It is impossible in the short space of a 80 single article to set out the details of a systematic course of training sufficient to fit the housewife to use her judgment wisely in circumstances which require a knowledge of the principles of the fundamental physical sciences. The most that we can attempt is to give a few examples which illustrate the application of the principles of physics and chemistry. Our purpose in doing so is to suggest illustrations which appeal to every householder, and may create a desire for fuller knowledge rather than to supply a course of instruction. What we aim at is not to provide the equipment of scientific training, but to show that the scientific habit of mind will find opportunities for useful employment in many of the most ordinary affairs of life. The problems that present themselves in the course of experience are sometimes difficult and intricate; patience and careful observation as well as knowledge are required for their solution. Sometimes this solution is beyond the immediate resources of those concerned, and it is a part of scientific training to recognise when this is the case, so that effort and money may not be wasted in endeavours which are foredoomed to failure. We may cite a case in point where an extra bell was desired in a system of electric bells in a flat at a time when electric installations in private houses were somewhat rare, and workmen with any knowledge beyond that necessary for carrying out instructions were not easily found. To the confusion of the tenant, the introduction of this extra bell caused all the bells in the flat to strike 81 work. A mathematical lecturer living in the same building was consulted, and opined that the battery of two somewhat small-looking cells was insufficient, so he obtained and added a larger cell, but the bells were obdurate and did not resume work. A lady with knowledge of physics examined the installations and discovered that the wire connections as altered were entirely wrong and did not connect the bells to the battery. A plan of the correct connections was shown to the workman, who a few days later reported that now all the bells rang at once, and he had had to disconnect the battery! He produced a sketch of the connections he had made, and on his error being pointed out he was able to rectify it, and the bells answered to touch without the use of the extra cell. Generally speaking, a failure on the part of electric bells is corrected by filling up the cells which compose the battery with water, an operation which any one may undertake.
It is not safe, however, for an inexperienced person to interfere with electric light fittings further than to remove a worn-out lamp and place a new one in the socket, and even this operation may be attended with disaster. A young friend of ours who was taking part in some private theatricals obtained the loan of a row of electric footlights. It did not occur to any one concerned to ask the voltage of the lamps or of the current to which they were to be applied. When the footlights were turned up they blazed for a brief period, and then every light in the house went 82 out! Electrical science for the housewife has been resolved into a knowledge of electric terms and of a few practical rules useful and interesting in themselves, but not immediately suitable for our purpose of showing how scientific study may aid the housewife in her daily routine.
PHYSICAL SCIENCE IN THE HOUSEHOLD
We may for this purpose examine some of the laws of common physical and chemical phenomena, neglect of which has resulted in much needless discomfort in daily life, and even more serious consequences. For instance, the laws of expansion of gases and liquids with heat, and their subsequent behaviour, are phenomena that are often imperfectly realised. There is probably no person who is unacquainted with the law of gravitation, but there are many persons who accept literally the statements that smoke rises and that balloons ascend. A clear understanding of what actually takes place when gases and material masses appear to move in opposition to the law of gravitation is essential to any scheme for warming and ventilating the house.
A very simple experiment will serve to reconcile the apparent contradiction of the universal law by the observed fact. Suppose we have two fluids, oil and water, of which oil is, bulk for bulk, lighter than water. If the oil be poured into a glass beaker, it will be seen to rest at the bottom of the beaker; if water be now poured into the same 83 beaker the water will go to the bottom of the beaker and will displace the oil and lift it up so that the oil will float on the water; the oil may be lifted to any height we please if sufficient water be poured in to lift it to that height. If a single drop of oil be introduced into the water by means of a pipette and be liberated at the bottom of the beaker the water will close in under it, and lift it up to the surface. In both cases the oil “rises” through the water. Oil, however, has no tendency to “rise” by itself, and in this case it lay motionless until it was lifted by the heavier fluid. We may use colloquial language when describing phenomena if we bear in mind what is really taking place.
A balloon “rising” through the air is exactly analogous to the drop of oil in the water. The balloon is, bulk for bulk, lighter than air; the air therefore closes in under it and lifts it just as the water lifted the bubble of oil.
EFFECTS OF CHANGES OF TEMPERATURE ON AIR
Let us apply this to air. Air when warmed expands, and therefore warm air is, bulk for bulk, lighter than cold air. Warm air behaves in the presence of cold air as the balloon: it is displaced and lifted by the cold air, the result being an ascending stream of warm air, which is called a convection current.
The movement of ascending smoke is essentially 84 the same as that of the warmed air. Smoke is warm air made visible by the particles of soot with which it is laden. The particles of soot would fall to the ground except that they are carried upwards in the stream of warm air. Dr. W. N. Shaw has called attention to the importance of these phenomena in his book on “Air Currents and the Laws of Ventilation,” in the Cambridge Series of Physical Text-books. He there says: “The dominant physical law in the ventilated space is the law of convection. It is at once the condition of success and the cause of most failures. Without convection, ventilation would be impossible; in consequence of convection, nearly all schemes of ventilation fail.
“The law of convection is the law according to which warmed air rises and cooled air sinks in the surrounding air. Its applications are truly ubiquitous. Every surface, e.g. a warm wall, or a person warmer than the air in the immediate neighbourhood, causes an upward current; every surface colder than the air in contact with it causes a downward current.