114 Dr. C. Chree, Observations on Atmospheric 



though doubtless in very variable degrees at different seasons. Solar 

 radiation occurring after an observation is taken, clearly cannot 

 affect it. Thus the data got out as to the amount of bright sunshine 

 recorded prior to the observations must, I think, bear fairly directly 

 011 Elster and Geitel's theory. If it be true, the potential gradient 

 must, I think, fall conspicuously as the number of hours of previous 

 sunshine increases. 



19. An objection of a different kind is the proximity of the Kew 

 Observatory to London. This objection has already been urged 

 against Greenwich by investigators* whose theories do not harmonise 

 with the results obtained there. A weekly period exists, they say, 

 in the Greenwich electrograph curves, and this, they assume, can 

 arise only from a weekly fluctuation in the amount of smoke, due to 

 our insular habits of keeping Sunday. If, for a moment, we suppose 

 the phenomenon and explanation both true a pretty large assump- 

 tion there seems a wide step to the conclusion that results so 

 affected are useless. I do not myself see that they need lead to 

 erroneous conclusions, unless one is dealing with a cycle whose period 

 is seven days, or a multiple thereof, which a lunation, for instance, 

 is not. 



In the present instance I would point out that the prevailing winds 

 during each one of the series of observations were from directions 

 included between N.N.W. and S., and that as Kew Observatory is 

 some miles to the west of London, while the manufacturing 

 districts are mainly in the east, it is difficult to see how London smoke 

 could affect the results. The Observatory, I should add, is situated 

 in a large open park to the immediate west of the extensive Kew 

 Gardens. 



Even if the prevailing winds had been easterly, I question whether 

 smoke would have exerted an appreciable influence. The analysis 

 above mentioned of the electrograph results for 1880, by the late 

 Mr. Whipple, seems to show that if any relation existed then between 

 electric potential and wind direction, it varied with the season of the 

 year; this would hardly have occurred if smoke present in east 

 winds had an appreciable effect. 



Tables of Results. 



20. In discussing the observations, I have decided to commence 

 v by incorporating the actual details in a series of tables. This 

 will enable any one to judge for himself whether the conclusions 

 finally arrived at are in accordance with the facts. The first eight 

 tables give full particulars of the results. The arrangement is not 



* See pp. 4243 of offprint of paper by Ekholm and Arrhenius in ' Bihang till 

 i. Svenska Vet.- At ad. Handlingar,' Band 19, Afd. 1, No. 8, Stockholm, 1894. 



