Ces investigations durerent plus de vingt minutes ; tantôt Holmes mesurait, avec une minutie extreme, la distance entre deux traces qui restaient totalement invisibles a mes yeux ; tantôt il appliquait son metre contre le mur d’une maniere tout aussi incompréhensible.
For twenty minutes or more he continued his researches, measuring with the most exact care the distance between marks which were entirely invisible to me, and occasionally applying his tape to the walls in an equally incomprehensible manner.