OF THE MAGNETIC DECLINATION AT POINT BAEEOW. 
511 
cise conclusion, than that the observed ranges appear to be nearly in the inverse propor- 
tion of the respective values of the horizontal force. 
But when we turn our attention to a comparison of the magnitudes of the range of 
the disturbance-variation at the two stations, we cannot fail to be impressed with the 
excessive disproportion which we perceive between the decrease of the earth’s horizontal 
force and the increase in the range of the disturbance-variation at Point Barrow, when 
compared with Toronto. At the latter station the whole range of the mean diurnal effect 
of the disturbances scarcely exceeds 2'’0, whilst at Point Barrow it is not less than nine 
or ten times that amount. The disproportion would have been still greater if the colli- 
mator scale of the Point Barrow declinometer had permitted the distm’bances of largest 
amount to have been registered at their full value. During the seventeen months of 
observation the magnet was forty times* deflected beyond the limits of the scale; in 
such cases the extreme cognisable dirision on the side of the deflection was the amount 
entered in the Table, although, of course, the actual deflection must have been greater. 
The collimator scale comprised 160 divisions, each of the value of 2'’287 ; and as the 
mean position corresponded nearly with the 80th scale-division, it follows that when a 
deflection exceeded about 180' (or 3°) on either side of the mean position, the excess, 
could it have been registered, must have mcreased,pro tanto^ the sum of the disturbances. 
The disproportion would also have been considerably greater, if the amount adopted as 
the standard value of a large disturbance at Point Barrow, and employed in separating 
the observations belonging to that category, had been more nearly proportional to the 
inverse ratio of the horizontal force there and at Toronto. In such case, all the observa- 
tions at Point Barrow, which differed more than about 10' from the normal at the same 
month and at the same hour, would have been classed amongst the large disturbances. 
But it was soon found that the disturbances at Toronto and Point Barrow bore no such 
analogy to each other. Even "with 22''86 (instead of 10') as the measure of a large dis- 
tmhance, the proportion of distuihed observations to the whole number was still much 
greater than at Toronto, where 5'’0 was taken as the measure of a large disturbance. 
It seems scarcely possible, therefore, to avoid the conclusion, that the average amount 
of deflection caused by the occasional disturbances at Point Barrow is very considerably 
greater, when compared with the same at Toronto, than can be explained by the differ- 
ence of the horizontal force of the earth at the two stations. 
A circumstance which strikingly accords with the excessive amount of the occasional 
disturbances at Point Barrow, is the great frequency with which appearances of the 
* Of the 40 instances in which the deflection exceeded the Limits of the recording scale, 30 were deflec- 
tions to the east and 10 to the west ; 24 occurred between the hours of 5 a.m. and noon, of which 22 were 
to the east and 2 to the west ; 22 of the easterly deflections occurred from 19*^ to 21^ inclusive, and 6 of the 
westerly from 11 p.m. to 1 a.m. inclusive. Deferring to Table V., it will be seen that, if the instrumental 
means had permitted these deflections to have been registered at their full values, the principal effect must 
have been to have increased the ratios of easterly disturbance at Point Barrow at the three hours of 19, 20 
and 21, which were previously the hours of its maximmn ; and in like manner to have increased the ratios of 
westerly disturbance at 11, 12 and 13 hours, which were the hours of its maximum. 
