The cannon

Two days later, Eldrian took a long break from the back-breaking practice. Unable to understand how just thinking and using magic, which was also thinking, could leave him drenched in sweat. 

So far he has gotten to the point where he can comfortably use Frost Needle along with Mana Examination. No longer limited to a few seconds, but rather nearly a full minute. 

This allowed him to learn more about how the mana was sent from his body to the icicle. He also went ahead and did the same with Vrachos, finding that the spell lasted far longer before requiring new mana. 

The most likely reason was that there was no need to keep the icicle cold. However, the difference felt too big for it to be just that.  Maybe the need to gather and form the ice?