[3] Born in Vyborg, he began a military career in Finland, but soon moved to Saint Petersburg to teach rational mechanics.
He tried to show their connections in his work Découvertes sur le cavalier (aux échecs), published in Saint Petersburg in 1837.
He wanted to take part in the London 1851 chess tournament, but arrived late and instead played a match with Howard Staunton, which he lost +2–7=1.
Staunton was most upset at his death in 1872, writing to Tassilo von Heydebrand und der Lasa in November of that year: I was sorry to lose Lewis and St. Amant, my dear friends Bolton and Sir T. Madden, and others of whom we have been deprived, but for Jaenisch I entertained a particular affection, and his loss was proportionately painful to me.
[7]After Jaenisch's death, a scholarship fund in his honor, which survives to this day, was established by his sister.