178 REPORTS ON THE STATE OF SCIENCE.—1917. 
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 flotation 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, prac- 
tical 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 appre- 
ciate 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 tempera- 
ture 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 under- 
standing 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 
bo due to insufficient 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 
ié in too limited a supply of air; this will lead to the suggestion that the 
