the Deflections of the needle of a Galvanometer. 271 
imagine they would think otherwise if they had the habit of 
continued original investigation, or the proper ambition to 
address their students in the very language of Nature, by bring- 
ing them face to face with those phenomena which form the 
sure foundation of our scientific reasoning. 
The method, invented b Poggendorff, of observing the 
deflections of the daavenabition by —e to a screen a beam 
of light from a small mirror attached to the needles, has been 
used for many years, Sir William Thomson and Prof. Tyndall 
have extensively used this method; and it has the advantage 
of giving to the reflected beam an angular motion the double 
n 
