Why do you think Stevenson interrupts the sequence of events in order to provide us with Dr. Livesey's narration in Ch. 16-18? What is the purpose of this added perspective?

The major difference between Chapter Sixteen and the previous ones is the shift in narration, from Jim Hawkins to the Dr. Livesey. This shift was necessary in order to ensure that a first-hand account can be told of the events that Jim was not a witness to, because he was on land. Within the narration, there are certain clues that that Jim is no longer the narrator, including comments about places that might be likely breeding places for disease and comments concerning his time in the military.

It is also interesting to contrast the two different narration techniques. First, Jim's technique allows the reader to gain much more insight into the feelings and emotions that he feels, a typical aspect given his young age. Livesy, whose account is very factual and contains plenty of detail, does not let the reader into what he is thinking or feeling, on the other hand. A good example of this is Livesey response when he believes that Jim has been killed. The only thing that he does is report that "Jim Hawkins is dead," and then simply moves on.