Evangeli Torricelli is famous for the invention of barometer, but infact, he designed many other scientific instruments. This great scientist was born on October, 15, of 1608 in Faenza (Italy). At the age of 19, Torricelli entered the university of Rome where in later years, he became professor. His first treatise ‘A commentary on the work of Galileo’ was published in 1641. He lived during the period of famous physician Harvey and philosophers and mathematicians like Bacon, Pascal and Galileo.

At Florence in Italy, there is a museum devoted to the history of science. Among the items of exhibition, there is a telescopic lens which to the casual observer, appears to be a well developed lens a little over four inches in diameter. Even an optician will be surprised to know of the precision with which it is made. It is accurate to within a ten thousandth of a millimeter and we will be far more surprised when we learn that it was made in 1646. Its maker was Evangeli Torricelli. It was made at the time when no modern precision instruments were available. From this event we can imagine the amazing degree of accuracy which Torricelli possessed.

Most of us know Torricelli as the inventor of barometer, but only a few are aware of the interesting story behind this invention. As per this story, Grand Duke of Tuscany got a well dug in the courtyard of his palace. The surface of water was about 40 feet below the court yard level. In order to bring the water up to ground level, a hand pump was installed with its pipe dipping in the well water. The pump handle was operated repeatedly, but water did not rise in the pipe more than the height of 33 feet.

Everybody thought that there was some defect in the pump. But on careful examination the pump was found to be in quite order. This incident was reported to the Duke but he also could not understand why the pump was unable to bring water to the ground level. In these days Galileo was the mathematician to the Grand Duke. So the Duke referred this problem to Galileo. Galileo at that time was too old and practically blind. So he asked his disciple Torricelli to look into the matter.

Torricelli was aware that a heavier liquid can not be raised to the same height as a lighter liquid. He selected mercury for his experiment which is more than thirteen and a half times heavier than water. He calculated that if the measure of 33 feet is divided by 13.5, equivalent height to which mercury might rise would be about 30 inches. Therefore, the use of mercury would reduce the length of the experimental glass tube to only one yard.

To carry out the experiment, Torricelli took a glass tube of about 1 yard length with its one end closed. He filled it with mercury, closed the open end with his thumb and immersed it in a dish full of mercury so that the open end remained dipped in mercury. When he removed his thumb from the open end from below the mercury level, the mercury in the tube came down slightly and stood at a column length of about 30 inches. The upper part of the tube became empty. This empty column was named as ‘Torricelli’s vacuum. This experiment proved that water by hand pump can not be lifted to more than the height of 30 inches ´ 13.5 that is about 33 feet and apparatus used in this experiment later became the basis of evolving the barometer.

Torricelli’s barometer was taken to the peak of a mountain where the height of the mercury column was found to fall down. This proved that as we go above the surface of the earth, atmospheric pressure decreases. On the basis of the experiment pascal proved the statement of Galileo that air has weight. Today the barometer has become an essential instrument for weather men. This great Italian scientist designed several types of telescopes, microscopes and made optical instruments with an almost incredible degree of precession. He was not only an experimental scientist but also a good mathematician. He discovered the fundamental formula for integral calculus.

It was most unfortunate that this great scientist died on October 25, 1647 at the early age of 39 only. Had he lived for some more years, he would have definitely contributed a lot to the advancement of science and technology.