many thanks Raymott.
but may i ask what are other possible meanings of this phrase?
for example in this sentence :
Other possible meanings are anything consistent with dictionary definitions of 'endowment' or 'to be endowed with something'.
From there, you need to take the meaning from the context.
So, in the original, you need to ask yourself, "What are the endowments that a natural scientist should have that would make it improbable that he would drift off from a concrete study of science as found empirically in nature, into a philosophical speculation about the nature of epistemology?"
As I implied, my initial reading was something of a guess. But he has to be endowed - by birth or education - with a mind that accepts knowledge empirically from nature, not through mere thought. (meaning 2 in the dictionary entry below).
In your second sentence, the endowment is perhaps more physical. (meaning 1).
Cambridge:
endowment noun
/ɪnˈdaʊ.mənt/ n
•
[C or U] money that is given to a college or hospital, etc. in order to provide it with an income, or the giving of this money
The school has received an endowment of £50 000 to buy new books for the library.
•
[C] something that you have from birth, often a quality
There are tests which can establish a baby's genetic endowment.