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weeks or months. He collected all the reli-
able observations of comets he could find, to
the number of twenty-four, and computed
their parabolic orbits by the rules laid down
by Newton. His object was to find out if
any of them really travelled in elongated el-
lipses, practically undistinguishable, in the
˜
visible part of their paths, from parabolA,
in which case they would be seen more than
294