[2] After Jacob's arrival at Bombay in 1831, he spent some years with the Great trigonometrical survey in the North-West Provinces, and established a private observatory at Pune in 1842.
He became assistant to Andrew Scott Waugh, but again fell ill.[3] In 1843 he went back to England on furlough, married in 1844, and returned in 1845 to India, but left the company's service on attaining the rank of captain in the Bombay engineers.
A transit-circle by William Simms arrived from England in March 1858, a month before he finally left the observatory, resigning on 13 October 1859.
[2] Jacob presented to the Royal Astronomical Society in 1848 a catalogue of 244 double stars, observed at Pune with a 5-foot Dollond's equatorial.
His re-observation of 317 stars from the same collection in 1853–7 showed that large proper motions had been erroneously attributed to them; the instruments used were a 5-foot transit and a 4-foot mural circle, both by Dollond.
The same volume contained 998 measures of 250 double stars made with an equatorial of 6.3 inches aperture constructed for Jacob by Lerebours in 1850.
Professor David Kipping states that the ‘“claim is so remarkable because Jacob was making tiny measurements (80 milliarc seconds or 22 millionths of a degree) with the naked eye, at a time when he wasn’t even sure whether Newton’s law of gravity held sway in distant parts of the galaxy.