Adrien Auzout's parents were Adrien Auzout and Jeanne Piedelièvre. Adrien and Jeanne were married in 1618 and they had seven children. Adrien, the subject of this biography, was the eldest of the children, having three younger brothers and three younger sisters. Adrien Auzout Senior was an administrator in the Rouen law courts. He preserved the court records but was not himself a lawyer. This was not a particularly well paid job and, having a large family, it was hard for them to make ends meet. Adrien, the subject of this biography, grew up in Rouen in a difficult period; the government had imposed very high taxes to pay for the Thirty Years War and epidemics of the bubonic plague swept the area in the 1620s and 1630s.
Adrien Auzout was fortunate to be the eldest of the children, for the family finances would not have stretched to educating the younger children. He was able to study at the Jesuit College in Rouen and, although there is no record of Auzout knowing Blaise Pascal around 1640, both must have attended the Rouen Jesuit College at this time, so probably did know each other. Some sources claim that Auzout and Pascal collaborated after Pascal settled in Rouen in 1639. What is undoubtedly true is that both became interested in the vacuum around 1646 whether working together of individually. Certainly Auzout was present when Pascal gave public demonstrations in Rouen of variations on Torricelli's experiments inverting a column of mercury in a tube and observing the space above it which he correctly claimed must be a vacuum. Pascal not only carried out the experiment with tubes containing mercury but also with much longer tubes containing water and wine.
Auzout's father expected his eldest son to follow the family tradition, which certainly stretched back at least two generations, and become an administrator in the law courts. It was not to be for Auzout had other ideas about his future. In 1647 he left Rouen and settled in Paris, some sources claiming that he went with Pascal in the spring of that year. There he joined Mersenne's circle, sometimes called the Montmor Academy, where he deepened his knowledge of mathematics and physics interacting with the other leading scientists of the day who were part of the group. He told Gassendi of the experiments he had seen Pascal carry out. In the autumn of 1647 Auzout :-
... designed an ingenious experiment - creating one vacuum inside another - in order to prove that the weight of a column of air pressing on a barometer causes the mercury to rise inside.
He designed the apparatus in which a mercury barometer was inside a vacuum created by inverting a tube of mercury. The mercury in the barometer completely descended into the vessel below showing that air pressure caused it to rise.
When his father died in 1652, Auzout inherited some money but, given the financial state of the family, it would not have been a lot. Sturdy investigates in  where his income came from; it was sufficient apparently let him live fairly comfortably in Paris:-
He also practised astrology, augmenting his income by casting horoscopes for prominent Parisian nobilities; and by 1666 he was receiving gratifications of 1500 livres a year from the crown. By these and perhaps other means Auzout evidently made enough money to survive in Paris, even if he was not necessarily a wealthy man. Little is known of his marriage. His wife would have brought a dowry, but almost certainly kept most of it for her personal rather than their joint use. Their relationship was far from happy, and when he departed from France in 1668 he left her behind.
We do have a couple of pieces of information concerning people for whom Auzout undertook work. We know that in the summer of 1648 he left Paris to undertake work for Jacques de Crevant de Brigueil, the abbée de Saint-Maixent in Poitou. Later he worked for Alexandre d'Elbène; he administed some of d'Elbène's estates and received a substantial sum in 1662 for his efforts to increase the estate's revenue.
Auzout's interest in mathematics led to him arguing that a treatise on the quadrature of the circle was in error. He wrote a treatise on proportion and produced a method to construct an ellipse which he sent to Frans van Schooten. By 1660 Auzout had become totally absorbed by his interest in astronomical instruments. He wrote to King Louis XIV in 1664 indicating that there was a need for a public observatory, and that the Compagnie des Sciences et des Arts was ready to begin work on the project if it received Royal sponsorship. This is of interest since the Observatory was established in 1667 as a result of the petition, and also since it suggests that Auzout was leading a group from Mersenne's circle who were seeking a formal status. The Compagnie was a bridge between Mersenne's circle, called the Montmor Academy, and the Académie Royale des Sciences founded in 1666.
Auzout produced a pamphlet concerning the orbit of the first of two comets of 1665, predicting an orbit for the comet based on about five observations he had made. The Royal Society in London decided to try to verify or disprove Auzout's predicted orbit by looking at observations of the comet made by others. Observations by Johannes Hevelius had led him to disagree with Auzout's predictions and a controversy between the two arose, particularly over one observation of the comet by Hevelius on 18 February 1665. The Royal Society resolved the dispute in favour of Auzout, declaring :-
... that whatever Hevelius had seen on the night of 18 February near the first star of Aries, it had not been the comet.
The importance of Auzout's work on comets is his belief that they followed regular orbits and were thus permanent members of the solar system. He also hoped that the distance to the comet and its magnitude could be calculated, and so a proof given that the Earth is in motion.
Working mainly with Jean Picard, Auzout worked on instruments to improve telescopes and surveying instruments :-
He made a significant contribution to the final development of the micrometer and to the replacement of open sights by telescopic sights. ... By the summer of 1666 Auzout and Picard were making systematic observations with fully developed micrometers.
In a letter sent on 28 December 1666 to Henry Oldenburg, the first secretary of the Royal Society of London, Auzout explained how his new micrometer, with two parallel wires either of silk of silver, one of which could be moved by a screw, could be used to calculate the diameters of the planets and the parallax of the moon. He also considered the question of why, in the last eclipse of the sun, the diameter of the moon appeared larger towards the end of the eclipse that at the beginning. Auzout was not the first to invent a micrometer but it is his design which has become the basis of the modern instrument. Wolf explains further in :-
The turns and fractions of a turn of a micrometer screw could be converted into angular measurements after the instrument had been calibrated... The pendulum clock, used in this calibration, found its principal application in enabling the times at which selected stars crossed the meridian to be accurately noted. The interval between the transits of two stars measures their difference of right ascension; and upon Picard's procedure is based the standard method of determining, on the one hand, the absolute right ascensions of stars, and, on the other, the local sidereal time of the place of observation.
In 1666 Auzout was one of a group of scientists making astronomical observations from Jean-Baptiste Colbert's Paris residence. In addition to Auzout the others involved were Christiaan Huygens, Pierre de Carcavi, Gilles de Roberval, Bernard Frénicle de Bessy and Jacques Buot. In many ways this can be seen as a meeting of the Académie des Sciences before its official foundation. Colbert, who was the French Minister of Finance, chose the small group who met in the King's Library on 22 December 1666, which was the founding meeting of the Académie Royale des Sciences. Auzout was one of these founding members and he quickly made a contribution. The records of the Academy contain the following:-
On the eleventh day of January 1667 M Auzout presented to the assembly a memoir which was read to the company on the observations that should be made at Madagascar.
This was the first known proposal for a scientific expedition and Auzout presented it to the Academy only three weeks after its first formal meeting. He clearly expected the Academy to get to work quickly. Olmsted writes:-
Auzout distinguishes astronomical observations which can be made anywhere, but which should be confirmed in the southern hemisphere, from those which can be made only in a place like Madagascar. Of the latter, those requiring corresponding or simultaneous observations at Paris are differentiated from those which may be made independently at Madagascar. The sixteen types of astronomical observations proposed constitute a comprehensive observational programme, adequate for a permanent observatory, and for the most part significant. In addition, some eleven terrestrial or physical observations are proposed, quite a number to be made during the course of the voyage to the island.
In fact Auzout, despite being one of the most vigorous in pushing for the opening of the Academy, was already showing frustration that things were not going as he had hoped. In the letter to Henry Oldenburg written on 28 December 1666, only a week after the first official meeting of the Academy (the letter we have already referred to above) he wrote :-
Although I had the honour to be appointed by the King as mathematician and physicist, I can't give you any more details than are known to everybody, because we have not been kept fully informed and things have not reached the point we were led to hope for. ... [during the summer of 1666] while we lacked instruments ... the constant hope of getting them [from the new Academy when it opened] resulted in individuals failing to undertake what they would normally have done.
A year later, on 29 December 1667, he again wrote to Oldenburg sounding fed up:-
I am hardly ever in a humour to write. I do not excuse myself with the weight of my work, because you may well believe I have none.
In 1668 Auzout resigned from the Académie des Sciences and left France. It is said that he had a disagreement, although no details are known, but it may simply be his disappointment that the Academy was not living up to his (perhaps ridiculously high) expectations of it. He had always had a strong interest in architecture and had spent much time with Christopher Wren when Wren visited Paris in the summer of 1665. Auzout had studied Vitruvius throughout most of his life and was fascinated by Roman architecture. It is therefore no surprise that he moved to Rome where he lived until his death in 1691. There he was well known for his particular interest in ancient architecture and engineering hydraulics. During his stay in Rome he was considered one of the real scholars of his day. He was the first to decipher the cancelled line on the Arch of Septimius Severus, in the Roman Forum, and served on the committee to tap the water of Lake Bracciano, 40 km north-west of Rome, for drinking water for the Acqua Paola fountain in Rome. Auzout did not completely cut himself off from his previous life, however, for when William Petty claimed that London was greater than Paris and Rouen combined, quoting population statistics to prove his case, Auzout responded vigorously in November 1686. The Petty-Auzout controversy continued for some time. Leibniz, in a letter written in December 1703, refers to Auzout being in Rome:-
I have learned that you intended to give me a copy of the 'Intellectual System' by the late Mr Cudworth ... The first time I saw this book was in Rome, where Mr Auzout, a French mathematician of great reputation, bought it ...
Article by: J J O'Connor and E F Robertson