According to Bicchierai (X2), Mossotti left Italy with one of the Ciani brothers, who offered to take him to England with him; then he stayed in Switzerland, and finally he went to London passing through Paris. Bicchierai doesn't mention any date. In Codazza's opinion (X1), he went to Geneva and then to Rogoreto, in the Grigioni district, and then went to London with Giacomo and Filippo Ciani. Codazza mentions that the date of his arrival in London is 1825.
In 1826 Mossotti sent a letter to de Cesaris in order to resign from his job at the observatory. The letter is dated 1 August 1826 and came from Orpington, in south-east London. De Cesaris informed the Government about Mossotti's resignation in order to be able to promote E. Brambilla to First Pupil. The Government replied with a notice of dismissal of Mossotti.