observational knowledge

Physics, mathematics, and observational telescopic astronomy. The latter, observational astronomy, he practically invented.

C. V. Platt has written:

'An observational study of science teaching in school laboratories (OSOST)' -- subject(s): Science, Study and teaching

In painting, yes. But a drawing can also be observational.

Basically, all science is experimentation, but what I think you are talking about is, observational science is where people gather information without changing any of the variables of the natural environment. Examples could be, watching for how long a Guinea pig's gestation period is, or when cats generally give birth to kittens. Experimental science is where the testing group is in a laboratory, or in the natural environment, but some of the natural variables have been changed or altered. Examples could be, discovering the patterns of nuclear fission in the atomic bomb, or giving half of an experimental plant species light, and the other half no light.