WEATHER AND CLIMATE 9 



of this kind, and by drawing frequent attention to the barometer at 

 times when it is changing rapidly, drive home the fact that though 

 the changes of the barometer are often associated with changes 

 in temperature, humidity, and the direction or force of the wind, 

 which we can perceive with our senses, yet we have no sense per- 

 ception of that change in pressure to which the barometer responds. 



In the same way point out that although our senses register for 

 us changes of temperature yet their indications are very inexact. 

 It is easy to bring this out by questions the same day will be 

 regarded as warm by some children and cold by others, the sensa- 

 tions even of the same person altering with hunger and fatigue. To 

 further emphasise the point insist upon all the children performing 

 for themselves the old experiment with water of different tempera- 

 tures. One hand should be plunged into cold water, the other into 

 hot, and after a few minutes both hands should be plunged into 

 warm water. The one hand will receive the sensation of warmth 

 and the other of cold. Each child should be made to do this for 

 itself, and by judicious questions the meaning of what the psycho- 

 logist calls the subjectivity of sensations should be clearly brought 

 out. It is obvious then that if we had no instruments, if we were 

 shut up exclusively within the limits of our individual sensations, 

 the scientific study of our surroundings would be impossible. 

 Before any attempt is made to explain the thermometer and the 

 barometer, their value should be made clear in this way. 



We may next make practical use of these instruments, and 

 especially of the thermometer, before proceeding to explain them. 

 The explanation will come much better at a later stage when we 

 have used them constantly and realised their usefulness. On the 

 school excursions, then, let us take an aneroid barometer and a 

 thermometer. From our observations of the first we learn that 

 while it does not change (during short periods of time that is) on 

 the level, it begins to go down when we climb a hill, or rises if we 

 descend. At this stage pictures and stories of Pascal on the Puy de 

 Dome and de Saussure on Mt. Blanc will be appropriate. In 

 Whymper's Guide to Chamonix there is an interesting reproduction 

 of a picture showing one of de Saussure' s excursions on the 

 Mt. Blanc range, with the huge cavalcade of porters carrying 

 the impedimenta. If this picture can be shown to the class, and 



