[1] He was Director of the Brazilian National Observatory from 1881 to 1908, led the commission charged with the survey and selection of a future site for the capital of Brazil in the Central Plateau,[2] and was co-discoverer of the Great Comet of 1882.

[3] Cruls was also an active proponent of efforts to accurately measure solar parallax[2] and towards that end led a Brazilian team in their observations of 1882 Transit of Venus in Punta Arenas, Chile.

Likely inspired by Brazilian friends at University (including Caetano de Almeida Furquim, a fellow engineer), Cruls resigned his commission and set out for Brazil on 5 September 1874.

[5] This latter meeting led to Cruls being hired as an engineer by the Commission of the Empire General Charter (Comissão da Carta Geral do Império)[6] in the Geodesy section.

[11] The Cruls made their home in the Rio neighborhood of Laranjeiras[7] and had six children: Edmée, Stella, Sylvie, Maria Luísa, Henri (who died as a child), and Gastão.

[6] Liais had become worn down by public accusations of scientific incompetence and dishonesty from Manoel Pereira Reis (an astronomer he had dismissed as head of the Commission of the Empire General Charter in 1878) and returned to Cherbourg, France.

[3] In that single year, Cruls co-discovered the Great Comet of 1882,[7] led a Brazilian expedition in observations of the 1882 Transit of Venus,[4] and received the Valz Prize from the French Academy of Sciences.