160 Atlantic ^tearn Navigation. 



stances, at different times, in a peculiar deep blue, but not linear, 

 cloud, resting on the horizon in the north, in the day time ; its 

 center of gravity being exactly, or almost exactly, in the mag- 

 netic meridian. Vf henever 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 j)osition 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 situated, 

 he may appear to have drawn upon his imagination. Did time 

 and space permit, he might give more particulairs. He hopes oc- 

 casionally to resume this andldndred subjects, so. far as his pres- 

 ent residence in a latitude less favored by auroral exhibitions, and 

 his more exclusive devxDtion to professional duties will alloAv. 



Art. XIY .—Lette7'S on Atlantic Steam Navigation. 

 - By Junius Smith. 



LETTER I. 



London, 30th July, 1833. 



__ - TO BENJAMIN" SILLIMAN, ESf^. 



Dear /S'tr— Perceiving from your daily and periodical journals, 

 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 re- 

 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 propielling a ship.. It will be suflicient if I show that 

 the application of steam power is both safer and more philosophi- 

 cal than the power of wind in navigation. 



If you direct your attention, to a sailing ship, you will find that 

 she has /thre'e- masts ; that these masts are vertical levers ; and of 



