244 Master Minds of Modern Science 



before Kew reports " visibility good " it is necessary for 

 the observer on the roof to see clearly a distance of twelve 

 and a half miles. A visibility of one and a quarter miles 

 goes down in the records as mist or haze. 



The atmospheric pollution in fog is measured, and so is 

 the amount of dirt in rain. 



The dirt in fog-laden air is measured by sucking the air 

 into an instrument, inside which it passes through a piece 

 of filter-paper, leaving tell-tale spots of dirt, which are 

 then examined under the microscope. 



Finally, wind is measured by a weather-vane which 

 writes down its own messages. Both the direction and 

 force of the wind are automatically recorded, for as the 

 wind blows it moves a thin metal arm at the end of which 

 is an inked pen-nib. This nib traces a graph line on a roll 

 of measured paper, which is renewed daily. 



Every day observers scattered over Britain are record- 

 ing the weather with the aid of these instruments. A 

 simple code has been devised for use in the transmission 

 of weather reports to London. Thus two capital R's 

 mean that it has rained all day. Letter o means an over- 

 cast sky, while p denotes passing showers, b means blue 

 sky, not more than one-quarter covered by clouds. But 

 a combination of letters more frequently used in the North 

 is c.d.m. — meaning generally cloudy, drizzle, and mist. 



It is all very simple to read about, but years of research 

 and experiment have been needed to bring the Meteoro- 

 logical Office to its present pitch of efficiency. Always 

 the experts are seeking fresh knowledge, for there are still 

 many things to be discovered about weather. Granted 

 the opportunity of studying the weather conditions at the 

 Poles, weather experts may presently be able to provide 

 long-range forecasts of summers and winters, which will 

 be of immense assistance to agriculturists all over the 

 world. 



