PRECIPITATION 23 



In detail, of course, the order of study must depend upon 

 the general arrangement of the school course, but at an early 

 stage allusion may be made to the main facts connected with the 

 structure of Britain, as illustrating on a larger scale the facts 

 observed locally. Thus, one would point out that all the great 

 backbone of mountains which runs down through Great Britain 

 presents a rainy side to the ocean, and a less rainy side to the 

 east. If the western side be the wetter side, however, there 

 the streams will be most frequent, there also the mountain sides 

 will be most deeply carved out by the water, while the wearing 

 action of the water will be less on the other side. 



The next point is of course to indicate in some way the difference 

 between the steep rocky Atlantic sea-board and the more fertile, 

 gently-sloping eastern slope, the facts being considered in relation 

 to rainfall and erosion, and their geographical significance merely 

 suggested. 



2. MEASUREMENTS OF RAINFALL. To give exactness to 

 meteorological observations of the type suggested above it will, 

 however, be necessary that the members of the class should 

 actually measure the diurnal variations of one or other of the 

 elements for themselves. In the first place, at least, there is much 

 to be said for allowing them to measure the rainfall by means of 

 a rain-gauge, and this for several reasons. If the barometer be 

 chosen, we have to face the fact that the small daily variations, 

 except during the passage of considerable cyclones, are not easy 

 to interpret. For all ordinary purposes, indeed, the terms rising 

 or falling, high or low, may be said to suffice. Not till the stage 

 when meteorological charts can be used is more required. The 

 case is similar with the thermometer. Except when the varia- 

 tions occur round the freezing point, where they have consider- 

 able economic importance, variations of a degree or two, up or 

 down, do not directly affect daily life, and observations must 

 therefore be kept over a considerable period before the observer 

 can accumulate a sufficient basis of experience to interpret them, 

 or find in them any great degree of interest. Although, therefore, 

 it is a good plan even from an early stage to add occasionally 

 to notes of the weather a reading of barometer and thermometer, 



