398 
MESSES. DE LA EUE, STEWAET, AND LOEWY’S EESEAECHES 
It will be seen from these numbers that the curves derived from these arbitrary periods 
are both less marked than the corresponding curves derived from the full periods, 
although the number of series summed together has been increased in the proportion of 
four to three. 
In conclusion, we may state that when we proposed that the present series of observa- 
tions should terminate in February 1872, we were under the impression that the period 
was nearer ten than eleven years. The results of this paper would tend to show that the 
period is over eleven years ; nevertheless we do not propose an extension of our series, 
for we think that the maximum will probably be reached before the proposed termi- 
nation. 
We ought also to state that in all probability the disturbances which we have hitherto 
registered are only those which occur in the lower regions of the sun’s atmosphere. It 
is therefore our intention to supplement our research on sun-spots with an evaluation of 
the faculse or bright patches, which are also signs of solar disturbance, but which occur 
in the higher and not in the lower regions of the solar atmosphere. The best method 
of doing this is at present engaging our attention. 
to the variation in the number of spots, and we have had it in contemplation to make direct observations of 
variability in the actinism of the sun in order to ascertain whether the period of greatest brightness is or is not 
coincident with that of the maximum of spotted area ; for it is not improbable that the sun may be the most 
brilliant when most spotted. 
A thorough examination of the solar photographs will no doubt do much to elucidate the subject, but 
these have the disadvantage of only representing with the greatest distinctness the faeulas Avhich are nearest the 
limb ; on the other hand direct actinic observations are interfered with by the ever varying conditions of the 
earth’s atmosphere, and also by the variations of the sun’s meridian altitude, so that it will be necessary to com- 
bine both methods of observation. 
