11.   The truth of such statements is to be established by careful observation.

12.   This was probably based on careful observation of the summer solstice.

13.   Careful observation suggests that this is not the case.

14.   ...careful observation of the movement of the planets.

15.   It is an applied science founded on the careful observation of the natural world coupled with the application of physical, chemical and biological concepts to explain Earth processes.

16.   It takes careful observation and probing, he said, to solve the mystery.

17.   Large, leafy maples continue to flourish in the infield, making for a sylvan scene, but careful observation of the races is a challenge.

18.   Others are rooted in the careful observation of nature.

19.   She noted these along with careful observations of the habitats.

20.   That Virginia home is a legacy of his careful observation of the Paris mansion.