24 Mr. J. Satterly on the Amount of Radium 



so that it had not much time for picking up emanation from 

 the land over which it passed. 



Carve (4) of Map 1 gives the trajectory for the air arriving 

 at Cambridge on June 16 at 6 p.m. It was traced back to 

 June 13, when it was found to come from a northern region 

 of gentle airs between an Icelandic high pressure region and 

 a Norwegian low pressure region. The air leisurely pursued 

 its southerly course to Cambridge, being over the sea all the 

 time except for the last 50 miles. Its emanation-content 

 would naturally be low. 



Curves (1) and (2) of Map 2 give the trajectories for the 

 air arriving at Cambridge on June 2, 6 p.m., and June 3, 

 t) P.M. The air had travelled at a great pace across the 

 Northern Atlantic between a cyclone in the Icelandic region 

 and an anticylone to the south of its course. It hung about 

 ior a short time in a quiescent region around the Shetlands, 

 and finally travelled southwards at a great pace behind a 

 very long V-shaped depression which was travelling east- 

 wards to Denmark, and which gave us heavy rains on the 

 evening of June 1 and the morning of June 2. 



Curve (3) of Map 2 gives the trajectory of the air arriving 

 at Cambridge on May 25, 6 P.M. The air was traced back 

 to the quiet interior of an anticyclone which had hung about 

 over the continent since May 17. No doubt the interior of 

 this anticyclone was occupied by air which had just descended 

 from the upper regions so that the surface trajectory could 

 not be traced beyond the 24th. Tbe air reaching Cambridge 

 had thus made little contact with land, thus explaining its 

 low emanation content. 



All the paths of the trajectories mentioned above agree 

 very well with the small amount of emanation the air in 

 them carried. 



The trajectories for the air giving high results do not give 

 such good agreement. This is no doubt partly due to the 

 fact that high results occur in fine weather and the winds 

 in fine weather are light and variable. 



Trajectories of the surface air-currents arriving at Cambridge 

 when a high value of the emanation content ivas obtained 

 (Maps 3, 4, 5). 



Curve (1) of Map ,3 gives the trajectory of the air arriving 

 at Cambridge on March 5, 7 a.m. There had been a number 

 of sporadic cyclones in N.W.Europe for the past 4 days, 

 and the winds had been light. The air. was .traced .back 



