130 Dr. C. Chree. Observations on Atmospheric 



but it is rather apparent than real. For if, instead often, we adopt 

 eleven miles an hour as limiting value for the velocity, we get in that 

 instance two equal groups with the following results : 



Group. Mean velocity. Mean potential. 



1st 19-6 153 



2nd 6-8 175 



Higher potential is here associated with lower velocity, and, as the 

 groups are equal, the result is presumably a fairer representation of 

 the facts than that afforded by Table XXII. 



Whilst the association of high potential with low wind velocity in 

 the forenoon seems thus conspicuous, there is in the afternoon no 

 certain evidence of any such connexion. Thus, in Table XVII, 

 higher potential is associated as often with higher as with lower 

 velocity ; and in Table XXII, whilst higher potential is associated 

 with lower velocity in three sub- cases out of four, the differences 

 between the mean potentials for the first and second groups are 

 small. In series III observations the difference is also very uncertain. 

 If, for instance, we divide these observations into two equal groups, 

 by taking 15 as separating value for the velocity, we obtain for each 

 group identically the same mean voltage, 103, though the mean 

 velocities for the two groups are respectively 18'7 and 8*1. 



In Table XXII the figures obtained by combining all four series of 

 observations, afford an excellent example of what may happen when 

 results, from all seasons of the year, are treated promiscuously. The 

 individual series, as we have seen, show no clear association of high 

 potential with low velocity in the afternoon observations, but, when 

 the four series are combined, such an association seems conspicuous. 

 The phenomenon, in reality, is mainly due to the comparatively large 

 number of instances in which the velocity happened to be high 

 during the season when the potential was at its minimum. 



General Summary of bearing of Results on Theory. 



29. A comparatively small number of observations may be suffi- 

 cient to disclose defects in an existing physical theory, and yet be 

 inadequate to warrant the promulgation of a positive opinion as to 

 the true theory. This is the most satisfactory point of view from 

 which to regard the facts presented here. They are, in my opinion, 

 sufficient to show the incompleteness of any theory which assumes 

 simultaneous values of potential and any single meteorological element 

 to be so intimately connected that the value of the one can be 

 deduced, as a rule, from that of the other without taking into 

 account other important influences. On the other hand, they are 

 not sufficiently varied to justify the conclusion that the connexions 



