Not long ago we had an opportunity of seeing the tests with the pendu lum which, according to the theory of the widely-known physicist, Mr. Leon Foucault, are 'said to furnish the proof of the daily rotation of the earth upon its axis. I had well-nigh failed to take any notice of those Pendulum tests. Although, when explaining to my pupils, boys and girls, in my geo graphical and physical lessons, the revolution of the earth about the sun, I had always found one point (which you will learn in the course of my lecture) very strange - may, incomprehensible - yet I was so convinced of the daily rotation of the earth, and its yearly course round the sun, as to deem Mr. Foucault's pendulum-proof entirely superfluous. Nevertheless, I was present at the experiment, and I will explain it in a few words, to make the application clear.