Page:Proceedings of the Royal Society of London Vol 60.djvu/145

130 but it is rather apparent than real. For if, instead of ten, we adopt eleven miles an hour as limiting value for the velocity, we get in that instance two equal groups with the following results :— 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 8T.

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.

§ 29. A comparatively small number of observations may be sufficient 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