Sun-spot Areas and Diurnal Temperature-Ranges. 291 



perhaps find that the magnetic declination-range was largest when 

 there were most sun-spots. If, however, we were to make a similar 

 comparison between sun-spot daily areas, that is to say, the daily 

 aggregate areas occupied by spots including penumbra?, and diurnal 

 temperature-ranges, we might not obtain a decisive result. For at 

 certain stations such as Toronto, it is suspected (the verification or 

 disproval of this suspicion being one of the objects of this paper) 

 that there are two maxima and two minima of temperature-range for 

 one of sun-spots. This is not a phenomenon unknown in other 

 branches of meteorology, as for instance in barometric pressure, which 

 has two oscillations in one day. Its effect, however, might be such 

 that, in a comparison made as above, the temperature-range corre- 

 sponding to a maximum of sun-spots might be equal in value to that 

 corresponding to a minimum, or, in other words, we should get no 

 apparent result, while, however, by some different process, proofs 

 of a real connexion might be obtained. 



But if we can get evidences of apparent periodicity in sun-spot 

 fluctuations when dealt with in a particular manner, we have a 

 method which will afford us a definite means of comparison. And 

 here, as Professor Stokes has pointed out, it is not necessary for our 

 present purpose to discuss the question whether these sun-spot 

 Inequalities have a real or only an apparent periodicity.* All that 

 is needful is to treat the terrestrial phenomena in a similar manner, 

 or in a manner as nearly similar as our observations will allow, and 

 then see whether they likewise exhibit periodicities (apparent or 

 real) having virtually the same times as those of the sun-spots the 

 phases of the two sets of phenomena being likewise allied in a con- 

 stant manner. It is such a comparison that we have here made, but 

 before describing the results obtained, it will first be necessary to 

 describe the method of analysis which we have adopted. 



Method of Analysis. 



3. Our method is one which enables us to detect the existence of 

 unknown Inequalities having apparent periodicity in a mass of 



* It is well known that when we discuss a series of figures, we frequently detect 

 peculiarities of some kind, which strike the eye but hare no scientific meaning. 

 Such peculiarities might occasionally assume the form of apparent periodicities, and 

 there is no reason why they should not manifest themselves when the figures we are 

 discussing represent the progress of some natural phenomenon. Moreover, in this 

 last case we may sometimes perceive irregular attempts at repetition, such as we 

 observe in volcanic phenomena, to which, however, we are unable to assign any true 

 periodicity. Now it is imaginable that such appearances as we have indicated above 

 may take place in our list of sun-spot areas without implying the presence of true 

 periodicity ; but whether such marks of periodicity as those records present be real 

 or only apparent, inasmuch as they do occur we should expect them likewise to occur 

 in siich terrestrial phenomena as are closely connected with sun-spots. 



