The arrangement of this book is such that it may be used equally well by science teachers in the regular secondary and technical schools and by science teachers in vocational schools. When used in connection with a year's course in industrial science in the technical, industrial, or manual training courses of regular secondary schools, it will aid in correlating the principles of science with shop observation and experience.

The method of presenting the subject of industrial science in a vocational school should be different from the method used in the regular high school, since there is a wide difference both in the aims of the courses and in the types of pupils. In the vocational school it is well to consider first the practices PC the trades and industries as based on practical shop experience and laboratory work, and from them to draw out the principles of science involved.

To illustrate: In considering the properties of matter in a metal like copper, present first the uses of copper; it is used, for instance, in the manufacture of sheet metal and wire. To be used as sheet metal, it must be capable of "being worked," that is, hammered into sheets - it must be malleable. The same reasoning applies to its use as wire; it must be capable of being "drawn out" - it must be ductile. As Walter Dill Scott says in "Influencing Men in Business". "Water is not adequately described by stating that it is composed of two parts of hydrogen to one of oxygen. The important thing about water is the uses which may be made of it."

This method will be found to be far more effective in teaching vocational school pupils than that of presenting the principle first and the illustrative practice afterwards.

Chemistry explains the changes that take place in a substance when its identity is destroyed. When iron, for example, is exposed to damp air, it becomes covered with a reddish brown substance called rust. This rust is due to a combination of the oxygen and moisture of the air with the iron. Copper or brass when exposed in this way becomes greenish in color from the same cause. The science of chemistry makes clear why such changes as these take place.

Other sciences explain the why and wherefore of other classes of phenomena or physical changes. Thus, botany treats of the growth and changes in plants. Bacteriology explains how changes in substances are caused by germs. An example of such a change is the rotting of wood. Geology treats of the structure of the earth, especially of rocks. Hygiene explains the principles underlying the care of our bodies. It is desirable to understand the principles of science as they relate to the different trades, so that we may have an intelligent knowledge of the processes and changes whereby raw substances or materials taken out of the ground are transformed into useful and beautiful things.