Helen Kirsch, age 16, of Brooklyn, ,Y., or her question:

How many locks has the Panama Canal?

he Isthmus of Panama is a neck of land about 40 miles wide. On one side is the Atlantic, on the other side is the Pacific. On the isthmus is Gatun Lake, which is 85 feet higher than the level of the two oceans.

The 50‑mile canal joins the two oceans, but in doing so it makes use of Gatun Lake, which is above sea level ship passing through the canal must be raised 85 feet. This job is done by three locks. The ship sails over the lake and then must be lowered 85 feet. This job is done by three more locks. On a journey through the canal, a ship passes through six locks.

Meantime traffic is carving in the opposite direction. The canal is made for two‑way traffic. Six locks are necessary for eastbound traffic and six for west bound traffic. Altogether the canal has twelve locks. The locks are arranged in pairs, one for each traffic lane. Each lock is a concrete trough 2000 feet long and 110 feet wide.