Analysis of Mr Barlow's Essay cn Magnetic Attractions . 267 - 
lysis of his work. The leading principle of the preceding laws, 
and that upon which they all rest, is the existence and particu- 
lar position of the plane of no attraction, which, as we have 
seen, forms in Woolwich with the horizon, an angle equal to the 
complement of the dip ; and generalizing from this individual 
fact, Mr Barlow concluded that it was the same in all parts of 
the world ; consequently, on the magnetic equator, that plane 
will be perpendicular to the horizon, and a ship being put round 
in this place, ought to pass through four points of no attraction, 
viz. at E. W. N. and S.; whereas, hitherto, the two former had 
been considered as the points of greatest attraction in all parts 
of the Earth. 
This, however, could only be considered as a probable con- 
jecture, till experiments had been made to verify it ; and it must 
therefore have been peculiarly gratifying to Mr Barlow, to find 
his views so fully and satisfactorily confirmed by the experi- 
ments of Mr Lecount, of which an account will be found in a 
future article of this number *. These experiments were made 
without any knowledge of what had been done by Mr Barlow, 
and are therefore the more satisfactory and conclusive. 
In the last two sections of his Essay, Mr Barlow indulges him- 
self in some speculations of a theoretical nature, which will pro- 
bably share the fate of various other hypotheses that have been 
from time to time advanced, to account for this mysterious ac- 
tion ; the first relates to the course of the diurnal variation of 
the needle, and the other to the general principle of magnetic 
action ; or rather, perhaps, we should say, that, in this last sec- 
tion, he has endeavoured to throw some doubt upon the present 
received doctrine, without advancing any new theory in its place, 
except slightly alluding to certain theoretical views of his col- 
league Mr Christie, of which a more particular account will be 
found in our present number. 
The author seems unwilling to admit that doctrine, which 
makes every mass of soft iron a magnet, from the action of a 
supposititious terrestrial magnet, and it must certainly be admit- 
ted to want one of the most essential characteristics of such a 
body. A magnet, whether natural or artificial, however weak, 
* See page 295. of this No. and also Vol. iv. p. 436;, 
