502 REPORTS ON THE STATE OF SCIENCE, ETC. 



answered by their own experiments, as, for example, if a loaded wheelbarrow 

 has to be raised to a certain height, is it better to have a short steep slope or a 

 longer and more gradual one ? 



A study of iiotation may very naturally develop from such a course as this. 

 Why do some bodies float on water and others sink ? Why do some bodies float 

 higher in the water than others ? Why do bodies float higher in salt than in 

 fresh water ? Is any of the weight of a body that sinks supported by the water ? 

 These will be among the questions asked and answered by experiments. They 

 will lead up to an understanding of relative density, and of the Principle of 

 Archimedes. When the principle has been grasped, practical applications should 

 be worked out, calculations being made and the results tested by experience. 

 The weight of cargo which it is safe for a boat to carry, or the size of a cork life-belt 

 necessary to support a person, are problems which, even if toy boats and tin 

 soldiers are used, help the children both to grasp the practical value of the knowledge 

 gained and also to appreciate the need for accuracy. 



The fact that ice floats on water may well lead on here to investigations into 



(1) changes of density and volume produced in substances by change of temperature, 



(2) change of state, together with the influence of pressure upon it, (3) some 

 methods of transmission of heat, and (4) means of measuring temperature and 

 heat. Plotting curves of temperature for the heating of water over a flame till 

 it boils, and for the cooling of melted paraffin wax, will give the idea of latent 

 heat. The heating of a definite weight of water by the immersion in it of given 

 weights of different substances at the same temperature will give the idea of 

 specific heat, and these conceptions may now be developed in their geographical 

 and practical bearings. Discussions as to the methods of heating buildings and 

 obtaining hot-water supply, the working of a cooking-box, &c., will naturally arise 

 during this course. 



Flotation in the air will lead on to an estimate of the weight of air by the 

 method of driving it from a flask by boiling water, and this to the idea of pressure 

 of the air. The experiments of Torricelli and the work of Boyle on the ' Spring 

 of the Air ' may here be considered in historical order, and different forms of 

 barometer, pumps, siphons, and so forth may be studied. A consideration of 

 winds and of weather charts will here, again, form a link with geography. 



At this stage a continuous piece of investigation necessitating the framing 

 of tentative inferences or hypotheses, and the testing of these by further experi- 

 ment, becomes increasingly possible, and helps greatly to deepen the understanding 

 of the method of development of scientific knowledge. Many chemical problems 

 form excellent material. Amongst others, the problem as to what we understand 

 by burning arises very naturally out of work already done. 



Preliminary questioning as to what burning is will usually lead to the sug- 

 gestion that it consists in a partial or complete disappearance or ' consuming ' 

 of the object burned. Experiments with match, candle, &c., seem to confirm 

 this ; the weighing of magnesium before and after burning discredits it, and 

 demands, therefore, further investigation. The fact that some member of the 

 class has probably observed the magnesium glow more brightly on the lid of 

 the crucible being removed, suggests that air influences burning and may cause 

 the increase of weight. The question then arises, does the air then diminish ? 

 Burning magnesium in a crucible floating on water under a bell-glass shows that 

 it does. Therefore the magnesium calx must represent magnesium and air. Why 

 has the whole air not disappeared ? Suggestions that this may be due to in- 

 sufficient magnesium being burned must be put to the test, and the properties of 

 the gas left compared with the properties of the air to begin with. Details of 

 Priestley's and Lavoisier's experiments with the red calx of mercury may now be 

 given for comparison, and the red calx heated by the pupils. Other substances 

 may then be dealt with, e.g., carbon. Carbon disappears. Is a new gas formed ? 

 Collection of the air above the heated carbon and testing of this, together with 

 ordinary air, by a match, by litmus, and by lime-water, reveal the fact that a new 

 gas has appeared. Probably someone, in the effort to collect the gas, has failed to 

 get the carbon to disappear, owing to heating it in too limited a supply of air ; this 

 will lead to the suggestion that the carbon also unites with oxygen. Heating small 

 quantities in oxygen and nitrogen will reveal the fact that no new gas is formed 

 in the latter case, while it is formed abundantly in the former. A further confirmatory 

 experiment may be made by the burning of magnesium in carbon dioxide. 



