They thought to let the children learn the rules of play by observation.

Well, he'd soon know by observation, even though he could never experience it.

Maybe by observation you could tell me which of these is closer to the truth.

At least he should be able to figure out the command structure of this group, just by observation.

The only way to estimate either is by continuing observation.

However, the ability of animals to learn by observation and imitation is considered more significant.

It is by observation that we can judge the mood of people and animals.

Again, by observation, because the patients have to accept that when they are employing a new technology.

One can make out the difference among them by keen observation of the sculpture.

Only by experiment and observation can we learn something about the nature of the race.