Although primarily known for his scientific contributions, Galileo is also responsible for progressing along several fundamental inventions that are commonplace today. He invented or contributed to the development of the telescope, the microscope, the inclined plane, the pendulum clock, the escapement, the thermoscope, the thermometer, the barometer and the ballistics site.
The invention most associated with Galileo is the telescope. He was not, however, the first to combine two lenses for magnification. The Dutch optician Johannes Lippershey invented the spyglass in late 1608. A rumour of its creation arrived in Venice in June of 1608. In the first night after hearing the rumour, Galileo had designed a telescope with threefold magnification. Thereafter, he manufactured hundreds by hand, attaining up to 32-fold magnification.
Galileo first designed the pendulum clock but never actually built one. His design was based on his observation that a swinging chandelier took as long to make an arc whether its amplitude was large or small. This is in fact inaccurate. The inaccuracy is the difference between the angle of the chandelier (or pendulum) and the sine of the angle. At small angles, the two are nearly the same. Christiaan Huygens accounted for this difference in the pendulum clock he patented in 1657. His solution was to vary the length of the pendulum through the course of the swing.
In 1641, blind and with only months left to live, Galileo designed a pendulum-based escapement. (An escapement controls the "escape" of energy from a wound spring or raised weights.) Verge escapements had been around for hundreds of years for foliot (weight-driven) clocks but were inaccurate because of the wide swing required. Robert Hooke devised the eventual solution to this problem with the anchor escapement, which fixed the swing amplitude and reduced the amplitude required.
A thermoscope is an instrument for indicating temperature change by observing an accompanying change in a substance's volume. Galileo invented a thermoscope in 1606 by warming a glass bulb with a long neck, then turning it upside down to immerse the mouth underwater. As the gas in the bulb cools, water is sucked into the neck.
The problem with this set-up is that it is affected by barometric changes, since it is not closed off.
The thermometer, i.e., a closed instrument, was developed by the 1630s by Galileo and others. Two students of Galileo invented the barometer around the same time.
Galileo received a patent for a device to raise water by horsepower. In 1595 or 1596 he created a military site that made highly elaborate projectile calculations for the day. Dutch opticians had invented the compound microscope by 1597, but Galileo developed his own. Unfortunately, such small lenses were hard to make and the microscopic world wasn't taken seriously until Robert Hooke's "Microphagia" of 1665, which inspired Leeuwenhoek's studies thereafter.