332 THE AMERICAN MONTHLY [Dec 
Pearlite, a mixture of cementite and ferrite. 
Martensite, the structure of quenched steel. 
Austenite, a name given to structure which is produced 
in steelin which there is a high proportion of carbon. 
There is vastly more to be learned of this interesting 
subject, and it is a field in which the amateur could with 
interest and profit make investigations. 
MULTIPLIED ImAGeEs IN DiatToms.—Happening to hold a 
needle over the mirror of the microscope while a slide of 
Triceratium was under examination, I noticed that its 
point appeared dimly in each of the interspaces, and on 
racking the body of the microscope slightly upwards in 
same manner as is necessary when observing multiplied 
images in the cornea of the eye of a beetle, I noticed that 
it became distinctly sharp. I then placed a piece of black 
paper cut in the shape of a cross on the mirror, and with 
a 1-6 in. objective saw it sharply displayed, although on a 
much smaller scale than in the eye of beetle. 
Experiments were then made with Coscinodiscus and 
other diatoms, and the same result was shown. ‘This 
would seem to indicate that these interspaces are lenticu- 
lar in shape, and it may be that with this knowledge fur-- 
ther light may be shed on the complex question of the 
ultimate structure of some of the Diatomaceez. 
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