1884.] Sun-spot Areas and Diurnal Temperature-Ranges. 23 



established as the former, at least if we compare together Inequal- 

 ities of long period. It has been attempted to explain this by 

 imagining that for long periods the state of the atmosphere as regards 

 absorption may change in such a manner as to cloak or diminish the 

 effects of solar variation by increasing absorption when the sun is 

 strongest and diminishing absorption when the sun is weakest. 



On this account it seemed desirable to the authors to make a com- 

 parison of this kind between short-period Inequalities, since for 

 these the length of period could not so easily be deemed sufficient to 

 produce a great alteration of the above nature in the state of the 

 atmosphere. 



The meteorological element selected for comparison with sun-spots 

 was the diurnal range of atmospheric temperature, an element which 

 presents in its variations a very strong analogy to diurnal declination- 

 ranges. 



There are two ways in which a comparison may be made between 

 solar and terrestrial Inequalities. We may take each individual 

 oscillation in sun-spot areas, and find the value of the terrestrial 

 element corresponding in time to the maximum and the minimum 

 of the solar wave. If we were to perform this operation for every 

 individual solar Inequality, and add together the results, we might 

 probably 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 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. The eect of this might be that in such a comparison 

 the temperature-range corresponding 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 other process proofs of a real connexion might be obtained. 

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

 tuations when dealt with in a particular manner, we have at once 

 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 the observations will allow, and 

 then see whether they also exhibit periodicities (apparent or real) 

 having virtually the same times as those of sun-spots, the phases of 

 the two sets of phenomena being likewise allied to one another in a 

 constant manner. 



