ro ELEMENTS OF APPLIED MICROSCOPY. 
edge, the first distinct advances were made in Arabia. 
Alhazen, the great Arabian physician of the eleventh 
century, distinctly describes the use of lenses for pro- 
ducing enlarged images, in a publication supposed tc 
date from about 1os2. Two centuries after, Roger 
Bacon, the Franciscan monk, and noted alchemist, of 
Oxford, noted the same effect. A little later, near the 
end of the thirteenth century, lenses were first applied 
to the mitigation of defects of vision; and to Salvino 
d’Armato degli Armati,.a Florentine, the invention of 
spectacles is ascribed. The use of lenses as microscopes 
for the examination of objects too minute to be studied 
with the unaided eye became general about the end of 
the sixteenth century. From the year 1600 such obser- 
vations were numerous, and in 1637 the first diagram of 
a microscope now extant was published by Descartes. 
About 1665 small glass globules began to be used instead 
of convex lenses for the simple microscope. They were 
set in metal plates, on the side of which opposite to the 
observer the object to be examined was mounted on some 
sort of movable arm. With these instruments a high 
magnification was obtainable; and it was with such 
simple microscopes (Fig. 9) that the pioneer microscopists 
of the seventeenth century, Kircher in Italy and Leeuwen- 
hoek in Holland, founded the science of Micro-Biology. 
8. The Compound Microscope.—Meanwhile a step 
had been taken, which, though not particularly fruitful 
at the time, was to become later of great significance. 
This was the invention of the compound microscope, 
commonly attributed to the Dutch spectacle-makers, 
