272 A. M. Mayer— Device for projecting on a Screen 
tion and of limited applications when compared with the very 
simple apparatus I will now proceed to describe. 
G is the glass shade of the galvanometer, on which, at g, are 
drawn in india-ink the vertical graduation lines of the instru- 
ment. is a piece of aluminum wire to whose lower end are 
fixed the needles of the galvanometer, and whose upper end is 
perforated with a small hole so that the system may be suspended 
by a silk fiber. A fine wire of german-silver, w, is attached 
transversely to thealuminum wire, and has its ends bent down- 
ward at right angles to its length. This transverse wire can be 
placed at any azimuth by rotating it around its center, which is 
coiled two or three times around the vertical aluminum wire. 
On one of the bent ends of the transverse wire is cemented a 
nish, and ese 
lines are illuminated by the lantern, and in front of them 18 
