The final solo in this book is a short example of acoustic slide guitar. All the notes in this piece apart from the open strings are played using a slide, a piece of tubing placed on the little finger of the left hand. Also called a "bottleneck", the slide can be made of glass, steel or brass. The slide is used often in Blues guitar styles.
Although most slide guitar is played using open tunings, this solo is in standard tuning, as it is only a brief introduction to slide guitar. For more on this style see Progressive Slide Guitar Technique and Progressive Slide Guitar Licks by Brett Duncan.