SCIENCE AND INDUSTRY. 
The early lenses were not of very great magnifying power, and 
Leeuwenhoek (1632-1723) appears to be the first to succeed in grinding 
and polishing lenses of such short focus and perfect figure as to render 
the simple microscope he made much better than any other instrument 
then known. These lenses he mounted between two plates, and to the 
plates he fastened a needle, with the object to be examined at the point 
of it, and in the focus of the lens. In the case of liquid, he placed a 
drop on a fine little plate of tale. Each instrument was complete with 
its own lens and object, and he bequeathed many of them to the Royal 
MIXED DIATOMS. THE SKELETONS OF TINY ANIMALS, MILLIONS BEING 
_. FOUND IN DIATOMACEOUS EARTH. 
Seventy Times Natural Size. 
Society, London. He must have been gifted with rare powers of obser- 
vation, for with these simple magnifying glasses he discovered the active 
principle (theine or caffeine) of tea and coffee, and described the 
cellular structure of the coffee berry, and mentioned the oil drops. In 
vinegar he noticed that there were often minute “cels,’ which he 
described and figured. Thus Leeuwenhoek may be given the honour of 
having made the first microscope examination of food substances. 
Two other great workers at that time were (1) Dr. Hy. Power, who 
published some microscopic observations on sand, sugar, salt, vinegar eels, 
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