260 Proceedings of the British Association. 



question has been since made by Col. Sabine, in the discussion of 

 the results of the first two years' observations, made at the Magnetic 

 Observatory of Toronto, under the direction of Lieut. Riddell. The 

 mode of examination is, for the most part, the same as that of Prof. 

 Kreil,-— namely, to separate the individual results, which differ from 

 the monthly mean, corresponding to the same hour, by a quantity ex- 

 ceeding a certain arbitrary limit ; to treat them as the effects of perturb- 

 ing causes ; and to examine the frequency of their occurrence at the 

 several hours of regular observation. By this mode of examination 

 Col. Sabine has been led to the result — a result partly agreeing with 

 and partly differing from that deduced by Prof. Kreil — that " the 

 causes which produce easterly deflexions have their maximum fre- 

 quency of effect at ten hours, and those which occasion the westerly 

 deflexions their maximum at twenty hours. The minimum of both 

 occurs nearly at the same hour, viz. about two or four hours." Ana- 

 logous conclusions are deduced respecting the disturbances of the 

 horizontal intensity. These disturbances, which are on the whole sub- 

 tractive, have their minimum at 4 p.m., the hour of maximum inten- 

 sity ; their maximum, on the other hand, occurs about the time of the 

 nocturnal minimum of the intensity, or from ten to sixteen hours. 

 Col. Sabine then proceeds to compare the monthly means at the 

 several hours of observation, as deduced from the whole body of the 

 observations, and as deduced from the remaining observations, when 

 the excessive deflexions already referred to are laid aside. Of the 

 propriety of this separation, and of the results thence deduced, Dr. 

 Lloyd said that he would not now speak; as the remarks which he 

 had to offer had no immediate connection with that question. With 

 respect to an annual period in these remarkable phenomena, Prof. 

 Kreil and Col. Sabine have arrived at different conclusions. Accord- 

 ing to Prof. Kreil, " the perturbations are much more frequent in 

 the winter than in the summer months ;" and that, not merely because 

 the cause which produces the regular diurnal change is then more 

 feeble, but also because (according to Prof. Kreil) the disturbing 

 forces are then actually of greater intensity. According to Col. 

 Sabine, " the disturbances [of declination] appear to be distributed 

 throughout the year without any marked inequality either as to num- 

 ber or direction," except that their number appears to preponderate 

 somewhat in the month of October. With respect to the horizontal 



