APPENDIX. 401 
between the flash and report ; then, or before, measure the azimuth 
between each vessel and the sun, and proceed with your boats to 
sound, radiating from each vessel on the several points of bearings : 
the position of your boats may be accurately ascertained by the 
angles on any three of the vessels, and the soundings obtained can at 
once be inserted on the skeleton chart prepared for the occasion. 
You will, while at anchor, heave the current-log every hour, and 
notice the direction by the head of your ship. After you have satis- 
factorily explored the ground that your vessel may have anchored on, 
you will then, in all probability, know the direction in which the 
shoalest water lies from you, and by shifting the anchorage of each 
vessel in succession toward that direction, you will occupy new 
ground, when the same operation of measuring bases by sound, and 
taking azimuths, will be gone through with, and then you may 
approach the position without any danger, as your chart will be 
constructed as you proceed. 
Lieutenant Johnson has been ordered to the Porpoise to super- 
intend her movements in regard to this survey, and Lieutenant 
Alden to your ship, in whose information, as respects the above mode 
of proceeding, you may rely. 
Mr. Knox, of the Flying-Fish, is also apt at this work. I have 
ordered Mr. May to assist him in this cruise, and Mr. Eld, of your 
ship, to assist in the duties on board the Sea-Gull. 
After you have obtained the necessary information in regard to 
this shoal, (should you be so fortunate as to find it,) you will return 
to Cape Frio, and from thence measure the distance from this harbour 
by sound. 
The most efficient mode of doing this, I conceive as follows, viz. : 
After getting the light in sight, anchor the three vessels so as to form 
a triangle, and take their azimuthal bearings from the sun, measuring 
by sound the distance between the vessels, which will give you the 
bases of the triangle, then measure the angles from on board the 
vessels, with the light-house, and this will give you data to calculate 
its distance and bearing, thence proceed west, keeping the vessels in 
range, and as soon as you get their distance and bearing change their 
positions alternately. 
Very respectfully, 
Charles Wilkes, 
Commanding Exploring Expedition, 
Captain William L. Hudson, 
Commanding U. S. Ship Peacock. 
VOL. I. 101 
