GENERAL SIR EDAVARD SABINE ON TERRESTRIAL MAGNETISM. 
267 
There was reason to hope that the Irish portion of the Survey would be repeated by 
Professor Lloyd, with the aid of other members of the Royal Irish Academy, who pro- 
posed that, when made, it should be printed in the Transactions of that Academy. 
For some time I cherished the hope that the English Survey would be accomplished, 
as before, by the joint labours of the original observers; and accordingly I commenced 
my share of the work in the summer of 1858; but as time advanced, it became evident 
that circumstances of health and the pressure of other employments and duties stood 
in the way of the hoped for combined operation. My own avocations would not permit 
me to devote to this object so much time consecutively as would have been required for 
its accomplishment in a single, year ; but by employing in it portions of the summers 
of 1858, 1859, 1860, 1861, and 1862, 1 obtained observations for the determination of 
the isodynamic and isoclinal lines at twenty-four well-distributed stations. The Decli- 
nation was supplied for several points on the coasts of the United Kingdom by Captain 
Frederic John Evans, R.N., F.R.S., from observations made by several naval officers 
between the years 1855 and 1861. A general notice of the results thus obtained was 
printed in the volume of the British Association Reports for 1861, together with the 
details of my own observations. 
Having premised this general historical statement I proceed to a more circumstantial 
notice of some points of detail. 
Corrections employed for secular change. 
A. Decimation . — The observations of the Declination comprised in the Survey supply 
six stations in Scotland at which that element was determined with suitable accuracy, at 
an interval in each case of nineteen or twenty years. The observers in all these in- 
stances were Captain James Ross at the earlier date, i. e. in 1838-5, and Mr. Welsh at 
the later date, i. e. 1857-5 or 1858-5. The details are as follows: — 
i 
Stations. 
Lat. N. 
Lerwick 
60 09 
Kirkwall 
58 59 
Wick 
58 25 
Golspie 
57 58 
Inverness 
57 28 
Aberdeen 
57 09 
Long. E. 
Observer. 
Date. 
358 53 
357 02 
356 55 
356 03 
355 49 
357 55 
f Ross, 
j Welsh, 
j Ross, 
j Welsh. 
Ross. 
Welsh. 
Ross. 
Welsh. 
Ross. 
Welsh. 
Ross. 
Welsh. 
1838-5 
1858-5 
1838-5 
1858-5 
1838-5 
1858-5 
1838-5 
1858-5 
1838-5 
1857-5 
1838-5 
1857-5 
Delination 
observed. 
Interval. 
Average 
annual 
decrease. 
Mean 
secular 
change. 
27 09 w. 
25 18 w. 
27 47 w. 
26 17 w. 
27 41 w. 
26 04 w. 
27 54 w . 
26 15 w. 
27 39 w. 
25 57 w. 
26 21 w. 
24 36 w. 
years. 
20 
| 20 
| 20 
| 20 
19 
19 
5-5 
4-5 
4- 9 
5- 0 
6- 4 
5-5 
> 5-3 
In the Philosophical Transactions for 1863, Art. XII., p. 291, it is shown that, at the 
Kew Magnetic Observatory (lat. 51° 29' N., long. 359° 42' E.), the average rate of dimi- 
nution of the Westerly Declination in 1858-59 was 6'-8 yearly (the decrease having 
been a little less in the years immediately preceding 1858, and a little more in the years 
2 n 2 
