[cLiNE] RADIATION AT THE SURFACE OF THE EARTH 1-41 



With the apparatus set up in the manner just described sets of 

 readings were taken during the afternoons of March 15, 22 and 26, 1909. 

 The results of these measurements are recorded in Tables XII, XIII 

 and XIV, and curves illustrating them are shewn in Figs. X, XI and 

 XII. 



The readings for the three afternoons, it will be seen, approximated 

 to 11 ions per cc. per second. 



By comparing the three curves it will be seen that although 

 the readings were not uniformly regular still no periodic daily 

 variation was brought into evidence. On March 28 and 29 and 

 again on April 4 and 5, 1909, readings were again taken with this 

 apparatus continuously over periods of twenty-four hours. The 

 readings taken during these observation periods are given in Tables 

 XV and XVI and the corresponding curves are shewn in Figs. XIII 

 and XIV. These readings it will be seen are far from being so uniform 

 as those of the earlier observations. The variations from the mean it 

 will be seen are very considerable, and are attributable in the judg- 

 ment of the writer, to the lack of sensitiveness in the instrument and 

 the consequent difficulty in taking the readings, rather than to any 

 variations in external influences. 



In Fig. XIII the barometric curve is drawn for the corresponding 

 twenty-four hour period. From an inspection of the two curves there 

 does not appear to be any connection between the changes in conduc- 

 tivity and the changes in atmospheric pressure as indicated by the 

 barometric readings. 



In order to see whether a combination of the curves shewn in 

 Figs. XIII and XIV would give any indication of a pronounced maxi- 

 mum and minimum conductivity the two curves were compounded by 

 taking the mean of the readings for the same time of the day. The 

 individual curves are shewn overlapping in the upper portion of Fig. 

 XV, and the compound curve is shewn at the bottom of the same 

 figure. From the figure, however, it is impossible to draw the con- 

 clusion that any maximum or minimum conductivity was associated 

 with any particular hours of the day. 



While the lack of sensibility in the measuring instruments pre- 

 vented these later observations from leading to as satisfactory con- 

 clusions as might be desirable, still they agree with the earlier ones in 

 failing to point to any variation of a regular diurnal character, and in 

 this they seem to show that the conditions at Toronto are some- 

 what different from those which prevail in a number of other localities 

 where similar observations have been made. 



The writer had hoped to continue the investigation out in the open 

 country with the electroscope arranged as adjusted for maximum 



