让·巴蒂斯特·约瑟夫·德朗布尔Jean-Baptiste Joseph Delambre

让·巴蒂斯特·约瑟夫·德朗布尔的父亲是一个布商。名字德朗布尔是“de Lambre”的一种形式，可能来自“lambeau”，意思是“破布”。他是父母孩子中的长子。当时的儿童疾病极其严重，当他15个月大时患上天花，他的父母一定怀疑他是否会有多大前途。由于这场疾病，他几乎失明，并且确实失去了睫毛，这些睫毛再也没有长回来。在他所有的肖像中，由于这一点，他有着相当不寻常的外貌，但通常，除非一个人意识到他没有睫毛，否则不会意识到他为什么看起来不寻常。鉴于他视力不佳，他从事天文学就更令人惊讶，但必须说，在天花之后的三十年里，他的视力继续改善。为了说明他20岁时视力仍然有多差，我们应该注意到，即使在那个时候，他几乎无法阅读自己的笔迹，也无法忍受直接阳光。

他在亚眠的耶稣会学院就读，师从雅克·德利尔神父，后者是一位诗人和古典学者。在那里，德朗布尔学习了英语和德语，但在1764年耶稣会被禁止在法国活动，此时他在亚眠继续接受教育，师从从巴黎请来的教师。当时他打算成为一名堂区神父，但这些新教师中的一位鼓励他去巴黎继续学业。他获得了巴黎普莱西学院的奖学金，在那里学习古典语言，为大学教育做准备。然而，当他参加大学入学考试时，视力不佳使他无法正确阅读试卷，未能获得奖学金。他的父母无力在没有奖学金的情况下送他上大学，因此鼓励他返回亚眠，但他留在巴黎试图自学。Claude Mathieu是德朗布尔的学生，他在Biographie universelle中关于他的文章中写道：-

人们必须听到这位谦逊而真诚的人讲述他离开普莱西学院后的生活方式，才会相信他在一年中花费的极少金额。

直到此时，德朗布尔几乎没有理由学习数学，但现在情况改变了。为了维持生计，他在贡比涅担任一位贵族儿子的家庭教师，现在他必须自学数学以便教他的学生。他很快成为专家，发展出非凡的计算技能。

1771年，德朗布尔回到巴黎，成为财政总收税官德朗布尔-Claude Geoffroy d'Assy之子的家庭教师。这对德朗布尔来说是个理想职位，因为他住在Geoffroy d'Assy家中，选择接受远低于d'Assy所给报酬的金额，接受了一小笔年金，乐于节俭度日，同时尽可能多地学习。此时，尽管他从未接受圣职，却自称Lambre神父。大革命时期，为避免贵族色彩，他将“de Lambre”改为“德朗布尔”。

德朗布尔的兴趣从研究希腊语和希腊文学转向希腊科学，他阅读了大量有关这一主题的著作。不久，他对希腊天文学的兴趣促使他去了解现代天文学，大约在1780年，他读了拉朗德的Traité d'astronomie Ⓣ（《天文学论》）。他开始在法兰西公学院听拉朗德的天文学讲座，并很快以其学识给拉朗德留下了深刻印象。1783年，当拉朗德为出版其Traité d'astronomie Ⓣ（《天文学论》）新版而寻找一位新助手来进行观测时，他找到了德朗布尔，后者是他最优秀的学生。拉朗德借给德朗布尔一些设备，他用这些设备收集的观测数据被纳入拉朗德的Traité d'astronomie Ⓣ（《天文学论》）第三版，该版于1792年付印。

1786年，德朗布尔记录了一次水星凌日。在预测的凌日时刻，天空有云，什么也看不见。大多数天文学家都放弃了，但德朗布尔没有，他不相信拉朗德预测的凌日时刻是正确的。当云在预测凌日结束四十分钟后散去时，德朗布尔得以观察到凌日仍在进行。正是意识到现有星表不准确，才促使他投入大量精力编制新的星表。

德朗布尔 出席了 Académie des Sciences 的一次会议，会上 拉朗德 展示了水星观测数据。在同一次会议上，皮埃尔·西蒙·拉普拉斯 宣读了一篇论文，介绍他的数学结果，该结果使得一颗行星对另一颗行星轨道产生的摄动可以被计算出来。德朗布尔 对此印象很深，决定对天王星的轨道进行观测，以验证 皮埃尔·西蒙·拉普拉斯 的理论结果。

拉朗德于1788年6月16日写给Bugge的一封信表明他对德朗布尔的印象有多么深刻：-

德朗布尔……目前是世界上所有国家中最有能力的天文学家。……我们必须鼓励这样宝贵的新人，并把他绑定在一门他无需指望任何职位或好处就能做出惊人成就的科学上。

当科学院宣布1789年的大奖将用于计算天王星的精确轨道时，德朗布尔已经完成了大部分工作。这个题目是由皮埃尔·西蒙·拉普拉斯和拉朗德考虑到德朗布尔而提出的，由让-多米尼克·德·卡西尼、拉朗德和皮埃尔·梅尚组成的委员会正式授予他该奖项，宣称他是：-

……一位富有智慧和毅力的天文学家，能够审视130年的天文观测，评估其不足之处，并提取其价值。

此时德朗布尔已经有了自己的天文台。1787年，Geoffroy d'Assy搬进了巴黎le Marais区巴士底狱以西的一所新房子，1788年，在拉朗德的鼓励下，他开始在这所房子顶楼卧室上方为德朗布尔建造一座天文台。这座配备了最新设备的天文台于1789年完工。

德朗布尔在他的天文台工作，1792年他出版了Tables du Soleil, de Jupiter, de Saturne, d'Uranus et des satellites de Jupiter Ⓣ（太阳、木星、土星、天王星和木星卫星的表）。Wilson在[10]和[11]中：-

……着手追溯月球与行星对地球运动的摄动被引入太阳表的步骤。这一发展过程中的主要里程碑是尼可拉·路易·拉卡伊1758年的表，以及德朗布尔的表，后者发表于拉朗德《天文学》第三版（1792年），还有经度局1806年出版的这些表的修订版。

弗朗索瓦·阿拉戈在谈到德朗布尔的工作时写道（例如见[1]）：-

在完善天文计算方法方面，他凭借其方法的多样性与优雅，理应在法国所能夸耀的最有能力的数学家中占据一个杰出位置。

同在1792年，德朗布尔第二次获得Académie des Sciences的大奖。他已于该年2月15日当选为Académie数学科学部的通讯院士。事实上，这是Académie des Sciences承担的一项重大工程，将在随后几年里占据他的精力，而他的当选恰逢其时。

Académie已于1790年成立了一个度量衡委员会，由让-夏尔·德博尔达、尼古拉·德·孔多塞、皮埃尔·西蒙·拉普拉斯、阿德里安-马里·勒让德和拉瓦锡组成，就度量衡的米制系统提供建议。经过一些方向上的变化后，它最终在1791年3月19日的一份报告中建议，该系统应基于定义为地球子午线四分之一的一千万分之一的米。该报告在一周后获得国民议会批准，剩下的就是计算子午线长度的更精确值。Académie des Sciences任命了皮埃尔·梅尚、阿德里安-马里·勒让德和让-多米尼克·德·卡西尼来执行这项任务。

决定使用三角测量法来测量敦刻尔克和巴塞罗那之间的那部分子午线，观测使用让-夏尔·德博尔达重复圆，这是一种极其精确的新仪器。这部分被分为两个不等的部分，敦刻尔克到罗德兹和罗德兹到巴塞罗那。北部部分要长得多，因为它在1740年已被塞萨尔-弗朗索瓦·卡西尼·图里精确测量过。尽管让-多米尼克·德·卡西尼热衷于负责该项目，但他拒绝亲自测量一个区段，于是在1792年5月5日，德朗布尔被赋予负责敦刻尔克到罗德兹区段的任务，皮埃尔·梅尚负责罗德兹到巴塞罗那区段。由于法国大革命和与法国邻国的战争，这项任务被证明比预期的要困难得多。

让-夏尔·德博尔达的重复圆仪图片见THIS LINK。

德朗布尔于6月出发，开始寻找巴黎周围的三角测量点。然而他在9月被捕，因为他的授权来自国王，而国王此时本人也已被捕。在获得新的官方文件后获释，德朗布尔不久后再次被捕，因为他的仪器被认为可疑，意味着他是间谍。他得以从巴黎的国民公会获得官方文件，继续他的任务。德朗布尔进展相对甚微，随后返回巴黎过冬，次年春天再次出发，开始从敦刻尔克向南推进。然而在1793年12月，他被公共安全委员会免除了子午线测量任务，该委员会下令（例如见[3]）：-

……政府官员[必须]仅将他们的权力和职能授予那些以其共和美德和对国王的憎恶而为人所知可信的人……

1795年5月，德朗布尔复职，并继续执行他十八个月前被迫突然终止的任务。1795年下半年，他在奥尔良和布尔日之间进行三角测量；1796年夏天，在布尔日和埃沃之间进行三角测量；1797年，他在埃沃和罗德兹之间进行三角测量，完成了他的任务部分。在这些三角测量任务之间，他于1795年12月前往敦刻尔克，并在1796年的头几个月计算了非常精确的纬度数据。还需要精确的基线测量，以便精确确定三角测量的尺度。德朗布尔于1798年4月在巴黎附近的默伦进行了精确的基线测量。

国际度量衡委员会成立，德朗布尔于1799年2月向其报告了他的结果。到那年6月，在皮埃尔·梅尚也报告之后，一根长度为1米的决定性铂棒被制成，成为公制的基础。整个项目的细节由德朗布尔在Base du système métriqueⓉ（公制的基础）中发表。三卷中的第一卷包含地球测量史和项目的三角测量数据，于1806年出版。当德朗布尔将其呈献给拿破仑时，皇帝说（[1]或[3]）：-

征服会来来去去，但这项工作将持久。

该著作的第二卷于1807年出版，包含敦刻尔克和巴塞罗那精确纬度计算的数据。1810年的第三卷探讨了计算中的误差和地球的偏心率。

约瑟夫·傅里叶为Académie des Sciences撰写了德朗布尔的讣告，他写道（例如见[1]）：-

……我们主要归功于他、而他承担最大份额的大地测量操作，是在任何国家执行过的最完美和最广泛的。它已成为此后所有此类项目的典范。

现在让我们看看德朗布尔职业生涯中的其他一些里程碑。1795年，他获准进入经度局，1800年成为局长。1801年，他被任命为Académie des Sciences的秘书，这使他成为法国科学界最有影响力的人物。1803年，他的健康状况恶化，患上了风湿热，但他继续将大部分时间投入到工作中。然而，1804年，他与伊丽莎白·德·波马尔结婚，她是他的助手的寡母。他们起初住在巴黎玛莱区的达西宅邸，除了外出旅行的时候，他从那里为他建造的天文台建成起就一直在那里进行观测。1807年，悲剧降临他的家庭，他妻子的儿子，此前曾是德朗布尔的助手，在那不勒斯去世，年仅26岁。然而，德朗布尔在职业生涯中取得了更多成就，包括1807年被任命为巴黎法兰西学院的天文学讲席。该职位一直由拉朗德担任，直到他于同年去世，德朗布尔为能接替他的前老师而感到自豪。1808年，他还被任命为帝国大学的司库，此时他与妻子从玛莱区的达西宅邸搬到了大学司库的官邸。

1809年，拿破仑要求Académie des Sciences为十年间最佳科学出版物颁发一项奖。该奖授予了德朗布尔，以表彰他关于子午线的工作。他还赢得了许多其他荣誉，无法在此一一列举。然而，我们应当提到，1815年他从公共生活中退隐后，被授予圣米歇尔骑士称号。此前，他已于1804年在巴黎荣军院举行的首次此类仪式上由拿破仑授予荣誉军团骑士勋位，1821年他又被授予荣誉军团军官勋位。

在职业生涯的最后阶段，德朗布尔对数学史和天文学史产生了兴趣。我们已经注意到，在Base du système métriqueⓉ（米制的基础）的第一卷中，他呈现了一部测量地球的历史。在他1789年的Rapport historique sur les progrès des sciences mathématiques depuisⓉ（1789年以来数学科学进展史）中，他于1808年2月向研究院宣读，并于1810年出版，他说：-

在几乎所有的数学分支中，人们都被不可逾越的困难所阻碍（但）我们时代的分析和力学的景象（使我确信）后代将不会在尚待完成的事情中看到任何不可能。

他于1817年出版了两卷本著作Histoire de l'astronomie ancienneⓉ（古代天文学史），然后于1819年出版了Histoire de l'astronomie du moyen ageⓉ（中世纪天文学史），1821年出版了两卷Histoire de l'astronomie moderneⓉ（现代天文学史），而他关于十八世纪天文学史的著作由Claude Mathieu在德朗布尔去世后出版。Grattan-Guinness在[5]中指出，他更多地是以计算天文学家的身份而非历史学家的身份来对待这一主题。这是公允的，因为德朗布尔并不认为自己在为历史学家写作，而是（例如见[1]）：-

……主要是为天文学家和数学家。

他说他的目标是产生：-

……一个宝库，在其中可以找到先后用于现象计算的所有思想、所有方法和所有定理。

Bernard Cohen 在 [1] 中写道：-

德朗布尔……按时间顺序逐一分析一部又一部论著，以此呈现每一个主要时期。……正如人们所料，德朗布尔 在天文表以及观测和计算方法方面尤为出色。其一大优点是关于次要人物的丰富信息，这些人物可能没有其他资料可查。最重要的是，德朗布尔 以尖刻而令人愉快的评论为他的叙述增添了趣味……毫无疑问，这部六卷本《历史》是任何科学分支中由单个人写出的最伟大的全面技术史。它树立了一个很少有科学史家能够达到的标准。

约瑟夫·傅里叶 在为 德朗布尔 写的讣告中写道（例如见 [1]）：-

在他之前，天文计算建立在数值方法之上，这些方法既间接又不规则。他彻底改变了这些方法，或者说巧妙地重新改造了它们。天文学家目前使用的大多数方法都属于他，这些方法是从解析公式推导出来的，在应用中已被发现同样可靠、统一且易于处理。

他因有一个大型月球环形山以他的名字命名而受到纪念。

Jean-Baptiste-Joseph Delambre's father was a draper. The name Delambre is a form of "de Lambre" which probably comes from "lambeau" meaning "rag". He was the eldest of his parents children. Childhood illnesses at this time were extremely serious and when he developed smallpox at the age of 15 months his parents must have doubted that he would ever have much of a future. He almost lost his eyesight as a result of this illness and he did lose his eyelashes which never grew in again. In all his portraits he has a rather unusual appearance because of this but often, unless one is aware that he has no eyelashes, one does not realise why he looks unusual. Given his poor eyesight it is even more remarkable that he took up astronomy, but it has to be said that his eyesight continued to improve during the thirty years following the smallpox. To give an indication of just how bad his eyesight still was when he was 20 years old, we should note that even at that time he could hardly read his own handwriting and could not bear to be in direct sunlight.

He attended the Jesuit College in Amiens, studying under the abbé Jacques Delille who was a poet and classicist. There Delambre studied English and German but in 1764 the Jesuits were banned from France and at this stage he continued his education in Amiens, studying under teachers who had been brought from Paris. At this time he was intent on becoming a parish priest, but one of these new teachers encouraged him to continue his education in Paris. He was awarded a scholarship to the Collège du Plessis in Paris and there he studied classical languages preparing himself for a university education. However, when he sat the university entrance examinations his weak eyesight meant that he could not read the examination paper properly and he failed to gain a scholarship. His parents could not afford to send him to university without the scholarship and so encouraged him to return to Amiens but he remained in Paris trying to educate himself. Claude Mathieu, who was a student of Delambre, wrote in his article on him in Biographie universelle:-

One would have to have heard this modest and sincere man giving an account of his way of life after leaving the Collège du Plessis in order to believe the tiny amount that he spent during one year.

Up until this time Delambre had little reason to learn mathematics but now this changed. To support himself he took a position as a tutor to the son of a nobleman in Compiègne and he now had to teach himself mathematics so that he could teach his pupil. He soon became an expert, developing exceptional calculating skills.

In 1771 Delambre came back to Paris where he became tutor to the son of Jean-Claude Geoffroy d'Assy, Receiver General of Finances. It was an ideal position for Delambre for he lived at in Geoffroy d'Assy's house and, choosing to accept far less in payment that d'Assy offered, he accepted a small pension and enjoyed living cheaply but learning all he could. At this time, although he had never taken holy orders, he called himself the Abbé de Lambre. He would change "de Lambre" to "Delambre" at the time of the Revolution to avoid its aristocratic appearance.

Delambre's interests moved from the study of Greek and Greek literature to Greek science, and he read much on the topic. Soon his interest in Greek astronomy led him to find out about modern astronomy and in about 1780 he read Lalande's Traité d'astronomie Ⓣ. He began attending Lalande's astronomy lectures at the Collège de France and soon impressed Lalande with his knowledge. When Lalande was looking for a new assistant in 1783 to undertake observations for a new edition of his Traité d'astronomie Ⓣ, he turned to Delambre who was his best student. Lalande lent Delambre some equipment and the observational data he collected with it was incorporated into the third edition of Lalande's Traité d'astronomie Ⓣ which would appear in print in 1792.

In 1786 Delambre recorded a transit of Mercury across the Sun. At the time which had been predicted for the transit there was cloud and nothing was visible. Most astronomers gave up, but not Delambre who did not believe that the time predicted for the transit by Lalande was correct. When the cloud cleared forty minutes after the transit was predicted to end, Delambre was able to observe that the transit was still taking place. It was the realisation that the existing tables were inaccurate which led him to devote much effort into producing new ones.

Delambre attended a meeting of the Académie des Sciences at which Lalande presented the data from the Mercury observations. At the same meeting Laplace presented a paper on his mathematical results which allowed the perturbations produce by one planet on the orbit of another to be calculated. Delambre was very impressed and decided to make observations of the orbit of Uranus in order to verify Laplace's theoretical results.

A letter which Lalande wrote to Bugge on 16 June 1788 shows how impressed he was with Delambre:-

Monsieur Delambre ... is currently the most able astronomer of any country in the world. ... We must encourage so valuable a recruit, and bind him to a science in which he performs prodigious feats without hope of any position or advantage.

When the Academy announced that the Grand Prix for 1789 would be for the calculation of the precise orbit of Uranus, Delambre had already done much of the work. The topic had been suggested by Laplace and Lalande with Delambre in mind, and the committee consisting of Dominique Cassini, Lalande and Méchain duly awarded him the prize, declaring him to be:-

... an astronomer of wisdom and fortitude, able to review 130 years of astronomical observations, assess their inadequacies, and extract their value.

By this time Delambre had his own observatory. In 1787 Geoffroy d'Assy moved into a new house in the le Marais district of Paris, west of the Bastille, and in 1788, encouraged by Lalande, he began building an observatory for Delambre above his bedroom on the top floor of the house. The observatory, fitted with the latest equipment, was completed by 1789.

Delambre worked in his observatory and in 1792 he published Tables du Soleil, de Jupiter, de Saturne, d'Uranus et des satellites de Jupiter Ⓣ. Wilson, in [10] and [11]:-

... undertakes to follow the steps whereby the lunar and planetary perturbations of the Earth's motion were introduced into solar tables. The principal landmarks in the development were the tables of Lacaille (1758), and the tables of Delambre that were published in the third edition of Lalande's Astronomie (1792), and the revised version of these tables published by the Bureau des Longitudes in 1806.

Arago wrote of Delambre's work (see for example [1]):-

In perfecting the methods of astronomical calculation he merits, by reason of the variety and elegance of his methods, a distinguished place among the ablest mathematicians France can boast.

In the same year of 1792 Delambre received the Grand Prix of the Académie des Sciences for the second time. He had already been elected an associate member in the mathematical sciences section of the Académie on 15 February of that year. In fact it was a major project undertaken by the Académie des Sciences which would occupy him for the next few years and his election came at precisely the right time.

The Académie had already set up a Commission of Weights and Measures in 1790 consisting of Borda, Condorcet, Laplace, Legendre and Lavoisier to advise on a metric system of weights and measures. After some changes of direction, it eventually recommended, in a report of 19 March 1791, that the system be based on a metre defined as one ten millionth part of one quarter of the Earth's meridian. The report was approved by the National Assembly one week later and it remained to calculate a more accurate value of the length of the meridian. The Académie des Sciences appointed Méchain, Legendre and Dominique Cassini to carry out this task.

It was decided to measure, using the method of triangulation with sightings made with the Borda repeating circle which was an extremely accurate new instrument, that part of the meridian between Dunkerque and Barcelona. This was divided into two unequal parts, Dunkerque to Rodez and Rodez to Barcelona. The northern part was much the longer since it had been accurately measured by Cassini de Thury in 1740. Although Dominique Cassini was keen to take charge of the project, he refused to personally measure one sector and, on 5 May 1792 Delambre was given charge of the Dunkerque to Rodez sector and Méchain the Rodez to Barcelona sector. The task proved much harder than anticipated because of the French Revolution and wars with France's neighbours.

A picture of the Borda repeating circle is at THIS LINK.

Delambre set out in June and began to seek triangulation points round Paris. However he was arrested in September since his authorisation came from the King who by this time had himself been arrested. Released after getting new official papers, Delambre was arrested again shortly afterwards since his instruments were thought to be suspicious and meant he was a spy. He was able to obtain official papers from the National Convention in Paris and continued his mission. Delambre made comparatively little progress before returning to Paris for the winter, then set out the next spring to begin working his way south from Dunkerque. In December 1793, however, he was removed from the meridian measuring task by the Committee of Public Safety who decreed that (see for example [3]):-

... government officials [must] delegate their powers and functions solely to men known to be trustworthy for their republican virtues and their abhorrence of kings ...

In May 1795 Delambre was reinstated and carried on the task he had been forced to end abruptly eighteen months earlier. He triangulated between Orléans and Bourges in the second half of 1795, between Bourges and Evaux in the summer of 1796, completing his part of the task by triangulating between Evaux and Rodez in 1797. Between these triangulation tasks he had travelled to Dunkerque in December 1795 and spent the first months of 1796 calculating very precise latitude data. Also required was an accurate baseline measurement so that the scale of the triangulation could be fixed precisely. Delambre made accurate baseline measurements in Melun, near Paris, in April 1798.

An International Commission for Weights and Measures was set up and Delambre reported his results to it in February 1799. By June of that year, after Méchain had also reported, a definitive platinum bar of length one metre was made to become the basis of the metric system. Details of the whole project were published by Delambre in Base du système métrique Ⓣ. The first of the three volumes, containing the history of measurement of the Earth and the project's triangulation data, was published in 1806. When Delambre presented it to Napoleon, the emperor said ([1] or [3]):-

Conquests will come and go but this work will endure.

The second volume of the work, published in 1807, contained the data for the accurate latitude calculations of Dunkerque and Barcelona. The third volume of 1810 looked at the errors in the calculations and at the Earth's eccentricity.

Fourier, who wrote an obituary of Delambre for the Académie des Sciences, wrote (see for example [1]):-

... the geodetic operation, for which we are chiefly indebted to him, and of which he bore the greatest share, is the most perfect and extensive which has been executed in any country. It has served as the model of all enterprises of the kind which have been since projected.

Let us now look at some other landmarks in Delambre's career. In 1795 he was admitted to the Bureau des Longitudes, becoming President in 1800. In 1801 he was appointed secretary to the Académie des Sciences making him the most powerful figure in science in France. In 1803 his health took a turn for the worse when he developed rheumatic fever but he continued to devote most of his time to work. However, in 1804, he married Elizabeth de Pommard, the widowed mother of his assistant. They lived at first in the d'Assy house in the le Marais district of Paris where, except for when he had been on his travels, he had continued to observe in the observatory above his room from the time it was first built for him. Tragedy struck his family in 1807 when his wife's son, who had previously been Delambre's assistant, died in Naples at the age of 26. Delambre attained further achievements in his career, however, including his appointment to the chair of astronomy at the Collège de France in Paris in 1807. The position had been held by Lalande until his death in that year and Delambre was proud to succeed his former teacher. He was also appointed treasurer to the Imperial University in 1808 and at this time moved with his wife from the d'Assy house in the le Marais district to the official residence of the Treasurer of the University.

In 1809 Napoleon requested that the Académie des Sciences award a prize for the best scientific publication of the decade. The award went to Delambre for his work on the meridian. He won so many other distinctions that it is impossible to list them all here. However we should mention that after he retired from public life in 1815 he was made a chevalier of Saint Michel. He had earlier been invested as chevalier of the Legion of Honour by Napoleon at the first such occasion in 1804 at the Hotel des Invalides in Paris, and in 1821 he was made an officier of the Legion of Honour.

In the last part of his career Delambre became interested in the history of mathematics and astronomy. We have already noted that in the first volume of Base du système métrique Ⓣ he presented a history of measurement of the Earth. In his Rapport historique sur les progrès des sciences mathématiques depuis 1789 Ⓣ, which he read to the Institute in February 1808 and published in 1810, he says:-

In almost all branches of Mathematics one is blocked by insurmountable difficulties (but) the spectacle of analysis and mechanics in our time (convinces me that) the generations to come will not see anything impossible in what remains to be done.

He published a two volume work Histoire de l'astronomie ancienne Ⓣ in 1817, then Histoire de l'astronomie du moyen age Ⓣ in 1819, two volumes of Histoire de l'astronomie moderne Ⓣ in 1821, and his work on the history of astronomy in the eighteenth century was published by Claude Mathieu after Delambre's death. Grattan-Guinness in [5] notes that he approached the subject matter more as a calculating astronomer than as a historian. This is fair, for Delambre did not see himself writing for historians, rather (see for example [1]):-

... mainly for astronomers and mathematicians.

He says that his aim was to produce:-

... a repository where could be found all the ideas, all the methods, and all the theorems that have served successively for the calculation of phenomena.

Bernard Cohen writes in [1]:-

Delambre ... presents each major chronological period in a series of discrete analyses of one treatise after another. ... As one would expect, Delambre is especially good on astronomical tables and on methods of observation and calculation. A great virtue is the wealth of information on minor figures, for whom no other account may be available. Above all, Delambre spices his presentation with acerb and delightful comments ... Unquestionably the six volume Histoire is the greatest full-scale technical history of any branch of science ever written by a single individual. It sets a standard very few historians of science may ever achieve.

Fourier wrote in his obituary of Delambre (see for example [1]):-

Before him astronomical calculations were founded on numerical processes, which were at one indirect and irregular. These he has changed throughout, or ingeniously remodelled. Most of those which astronomers use at the present time belong to him, having been deduced from analytic formulae, which, in their application, have been found alike, sure, uniform and manageable.

He is honoured by having a large lunar crater named after him.