160 Atlantic Steam Navigation. 
stances, at different times, in a peculiar deep blue, but not linear, 
cloud, resting on the horizori in the north, in the day time ; its 
center of gravity being exactly, or almost exactly, in the ‘mage 
netic meridian, Whenever the cloud was of this deep blue color, 
its direction was taken by the compass; and to avoid any bias 
from preconceived : theory, a point judged to be the centre of | 
gravity was selected, previous to the use of the needle. The 
variation from the meridian rarely. exceeded ‘a fraction of a de- 
gree; the correspondence in direction being more exact than that 
of the position of most polarized clouds. Had the writer been 
influenced by love of theory, he might have wished the latter 
and more explicable phenomenon to-be the more regular of the 
two. He would’invite the attention of more northern observers 
to this somewhat. mysterious phenomenon, should the return of 
auroral epochs reproduce it. To those less favorably age 
_ he may appear to have drawh upon his imagination. Did ti 
“and space permit, he might give more particulars. He Lope oc- 
easionally to resume this and kindred subjects, so far as his pres- 
ent residence in a latitude less favored by auroral exhibitions, and 
_his more exclusive devotion to professional duties will allow. 
= 
ie 
Ax. . XIV. —Letters on Atlantic Steam Navig zation. 
: ak Jonws Suirn.. 
<Any 2: ES rey gars “LETTER 1. | sae iT 
: * - London, 30th July, 1838. 
TO BENJAMIN SILLIMAN, ESQ. 
Dear Sir—Perceiving from your daily and periodical j ‘ournals, 
‘that Atlantic steam navigation is attracting public attention in the 
United States, and having been in some measure, instrumental in 
forming and maturing the plan here, perhaps the following te- 
marks may not be altogether uninteresting at the present moment. 
I do not mean to advocate the abandonment of the use of sails, 
whilst I shall endeavor to show that it is not a philosophical 
‘method of propelling a ship. It will be sufficient if I show that 
the application of stearn power is both safer and more phi losoph: 
cal than the power of wind in navigation. 
_ If you direct your attention toa sailing ship, you will find that 
she has three masts ; that eee levers ; and.of 
