32 Royal Society : — 



A sufficient body of the larger disturbances to permit an exami- 

 nation of their laWs having been separated from the rest of the ob- 

 servations, it was found at Point Barrow, as elsewhere wherever a 

 similar investigation has been made, that in regard to the frequency 

 of their occurrence, and to the mean amounts of easterly and west- 

 erly deflection produced bj' them, the disturbances follow system- 

 atic laws depending on the hours of solar time. The laws of the 

 easterly and of tlie westerly disturbances were also found, at Point 

 Barrow as elsewhere, to be distinct and dissimilar. On further in- 

 stituting a comparison between the disturbance-laws at Point Barrow 

 and Toronto, it was found that although the laws of the deflections 

 of the same name at the two stations did not correspond, there 

 existed, on the other hand, a very striking and remarkable correspond- 

 ence between the laws of the easterly disturbances at Point Barrow 

 and of the westerly at Toronto, and between the laws of the westerly 

 disturbances at Point Barrow and easterly at Toronto. The corre- 

 spondence is traced in much detail, for the purpose of showing that 

 it is manifested, not in slight and unimportant particulars, but in the 

 most marked characteristics of both classes of phenomena. From 

 the correspondence in the hours at which opposite disturbance-deflec- 

 tions prevail, it follows, that the portion of the diurnal variation 

 which depends upon the disturbances, has opposite, or nearly 

 opposite characteristics at the two stations. 



In former papers the author considers that he has shown that, 

 for the piu'pose of obtaining a correct knowledge of the phenomena 

 of the regular solar rf»?;'?(«/ variation, it is necessary to eliminate the 

 influence of that portion of the observed diurnal variation which 

 proceeds from the disturbances ; and he now adduces the observa- 

 tions at Point Barrow as strongly confirmatory of this. When the 

 diurnal variation is derived from the whole body of the observations 

 at Point Barrow, retaining the disturbances, the westerly extreme of 

 the diurnal excursion, Avhich, as is well known, occurs generally in 

 the extra-tropical part of the northern hemisphere at a little after 

 1 P.M., is found to take place at 11 p.m.; but when the larger 

 distvxrbances are omitted, the westerlj^ extreme falls at the same 

 hour as elsewhere, viz. a little after 1 p.m. The author takes 

 occasion to suggest the probability that the anomalies which have 

 ])een supposed to exist elsewhere in the turning-hours of the solar 

 diurnal variation in high latitudes may be susceptible of a similar 

 explanation. 



It appears, therefore, by the comparison of the Point Barrow and 

 Toronto observations, that in the regular solar diurnal variation the 

 jirogression at the two stations is similar, the easterly and westerly 

 extremes being reached nearly at the same hours ; whilst in the 

 disturbance diurnal variation the progression is reversed, the easterly 

 extreme at the one station coinciding very nearly with the westerly 

 extreme at the other. This contrariety seems the more remarkable, 

 since both variations appear to have the same primary or exciting 

 cause, viz. the sun ; inasmuch as in each the period is a solar day. 

 The author draws the probable inference, that whilst the primaiy 



