an Elster and Geitel Electrical Dissipation Apparatus. 481 



§ 5. The large size of a and q' is due not to the existence 

 of any considerable number of exceptionally high individual 

 values of g, but to a persistent tendency of a_ to be sub- 

 stantial^ larger than a + . This is readily seen by reference 

 to Table II. The first line shows the total number of occasions 

 when q lay within the limits specified, the second the 

 percentages which these form of the whole 411 individual 

 observations. 



Table II. 



• 



< 1. 



1 to 2. 



2 to 3. 



>3 



Number of occasions 



42 



10 



291 

 71 



61 

 15 



17 



4 



1 





Of 



the 42 days when 

 id in December 



exceeded a_ no less than 15 

 occurred ueceniDer or January. It is a curious fact, 

 which may be worth noting, that low values of q seemed to 

 have a tendency to occur on successive days. On one 

 occasion values less than unity happened on 4, and on three 

 occasions on 2 successive days. 



Of the 17 days when q exceeded 3 only two occurred in 

 the summer months May to August. 



The largest value of q actually recorded was 8'$ — in 

 November 1907, — but in this and one or two other cases 

 where q was exceptionally high or low, some doubt may 

 reasonably be felt as to the accuracy of the result. 



At Kew, a large value of q means usually a very small 

 value of a + , a small value of q a small value of a_. Now 

 individual observations cannot claim any very high pre- 

 cision, and when dissipation is small the loss due to defective 

 insulation is apt to represent rather a high fraction of the 

 total, so that the probable error in a low value of a + or a_ is 

 very considerable. 



§ 6. Table I. shows a well-marked annual variation in 

 dissipation, though obviously a good many more years' 

 observations would be required to give smooth results, 

 Taking the mean of a + and a_, we have the maximum 

 dissipation in June and July and the minimum in January, 

 February, and March. The annual variation is the opposite 

 of that in P, but the difference between summer and winter 

 is less pronounced. It should, however, be remembered that 



Phil. Mag. S. 6. Vol. 20. No. 117. Sept. 1910. 2 K 



