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APPENDIX. 
449 
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 thl 
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 constellation near which it appears and disappears; counting 
until its disappearance; the arc maybe 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. 
U. S. Ship Vincennes, 
At Sea, August 8th, 1839. 
In order more effectually to observe the periodical meteors which 
may be repeated, on the nights of the 8th, 9th, and 10th of August, 
the following officers will keep watch on those nights, and assist the 
officers of the watch in making observations. 
With the 1st wateh, Mr. Couthouy and Mr. Elliott. 
With the 2d watch, Dr. Pickering and Mr. Howison. 
With the 3d watch, Mr. Drayton and Dr. Fox. 
With the 4th watch, Dr. Gilchrist and Dr. Whittle. 
The officer of the watch will assign a quarter of the heavens to eacli 
person in his watch, who will note at once on paper, any meteors that 
may be visible, 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 this on a meteor, 
yet it is possible, and even easy, viz., by noting the star of the con- 
stellation near which it appears and disappears; counting until its 
disappearance ; the arc may be accurately measured by a sextant ; 
VOL. I. 
113 
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