The mechanics of fluid friction and the transfer of heat are not understood to this day. Its history records a variety of approaches to an understanding that spans over 230 years. Clearly, the correct rationale is elusive. The use of pipes, ducts, and channels is not being hampered by the lack of this basic knowledge, as conduit systems are everywhere. What is being hampered that the book addresses are efficient design and predictability of performance. When the author discovered the principles of equivalence, similar flow, and the similarity of flow, the subject matter exploded into clears-cut paths of logic ripe for development and new discoveries. The resultant discovery of the natural friction factor leads to the natural reference circuit and the new smooth and rough-pipe laws. This in turn leads to the new combined-flow reference law. The momentum continues to discovering the mixed boundary layer, the kinematic thermal conductivity, a definitive explanation of viscosity, the real friction velocity, and the friction Reynolds' number. A new perception of fluid friction evolves from the study. The mechanics of fluid friction and the transfer of heat are thus synthesized.