Bauhaus-Universität Weimar

The Art of Projecting. A Manual of Experimentation in Physics, Chemistry, and Natural History with the Porte Lumière and Magic Lantern
Dolbear, A. E.
with the thumb and finger, fine iron filings upon the 
glass. The filings will arrange themselves in the 
familiar lines called the magnetic phantom, and the 
whole being magnified to ten feet or more in diameter 
makes a very striking picture. 
5. The elongation of an iron rod when strongly 
magnetized, may be shown by placing a small helix 
around the iron rod of the common pyrometer made 
for showing the longitudinal expansion of a rod by 
heat. To the end of the index finger that sweeps over 
the quadrant affix a small bit of plane mirror not more 
than one fourth of an inch square. So adjust the light 
to this small mirror that the reflection from the latter 
will fall upon the most distant part of the room ; the 
farther away the better. When the current of elec¬ 
tricity is sent through the helix the rod will be slightly 
elongated, but the slight tilting of the mirror may 
become a displacement of two or three inches at a 
distance of thirty feet. 
The electro-magnet for demonstrating diamagnetic 
phenomena need not be over three or four inches in 
length, and the poles an inch apart. 
Objects to be tested may be suspen¬ 
ded by a thread between the poles, 
and the whole projected either in a 
beam of parallel rays or in front of 
the focus of a lens. In the latter 
case the whole will be seen in pro¬ 
file, but perfectly distinct. The fol¬ 
lowing experiments may be projected 
with such a magnet if a battery of 
three or four cells be used : —


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