The mean proportion of $\frac{1}{2}$ and 128 is _______.

The mean proportion is the square root of the product of numbers given.

Therefore, according to the given data 

The mean proportional between $\frac{1}{2}$ and 128 is:

$=\sqrt{\frac{1}{2}\times 128}$

$=\sqrt{\frac{ 128 }{2}}$  

$= \sqrt{64}$

$= 8$