8 REPORT— 1850. ᾿ 
day, during which continuous observations were made in all the magnetical observa- 
tories in the world, was observed, in the same manner on Cheviot and at Makers- 
toun. On Cheviot, observations of both the magnetometers were made every ten 
minutes for the twenty-four hours of the term, by myself and my assistant, Mr. 
Hogg. At Makerstoun, the observations were made by Mr. Welsh, with two 
assistants. The times of the observations were strictly the same, as I compared the 
chronometer on Cheviot with the observatory clock at Makerstoun, in the manner 
which I described at Oxford. Mr. Welsh reflected the sun-light from a mirror at 
Makerstoun upon our position on Cheviot, and he cut off the reflexion at previously 
agreed on minutes and seconds of the observatory clock, by which means the error 
of the chronometer on Cheviot was accurately determined. The large mass of com- 
parative observations are only partially reduced, and it was only yesterday that, with 
Mr. Welsh’s assistance, 1 have been able to complete the reductions to a sufficient 
extent to present some of the results to the Section. I omit any notice of the pro- 
cesses employed in the reduction and combination of the observations. 
I have projected the hourly means from six days’ simultaneous observations at 
Makerstoun and Cheviot. The following are the conclusions which I have deduced 
from these means :— 
Ist. The diurnal ranges of magnetic declination at Cheviot and Makerstoun in 
the end of the month of August, probably do not differ one-tenth of a minute, the 
difference of heights of the stations being nearly half a mile. 
The following are a few specimens of the simultaneous changes of declination at 
the two places :— 
Difference of the highest and lowest hourly means, | Cheviot . . 15'42 
from six days’ observations, as in the curves . Makerstoun 1541 
Difference of six highest and six lowest hourly means, | Cheviot . . 12/58 
ΔΒ ἸΏ ΠΗ ΟΠ ΡΜ tee co Se eh ς ΤΠ το eke 5 Makerstoun 1250 
Mean difference of a series of maxima and minima ἢ Cheviot . . 13/50 
occurring simultaneously during six days . . Makerstoun 13/40 
Greatest range in any of the six days occurring | Cheviot . . 20"71 
SUMULEANCOUSLY, Wisc Pere hts aed tee teen Tork 6 Makerstoun 20'62 
In no case does the difference of ranges exceed one-tenth of a minute. Asa 
further evidence of the exactness with which the two magnets followed each other, 
I may state that the differences of the change of declination at each station, for any 
two hours of the same day, do not differ from each other more than can be explained 
by error of observation, and by the apparent law, which I shall state immediately. 
This remarkable result for the ranges, differs from that which I conceived was 
exhibited by the June observations ; they appeared to show a greater range at Ma- 
kerstoun than at Cheviot, by nearly one minute. I have already mentioned the 
sources of error to which the June observations were liable ; but I should also notice, 
that the conclusion, as to the difference of ranges, was obtained from the mean 
of only three days’ observations, to which I have no hesitation in giving a much 
smaller value than to three days in August. Besides this, however, upon taking five 
of the greatest ranges obtained in the June observations, during which the instru- 
ment seemed moderately steady, I find 
Cheviot . . 1816 
Makerstoun 1820 
or almost exactly the same. I consider, therefore, that the August observations 
may be taken as conciusive, that the difference of ranges at the two stations is not 
more than one-tenth of a minute, the greatest range probably occurring on Cheviot. 
2nd. The maximum of westerly declination occurs rather sooner, or nearer noon, 
at the highest station. 
This conclusion was also arrived at from the June observations. I have projected 
the differences of the ordinates of the curves for Cheviot and Makerstoun on ten 
times the scale: from this projection it will be seen that the declination magnet 
moves more rapidly westwards in the forenoon at the upper than at the lower sta- 
tion, and that it begins to move eastward again at the upper station sooner than at 
the lower, so that the difference of ordinates diminishes with the greatest rapidity 
for two or three hours after the maximum. I have also projected the difference of 
Mean ranges from the June observations . . 
