An interesting and important principle, explained on page 23 of Part I, and again on page no of Part III, is Conservatism. This principle has been established by countless experiments, but it is not one that the housekeeper can well investigate. It is, however, one she must continually bear in mind. Matter and energy can never be created or destroyed; both may be transformed, and may therefore appear in many different ways. The voltaic cell is a simple device for transforming chemical energy into electrical force. The chemical affinity of two substances causes them to unite under the right conditions. This union results in the liberation of energy, which may appear as heat, light, or electricity. When coal and oxygen unite, we get both heat and light as a result. Chemical union usually produces heat.

The energy of our bodies we get solely from the food we absorb. We should eat such foods as best give us the needed energy, and we should learn to expend this energy wisely, as we have but a limited amount of it. One student wisely comments upon this, as follows:

"In the economic plan of housekeeping, it would be well if each one would endeavor to realize that she is a part of the machinery of the household, and that to be continually on the move is as disastrous to the equilibrium of the home as it is to rust, as it were, for want of use. A given amount of rest each day is a true part of economy. Then, too, in the daily regime, there are ways and ways of doing things. Always choose the easiest, if it con flicts not with the quality of the work done. For example, do not stand while paring potatoes, apples, etc. It is just as easy to do this work sitting, and you can then get some rest at the same time. Don't worry - to worry is a very extravagant thing, for it uses up valuable force, and does no good at all."