This was a strange move since he was immediately deprived of the academic environment of Bordeaux. However, several trips abroad saw his became friends with other notable historians of science such as Heiberg, Zeuthen and Moritz Cantor .
Ito ay isang kakaibang ilipat mula noong siya ay agad-agad na bawian ng mga akademikong kapaligiran ng Bordeaux. Gayunman, ang ilang mga biyahe na nagtatagal sa ibang bansa nakakita ng kanyang naging kaibigan sa iba pang mga tanyag historians ng agham tulad ng Heiberg, Zeuthen at Moritz kantor.