The division into lessons is necessarily, to some ex tent, arbitrary. The lessons may be found too long or too short, according to the time which the school may be able to allow. An intelligent instructor will easily combine them or subdivide them as occasion may require. I am indebted to Messrs. Fairbanks Co. For the design for a small testing-machine, Fig. 8, and to my colleague, Professor William Stratford, for the micro-photograph of a section of the wood of Pinus Sylvestris, Fig. 6.