Why couldn't Axel persude his uncle to give up Journey

because he felt that his uncle didn't sleep or eat and also his uncle insisted on his disition and his uncle appreciate the values of science.

Because his uncle was obssessed with science

because his uncle is famous scientist and he needs to search for him self

Because The professor was sure that the inside of the earth can't be very hot , so he saw it was possible to make that journey as long as it is not hot under the earth.