If you downloaded Garcia's Complete Treatise on the Art of Singing at the IMSPL/Petrucci Music Library, you may be interested in reading Lamperti.

He's there too. Just click here. It will take you to a page where you can download Giovanni Battista Lamperti's The Technics of Bel Canto which was first published in 1905. Curiously, like the two great Garcia's, there were also two Lamperti's.  Francesco's son Giovanni Battista had his teachings immortalized in Vocal Wisdom: Maxims of Giovanni Battista Lamperti, after his student, William E. Brown, published his lesson notes in 1931 (sorry...I don't have a download link for this book because it is still in print! However, you can easily, and inexpensively, find a copy at Amazon). 

If the influence of Vocal Wisdom has been greater than The Technics of Bel Canto, it may have everything to do with the 'voice' of the former, which is more accessible - more right-brained - than the logical and theoretical latter. 

Vocal Wisdom appeals to the senses, particularly the sense of hearing.  This has everything to do with empiricism.

The drawing is from a newspaper clipping I ran across a few years ago.  I can't decide if Lamperti is about to laugh with—or scold—the viewer. Whatever he was thinking, it's an intense expression.