Refractor, It's a refractor-esque telescope
Galileo discovered during his inclined-plane experiments that a ball rolling down an incline and onto a horizontal surface would roll indefinitely.
The rubber protects him from being electrocuted by the flow of current going through the plug.
Hope this helped!!
Answer:The frequency of the echo is slightly decreased
Explanation:
Given
speed of boat 
cliff is
away
when boat is still , suppose t is the time taken by the echo to reach observer on the boat
But as soon as boat starts moving the distance between cliff and boat decreasing and time for echo to reach observer also decreases
and we know 
therefore frequency of the echo slightly decreased.
You would see mountains off in the distance as if the earth was actually flat. but it seems flat because its so big