42 SEVENTH REPORT—1837. 
and accuracy of our knowledge of the course of the magnetic 
lines in those parts of Europe. The investigation evidently 
cannot be in better hands. Meantime I have not thought pro- 
per to make deductions which he has not made for himself; 
and the more so, because the stations are very few at which 
there are both observations of dip and of horizontal intensity, 
and at some of these the total intensity has already been de- 
termined by other observers. 
The preceding notices include all the observations of the 
magnetic intensity with which I am acquainted, in which the 
instruments, by the steadiness of their magnetism, and their 
capability of yielding sufficiently precise results , proved eed 
of the time and pains bestowed in their employment. 
Section I].—Generat Taste or INTENSITIES. 
The intensities are arranged in this table according to their 
values, commencing with those of highest amount in the 
northern hemisphere, descending progressively to those of 
least amount, which have their “places in the intertropical 
regions, and again ascending to the highest values in the 
southern hemisphere. They are classed in zones, the first 
zone (§ 1) comprehending all the observed intensities in the 
northern hemisphere between 1°85 and 1°75; the second 
zone (§ 2), all between 1°75 and 1°65; the third (§ 5), all be- 
tween 1°65 and 1°55; and so on. In each zone the record 
in the table commences with the geographical meridian of 
Greenwich, and passes round the globe in an easterly direc- 
tion ; all the longitudes being counted east from Greenwich, 
and all latitudes nor th, unless where it is otherwise distinctly 
specified. 
The geographical position of the several zones is shown in the 
maps attached to this report by the insertion of the observed 
intensities themselves in their places in the map. For the 
more ready guidance and direction of the eye lines are drawn, 
marking as nearly as can be judged, the middle of each zone. 
These lines are consequently what are usually denominated 
isodynamic lines, or lines of equal magnetic intensity at the 
surface of the earth. ‘They correspond successively to the 
values of 1°8, 1°7, 1°6, &c., down to 0°8, which is the line of 
lowest value yet observed. There is, of course, great ine- 
quality in the evidence for their precise geographical position 
in different parts of the globe; sometimes, for the purpose of 
connection, they have been partially continued where obser- - 
Br gr ee ae Le 
