428 APPENDIX. 



It is believed that when the Vincennes' masthead subtends an angle 

 of 25', you will be three miles from her. 



After the signal is made to take stations, you will pursue that course 

 which will lead you to it as soon as possible. 



Immediately after the signal being made to measure azimuths, 

 observations will be taken between the sun and vessels, during the 

 taking of which observations, the ship's ensign will be hoisted at the 

 peak. 



You will, after we heave-to for the night, try the dipping-needles 

 and deep-sea temperature. 



You will calculate the time, so as to be near the flag-ship at night- 

 fall, and any signals that are made will be repeated to the vessel 

 farthest off. In case of appearance of bad weather, you will at once 

 draw to close order of sailing unless otherwise directed. 



It is desirable that all calculations should be made before the day 

 closes. The current should be tried daily, either morning or evening. 



I am, &c, 



Charles Wilkes, 

 Commanding Exploring Expedition. 



Captain Wm. L. Hudson, 



U. S. Ship Peacock. 



U. S. Ship Vincennes, 



At Sea, August 8th, 1839. 



Captain Hudson will assign watches to the scientific gentlemen and 

 officers who are usually excused from watch, on the nights of the 8th, 

 9th, and 10th of August. One quarter of the heavens will be assigned 

 to each person, who will note at once, on paper, any meteors that may 

 appear, viz., their size ; with or without train ; their height ; the points 

 of appearance and disappearance ; and the time of flight. 



Although it may seem difficult to accomplish all of this on a meteor, 

 yet it is possible and even easy, viz., by noting the star of the constel- 

 lation near which it appears and disappears ; counting until its dis- 

 appearance; the arc may be accurately ascertained by a sextant; and 

 the bearing of the two stars, its true direction ; the counting compared 

 with a chronometer will be the true time ; and yet one has time to 

 examine its length of train, brilliancy, &c. 



Respectfully, 



Charles Wilkes, 

 Commanding Exploring Expedition. 



Similar instructions to Lieutenants-Commandant Ringgold and 

 Pinkney. 



