early 17th century were his disciples. Benedetto Castelli, being
interested in the effect of rainfall on the level of a lake, constructed
a rain gauge about 1628. Santorio, well known as a pioneer in the
quantification of animal physiology, is credited with observations,
about 1626, that led to the development of the hygrometer.

Both of these contemporaries were interested in Galileo's most famous
invention, the thermoscope--forerunner of the thermometer--which he
developed about 1597 as a method of obtaining comparisons of
temperature. The utility of the instrument was immediately recognized by
physicists (not by chemists, oddly enough), and much ingenuity was
expended on its perfection over a 50-year period, in northern Europe as
well as in Italy. The conversion of this open, air-expansion thermoscope
into the modern thermometer was accomplished by the Florentine Accademia
del Cimento about 1660.

Galileo also inspired the barometer, through his speculations on the
vacuum, which, in 1643, led his disciple Torricelli to experiments
proving the limitation to nature's horror of a vacuum. Torricelli's
apparatus, unlike Galileo's thermoscope, represented the barometer in
essentially its classical form. In his earliest experiments, Torricelli
observed that the air tended to become "thicker and thinner"; as a
consequence, we find the barometer in use (with the thermometer) for
meteorological observation as early as 1649.[1]

The meetings of the Accademia terminated in 1667, but the 5-year-old
Royal Society of London had already become as fruitful a source of new
instruments, largely through the abilities of its demonstrator, Robert
Hooke, whose task it was to entertain and instruct the members with
experiments. In the course of devising these experiments Hooke became
perhaps the most prolific instrument inventor of all time. He seems to
have invented the first wind pressure gauge, as an aid to seamen, and he
improved the bathometer, hygrometer, hydrometer, and barometer, as well
as instruments not directly involved in measurement such as the vacuum
pump and sea-water sampling devices. As in Florence, these instruments
were immediately brought to bear on the observation of nature.

It does not appear,