22 Mr. J. Satterly on the Amount of Radium 



as definite in their structure as cyclones. The only V-shaped 

 depression experienced gave plenty of rain, strong winds, and 

 a decided decrease in emanation content, 



(5) The effect of fine weather was analysed in a similar way 

 to the above. In 1 case there was no effect on the amount 

 of emanation, in 5 cases a decrease of emanation, and in 15 

 cases an increase. There were also 3 cases of increase on 

 dull days (trace of rain only), and 12 cases of decrease on 

 days which were not fine (these were chiefly rainy days). 



(6) The path of the wind. One would expect that if the 

 air that was carried over Cambridge had travelled for a long- 

 time over land, it would have a large emanation content; 

 while if it had travelled over the sea or very rapidly over 

 the land, it would have a small emanation content. It is 

 not an easy matter to work out the actual path of the surface 

 wind. Shaw and Lempfert * have worked it out for certain 

 selected cyclones, anticyclones, and V-shaped depressions, 

 and have traced the life-history of the currents in great detail 

 in their interesting paper. The path of the air has, however, 

 to be traced very warily for the conditions are often very 

 indefinite. Dr. Shaw w as kind enough to let me go up to 

 the Meteorological Office and work out the paths of the winds 

 from the Working Charts kept there. These working charts 

 are synchronous maps giving the distribution of the meteoro- 

 logical elements at specified instants. They are got out 

 three times a day, 7 a.m., 1 p.m., and 6 p.m., and are used for 

 the weather forecasts j\ On these charts the isobars are 

 drawn for every -^ in. of pressure and the wind indicated by 

 arrows, the barbs and feathers showing the strength on the 

 Beaufort scale, or by a simple calculation in miles per hour. 



The method adopted by me in drawing the surface trajec- 

 tories is that given by Shaw and Lempfert in their paper. 

 They say: " If we take the synoptic chart for any epoch we 

 know to a moderate degree of approximation the speed and 

 direction of the wind. The wind observations give us the 

 information for certain points, and the known relation between 

 wind and barometric gradient helps us to interpolate for 

 points on the chart for which no actual wind observations 

 exist. The continuous records of anemographs show in detail 

 what the nature of the changes were for particular localities. 



" A knowledge of the direction of the wind at any point 



* See Shaw and Lempfert, ' The Life History of Surface Air-Currents. 

 A Study of the Surface Trajectories of Moving- Air.' Published "by the 

 authority of the Meteorological Committee, 1906. 



f An interesting elementary account of the Construction and Reading 

 of Weather Maps is given by E. Gold in the ' School "World ' of July 

 Augustj and September, 1909/ 



