Word: fractions
(lookup in dictionary)
(lookup stats)
Dates: during 1930-1939
Sort By: most recent first
(reverse)
...make bigger and better mirrors for the telescopes. Glass, which has long been used for the smaller mirrors, is almost out of the question for a really large project. The reason for this is that the surface curvature of these reflectors must be correct down to a fraction somewhere between a quarter to a half millionth of an inch...