There should be no 'and' in there. The sentence should go like this:
The man is a scientist with a keen sense of observation who dedicates long hours in the lab.
The basis for historical knowledge is not empirical facts but written text, observation alone is not sufficient
Observations
The job of a scientist is to study natural phenomena with the aim of understanding and perhaps utilizing these occurrences. The study of earthquakes is seismology, and a scientist who studies them is a seismologist.
The subject is the word (noun or pronoun) that the sentence is about.
The adjective in the sentence "you love the blue sky" is "blue". It describes the noun "sky".
I can give you several sentences.Careful observation will reveal that the burglar had a key.The scientist began his observation of the strange rock.You powers of observation are amazing.
Thank you for your astute observation.
Annie was making an observation about beautiful stars in the dark pitched sky. The astronomer was making an observation of one of those stars. The accident victim had no apparent serious injuries, but was placed under observation.
The basis for historical knowledge is not empirical facts but written text, observation alone is not sufficient
The verb in that sentence is describes.
Scientist
the scientist chewed bubble gum :)
Scientists often find that quantitative observation is more important than qualitative observation.
Example sentence - He studied many hours to become a scientist and was well rewarded for his efforts.
Systematic Observation was one suggestion given to the employer by the manager. This is an example using the word systematic observation.
The best description of a scientific theory is the last one that you offered, that it is well tested and it explains a wide range of observation.
a descriptive sentence is a sentence that describes something in one sentence