1907] The Weather 49 



*'liighs" originate mostly in the Northwest, it brings with it the 

 cold air of the upper regions, although modified in its tempera- 

 ture by descent. From years of experience the forecaster, 

 having his constructed weather chart before him, showing the 

 conditions at an absolute instant, can make a pretty accurate 

 estimate what the atmospheric movements are going to be for 

 the next 24 or 36 hours, that is, he gives us our daih' probabi- 

 lities. It may be mentioned that our Canadian Meteorological 

 Service in accuracy of prediction is second to none other. 



If we know what time a train leaves Calgary or Edmonton 

 across the continent we have a pretty fair notion (barring bliz- 

 zards) when it is going to arrive at Ottawa, and so the forecast- 

 ers having been advised from many sources of the departure of 

 the atmospheric cttrrents knows pretty well when they will ar- 

 rive here and how they are going to behave. We must bear in 

 mind that electricit_v "travels faster than weather. If the tele- 

 graph wires were all' cut and the meteorologist were dependent 

 wholly on his own local observations, our daily "probabilities" 

 would have little value. We see then that the meteorologist 

 simplv tells us from what has begun to happen what is going to 

 happen. 



But why does it happen, why has the air persisted to pile 

 itself up sk3'-high so to speak in the Northwest, and mam- other 

 whys ? 



It is not known, is the answer in brief. But in saying so, 

 it must not be imagined that the problem is not being attacked, 

 and vigorously attacked. The explanation of the beginning of 

 the circulation is very simple. Our great furnace, the Sun, ob- 

 livious of the price of coal, is pouring his heat into space and 

 our earth intercepts a A-ery, very small part of it. Where the 

 rays fall vertically or nearly so, more heat is received than where 

 they fall slantingly ; compare the melting of snow on a roof facing 

 the sun straight, with one facing sideways, that's exactly the 

 effect in the equatorial and temperate regions. The earth and 

 air in the former become in consequence our terrestrial furnace, 

 receiving the most heat. The heated air rises, and necessarily 

 air to the south and north of the equator flows along the surface 

 to take the place of the ascending air. The circulation of the 

 air has begun. The rotation of the earth modifies the currents 

 in direction and otherwise. Without pursuing the circulation 

 of the air thus started any further, being outside the scope of 

 the present note, it may be pointed out that the earth revolves 

 on its axis from year to year in the same time and its journeys 

 around the sun follow the same old trail during our life-time, 

 the mountains and vallevs on the earth or other topographic 



