APPENDIX. 565 



insurmountable difficulties should render it impossible to pursue the 

 course specified, and in no case are you to go to the southward of 

 the limits pointed out. 



Wishing you success in the execution of these instructions, 



I am, &c., 



Charles Wilkes, 



Commanding Exploring Expedition. 



Lieutenant R. E. Johnson, 



U. S. Brig Porpoise. 



142 



