In the 1860s Victor Puiseux took his five children on vacations in the French mountains where they all enjoyed very long walks. Although only a young lad, Pierre loved this time in the country and mountainside. Some years they went to the Alps, some years to the Pyrenees. While on these holidays, Victor Puiseux would write to Sophie Jannet, Pierre's maternal grandmother, and these letters show how grateful he was for her support with his family. Pierre, whose studies were all in Paris, began his school studies at the Lycée Henri IV, then entered the Lycée Saint-Louis in 1865. Augustin Boutan (1820-1900), professor of physics and Headmaster of the Lycée, was a friend of Victor Puiseux. Another tragedy struck the family soon after Pierre entered the Lycée Saint-Louis when his brother Paul Puiseux died of typhoid fever in January 1866. Pierre was ten years old and losing his older brother must have been devastating.
Soon after the death of Paul, the family moved to 81 Boulevard Saint-Michel, where Sophie Jannet also took an apartment. She died at the age of 93 in 1874. In 1867, now with four children, Victor Puiseux went for the summer holiday to Switzerland, to the small village of Engelberg, in the Bernese Alps. On 7 September Victor Puiseux, Pierre and his two older sisters, made an ascent of the Titlis, a mountain of 3240 metres. It is remarkable to think that Pierre, only twelve years old at the time, could make such an ascent. We are lucky to have a record of Victor Puiseux's own description (see ):-
Awakened before midnight, I called Pierre, Louise and Marie, who rose without being asked. We descend with as little noise as possible, and at the foot of the staircase we find our guides, Leodegard Feierabend and Giuseppe Cattani, each carrying a lantern with one hand, and the other with an axe whose handle serves as a steel-tipped stick; they also provided us with ropes, and each of them has on his back a bag containing provisions. Clouds cover much of the sky; we see only a few stars towards the north. We leave without being reassured about the weather, and after crossing the bridge in front of the village, we begin to climb into the forest.Soon they are climbing through rocks and snow:-
About four o'clock we notice a rock which shelters us against the wind and in the crevices of which there is a fairly mild temperature. It is here that we make our first breakfast, above a frightful precipice in which a guide enjoys rolling stones.They continue to climb through difficult terrain:-
Pierre and Marie are tied to the guide who walks at the front. Another rope ties Louise, the second guide and myself, the guide was in the rear and Louise between us. At last we arrive at the critical spot where it is no longer snow that we have under our feet, but a slope of hard ice leading to precipices.They reach the summit, enjoy the scenery, and do not begin their return until midnight, arriving back at their hotel in time for lunch the next day "a little tired but delighted with our expedition."
Often on such climbs Pierre and his father would stop and sketch the scene before continuing. This experience gave Pierre a life-long passion for mountaineering.
In 1870, when Pierre was fifteen years old, the family took their summer holiday in the Pyrenees without André, and on their return in September they stopped at Lectoure, where Augustin Boutan, Pierre's headmaster, had a holiday home. The French army had suffered defeats in the Franco-Prussian war which began on 19 July and Prussian troops were approaching. Victor Puiseux returned to Paris with his two daughters, leaving Pierre with the wife of Augustin Boutan in Lectoure. Pierre quickly became good friends with the Boutan children. Over the winter, the mathematics teacher at the local Lycée was absent due to the war and Pierre took over teaching mathematics at the school. After the armistice at the end of January 1871 Pierre returned to Paris and continued with his schooling at the Lycée Saint-Louis. His sister Marie, who had become ill during the Paris siege, died from tuberculosis in March 1872. Around this time his other sister Louise also became ill; she died in May 1874. Remarkably, every summer, including the years when the girls died, Pierre with his brother André and their father, went climbing in the mountains.
In 1875 Pierre sat the entrance examinations in mathematics for the École Normale Supérieure and later that year he began his studies there. However, he also attended lectures at the Sorbonne, for example the attended Jules Tannery's lecture course there in 1876. His passion for mountaineering became even greater and he continued to tackle the hardest peaks every summer. For example, Pierre and André climber the Dard in 1876, Victor, Pierre and André reached the summit of the Chasseforêt on 1 September 1876, André and Pierre climber the Labby on 4 August, and Pierre climbed the Arpont on 20 August 1876. Pierre's book  and  give details of all his mountaineering exploits.
He obtained his aggregation in mathematics in 1878 and presented his doctoral thesis Sur l'accélération séculaire du mouvement de la lune. Suivi de Propositions données par la faculté to the Faculty of Science in 1879. This important work was published in the same year and Pierre was awarded his doctorate. However, the family had always been highly religious and, after the award of his doctorate, Pierre decided to change career completely and study divinity. He wrote to the minister of education on 29 October 1879 :-
... having entered the École Normale in 1875, I was soon convinced that the path I had taken was not the best one for my tastes and for the nature of my spirit. Wishing to follow an obvious vocation and to serve my country more effectively, I have come to ask you for permission to begin my ecclesiastical studies at the seminary of Saint-Sulpice.The minister replied to the director of the École Normale on 7 November :-
I have the honour to inform you that I do not put any obstacle to the resolution of M Pierre Puiseux.However, at this point the family must have put pressure on Pierre to change his mind and to continue to follow a scientific career. Pierre's uncle Léon Puiseux, who was inspector general of primary education, wrote to the director of higher education on 11 November :-
My nephew, agreeing to the request of the members of his family, sacrificed what he considered to be his vocation and renounced the resolution he had taken.On 20 November, Pierre applied for admission to the Paris Observatory as a student-astronomer, and was accepted on 1 December 1879. He was promoted to assistant astronomer in 1881. He was sent to Fort de France, in Martinique, in 1882 for the observation of the transit of Venus. This was one of ten expeditions organised by the Academy of Sciences to observe the transit which took place on 6 December 1882, other expeditions going to Haiti, Florida, Cape Horn and Mexico. Pierre Puiseux was part of the Martinique expedition headed by Felix Tisserand (1845-1896) which also included Guillaume Bigourdan (1851-1932). Pierre Puiseux published Note sur le passage de Vénus de 1882 in the Connaissance des temps ou des mouvements célestes à l'usage des astronomes et des navigateurs published by the Bureau des longitudes.
Pierre Puiseux married Beatrice Elise Marie Bouvet (1861-1963) in Salins on 21 June 1883. Beatrice Bouvet was the daughter of Alfred Bouvet (1820-1900) and his second wife Esther Billet. Alfred Bouvet, who came from Salins, was from a wealthy family who had made their fortune from transport companies. He presented the newly married couple with property at Frontenay, a village on the edge of the Jura. There were two large houses set among vineyards. Pierre and Beatrice had six children: Marie-Louise Puiseux (1884-1970); Victor Marie Puiseux (1887-1978); Madeleine Marie Puiseux (1888-1983); Robert André Jean Joseph Puiseux (1892-1992); Marguerite Marie Adele Puiseux (1894-1984); and Olivier Henri Frederic Puiseux (1899-1947).
He continued to be promoted at the Paris Observatory, being made an associate astronomer in 1885. He also had other positions, however for the book Leçons de Cinématique. Mécanismes, Hydrostatique, Hydrodynamique which he published in 1890 was based on lectures he had given at the Sorbonne. He describes himself on this book as an assistant lecturer at the Faculty of Science in Paris.
He had held this position at the Faculty of Science since 1880 and in 1897 he became an honorary professor there. In 1904 he was promoted to the position of astronomer at the Paris Observatory and, in the same year, he was appointed as professor of celestial mechanics at the Paris Faculty of Science and gave a course on celestial mechanics at the Sorbonne. He also gave a course on celestial mechanics at the Sorbonne from 1909 until 1917.
We have emphasised above the important part that mountaineering had in Pierre Puiseux's life but this was not just a hobby. From the very earliest times when he climbed with his father and other family members he had been fascinated by the geology of the rocks that he was clambering over. This meant that when he became an astronomer, he became interested in the moon for he saw there rock formations and wanted to understand the geology of the moon. At the Observatory he worked with the astronomer Moritz (Maurice) Loewy (1833-1907). Loewy, born in Vienna of Jewish parents, escaped the persecution of Jews in his home city and moved to France where he was employed at the Paris Observatory. In 1781 Loewy proposed a revolutionary new type of telescope, the Equatorial Coudé, and the director of the Observatory, Charles Delaunay, was extremely positive about the idea. However Delaunay died in 1872 and the Equatorial Coudé project was put on hold. In 1882, Loewy with Pierre Puiseux as his assistant, began working on the design and construction of the telescope. Their first Small Equatorial Coudé had a 10.5 inch (27 cm) objective and performed exceptionally well. They then worked on building the Grand Equatorial Coudé, a 23.6 inch telescope, which they completed in around 1891. Maurice Loewy and Pierre Puiseux published a description of this work in their book Théorie nouvelles de l'équatorial coudé et des équatoriaux en général published in 1888.
The major work that Loewy and Pierre Puiseux undertook with the Grand Equatorial Coudé was their monumental Atlas Photographique de la Lune . This required fourteen years to complete between 1894 and 1909 and in fact Loewy died in 1907 so Pierre Puiseux headed the project on his own in its final stages. They took :-
... over 6000 photographic plates of the Moon covering the whole portion visible from the Earth. Because perfect weather conditions were needed, the project took 14 years to complete. During this period only 50 or 60 nights per year exhibited the ideal weather conditions, and from those nights suitable for photography only 4 or 5 usable plates were taken.
In April 1904 the Bureaux des Longitudes proposed to French observatories that they organise expeditions to observe the total solar eclipse which would occur on 30 August 1905. The Paris Observatory sent an expedition to Cistierna, Léon, Spain led by Pierre Puiseux and also involving Maurice Hamy, Charles Le Morvan, Jules Baillaud and Georges Prin.
In 1908 Pierre Puiseux published the book La terre et la lune : forme extérieure et structure interne giving his theory regarding the craters on the moon. He believed that the craters were mostly caused by internal mechanisms, a theory which has turned out to be incorrect since we now know that most of the craters are the result of external bombardment.
Sadly he began to suffer serious health problems and from 1913 onwards could not even walk in his beloved mountains due to severe arthritis. However, he still spent his summers sitting in a place where he could see the mountains. Even his work at the Observatory was only possible with great difficulty and considerable suffering.
His astronomical contributions are summed up in :-
At the Observatory he was associated with Loewy in the construction of the Equatorial Coudé and on the observations made with it. The first work with this instrument was a determination of the constant of aberration. The principal work carried out by Loewy and Puiseux was on lunar photography. Over 6000 plates of the moon were taken. These were carefully examined by Puiseux, who made the enlargements from which the fine atlas of seventy-one sheets was constructed. It was Puiseux also who wrote the descriptions and discussed the results. This naturally led him to consider the "geology" of the moon. He reached the generally accepted opinion that the lunar formations can be explained as the result of stresses set up at the solidifying surface of an originally liquid sphere, and not through the action of outside forces. He has given in great detail his ideas of the progress of events in the cooling and gradual solidification of the moon. The difference between terrestrial and lunar mountains was attributed by him to a folding of layers on the earth and a rupture of the surface of the moon. In his final work he discussed the oscillation of the moon about its centre of gravity.Pierre Puiseux received many honours. He was awarded the Valz Prize by the Academy of Sciences in 1892, the Lalande Prize of the French Astronomical Society in 1896, and the Janssen Prize from the Academy of Sciences in 1908. He was made a knight of the Legion of Honour in 1900. An active member of the French Astronomical Society, he was elected president in 1911. He was elected to the Astronomy Section of the Academy of Sciences in 1912, and was elected an associate member of the Royal Astronomical Society in 1917. Not surprisingly, he was an enthusiastic member of the French Alpine Club which elected him honorary president.
He died in 1928 after many years of great suffering. His wife Beatrice survived him by thirty-five years, living to be well over 100.
Article by: J J O'Connor and E F Robertson