This deaf-and-dumb servitor was driven mad by a fact which caused him joy.

Why?
12.

Notice the following schedule.

It has been drawn up after repeated experiments with Bartow and the various slides of the strange lamp which cause so many different lights to shine out in Mr.Adams's study: White light--Water wanted.
Green light--Overcoat and hat to be brought.
Blue light--Put back books on shelves.
Violet light--Arrange study for the night.
Yellow light--Watch for next light.
Red light--Nothing wanted; stay away.
The last was on at the final scene.

Note if this fact can be explained by Mr.Adams's account of the same.
With these points in our mind, let us peruse the history of this crime and of the remote and possibly complicated causes which led to it..