18 Radium Emanation in Lower Regions of the Atmosphere. 



the weather data in the tables are, however, taken from the 

 records given in the Meteorological Office's publication 

 entitled ' Observations at Stations of the second order and 

 at Anemograph Stations.' The Cambridge station is at 

 the University Botanic Garden, situate about half a mile 

 from the laboratory and at the same level. Readings are 

 taken there twice a day — 9 a.m. and 9 P.M. The maximum 

 temperature occurs during the afternoon, so the maximum 

 thermometer is read at 9 p.m. and entered to the day. The 

 minimum temperature usually occurs in the early morning. 

 It is read at 9 a.m. and entered to the day. The humidity is 

 obtained from the ordinary wet and dry bulb thermometers. 

 The rain-gauge is read at 9 A.M. each day, and since most of 

 the 24 hours since the last reading occurs in the previous 

 day, it is entered to that day. The sunshine is measured by 

 a Campbell-Stokes recorder. The wind force is given on the 

 Beaufort sc;ile. It is estimated by the observer using the 

 indications given in the ' Meteorological Observer's Handbook.' 

 The numbers 0, 1,2, 3, 4, 5, 6, 7, 8 on the Beaufort scale cor- 

 respond approximately to wind velocities of 0, 2, 5, 10, 15, 

 21, 27, 35, and 42 miles per hour. A number affixed to a 

 weather phenomenon under the column Weather Remarks 

 indicates the intensity of that phenomenon, thus, Snow° = 

 light fall of snow, Rain 2 = heavy fall of rain. Also a = A.M., 

 p = P.M. The amount of emanation is given as the leak pro- 

 duced in my testing vessel measured in cms. per minute on 

 my electrometer-scale. 



From the figures in these tables the curves (Plate I.) were 

 plotted. Owing to the stoppage of work at the week-end 

 it was unfortunately impossible to obtain a continuous ema- 

 nation-curve ; but in some cases the curves are linked up 

 according to the knowledge gained from the determined 

 portions. 



Analysis of the Curves. 



(1) Let us now consider the emanation-curve in conjunction 

 with the barometer-curve. Table VI. opposite gives the results. 

 The letter D after a date means a decided change in the 

 amount of emanation ; and the letter R or S means that rain 

 or snow accompanied the barometric change. 



From this table we see that, on the whole, a rise in the 

 barometer is accompanied by an increase of the amount of 

 emanation, a fall of the barometer is accompanied by a decrease 

 in the amount of emanation, while with the barometer fairly 

 steadv the issue is doubtful. 



