Non-instantial hypothesis is a case of theoretical assumption where direct verification is never possible.
It is framed depending upon the knowledge gained in the field of science at a developed stage in order to establish an order among the theories.
It systematizes the generalisations by help of a higher theory. Observation of fact is not available here.
This category of hypothesis is mostly used in case of secondary induction. For example, Maxwell reached at the electromagnetic theory of light through a non-instantial hypothesis.
Einstien’s theory of relativity is also an instance of non-instantial hypothesis.