304 TERRESTRIAL MAGNETISM.—MURPHY. 
Now, I think that I have said quite enough on the theory of 
the subject for my purpose this evening. I shall now advert to 
the practical adaptations of magnetism that enter into the experi- 
ence of our daily life. The compass, with its prime importance to 
navigation, is perhaps the most prominent, and the one that has 
been of the greatest benefit to man. 
We have already referred to the earth asa magnet; an iron 
ship is a magnet, and the compass that guides the ship is also 
a magnet. The earth, the ship, and the needle are but magnets 
of different intensities ; there is a very intimate though varying 
relationship between them; they are not amicable companions ; 
there is a constant struggle between them for mastery; they 
have certain inherent properties in common; and to these pro- 
perties and to this struggle we may attribute the essential char- 
acter of the compass and its convenience, use and benefit to 
mankind. 
To relate what is known regarding the early knowledge, 
history and development of the compass is beyond the scope of 
this paper. I shall merely remark that Baron Humboldt says 
that reference to the use of it is to be found in Chinese history so 
remote as 2634 B.C. From writers on the subject, it does not 
seem improbable that a knowledge of the mariner’s compass was 
communicated by the Chinese to the Arabs, and through the 
latter was introduced into Europe. Hallam, in his Middle 
Ages, vol. 3, cap. 9, says: “the earliest definite mention as yet 
known of the use of the mariner’s compass in the middle ages 
occurs in a treatise written by Alexander Neckam in the 12th 
century.” It was not used in Scotland by King Robert in cross- 
ing from Arran to Carrick in 1306, as Barbour writing in 1375 
informs us that he had no needle nor stone, but steered by a 
fire on the shore. In 1750, Dr. Gowan found that the needles 
of merchant ships were made of two pieces of steel bent in the 
middle and united in the shape of a rhombus, and proposed to 
substitute straight steel bars of small breadth, suspended edge- 
wise and hardened throughout. He also showed that the Chi- 
nese mode of suspending the needle conduces most to sensibility. 
In 1820 Professor Barlow reported to the Admiralty that half 
