320 TRANSACTIONS OF SECTION A. 
a long series of observations reduced on a uniform plan. The best I know 
is in Newcomb’s ‘ Astronomical Constants.’ He gives there the material for 
the earth arranged in groups of a few years at a time. The results for 
Mercury, given for another purpose, can also be extracted from the same 
place. For Venus and Mars, Newcomb unfortunately only printed the normal 
equations from which he deduces the constants of the orbit. 
On the screen is shown a slide (see below) which exhibits the results for the 
Earth and Mercury compared with those for the moon. In the uppermost 
curve are reproduced the minor fluctuations of the moon shown earlier; the 
second curve contains those of the earth’s longitude; the third, those of 
Mercury’s longitude. [By accident the mean motion correction has been left 
in the Earth curve; the zero line is therefore inclined instead of being 
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1750 1800 1850 1900 
horizontal.] It will be noticed that the scales are different and that the 
Earth curve is reversed. In spite of the fact that the probable errors of the 
results in the second and third curves are not much less than their diver- 
gencies from a straight line, I think that the correlation exhibited is of some 
significance. If it is, we have here a force whose period, if period in the 
strict sense it has, is the same as that of the effect: the latter is not then 
a resonance from combination with another period. We must therefore look 
for some kind of a surge spreading through the solar system and affecting 
planets and satellites the same way but to different degrees. 
The lowest curve is an old friend, that of Wolf’s sunspot frequency, put 
there, not for that reason, but because the known connection for the last sixty 
years between sunspot frequency and prevalence of magnetic disturbance 
