The only poem he published at this time was the famous Nicolai Klimii iter subterraneum (1741), afterwards translated into Danish by Baggesen.
The Iter subterraneum has been three several times translated into Danish, ten times into German, thrice into Swedish, thrice into Dutch, thrice into English, twice into French, twice into Russian and once into Hungarian.
It is thought to depend upon some connexion, not yet anatomically demonstrated, between the third cranial nerve and its nucleus in the floor of the iter and the substantia nigra.
The first modern scientific work is the Iter per patriam of Eggert Olafsson and Biarni Paulsson, which gives an account of the physical peculiarities - fauna, flora, &c. - of the island as far as could be done at the date of its appearance, 1772.
In their numerous allusions to the subtle mercury, which the one makes when treating of a means of measuring time by the efflux of the metal, and the other in a treatise on the transit of the planet, we see traces of the school in which they served their first apprenticeship. Huygens, moreover, in his great posthumous work, Cosmotheoros, seu de terris coelestibus, shows himself a more exact observer of astrological symbols than Kircher himself in his Iter exstaticum.
