In Search of the Castaways

The book tells the story of the quest for Captain Grant of the Britannia.

After finding a bottle cast into the ocean by the captain himself after the Britannia is shipwrecked, Lord and Lady Glenarvan of Scotland contact Mary and Robert, the young daughter and son of Captain Grant, through an announcement in a newspaper.

Moved by the children's condition, Lord and Lady Glenarvan decide to launch a rescue expedition.

The main difficulty is that the coordinates of the wreckage are mostly erased, and only the latitude (37 degrees) is known; thus, the expedition would have to circumnavigate the oceans on the 37th parallel south... (Excerpt from Wikipedia)