244 



PHYSICAL GEOGRAPHY. 



For the sake of facilitating further determinations, I present also the 

 directions for the selection of tertiary stations. Persons who desire to 

 obtain the exact positions of conspicuous landmarks in the vicinity of 

 Prof. Quimby's work, only need to follow these directions, and in due 

 time they will receive the results of the calculations. 



Directions for the Selection of Tertiary Stations and the Erection of Signals for the 

 United States Coast Survey, and the operations connected therewith. 



1 . Tertiary stations should be upon those hills which command the best view of the 

 surrounding country, particularly within a radius of six to ten miles. It is not so 

 important to secure a distant view as that the signal should be visible from the valleys 

 in the more immediate vicinity. It must also be visible from at least three secondary 

 stations. 



2. Having chosen the hill upon which a signal is to be erected, select that spot for 

 the station where the signal can best be seen from all directions, taking care that the 

 ground be as level as possible for a few feet around the station, for the convenience of 

 placing an instrument over it. 



3. The method of marking permanently the station wiU depend on the nature of the 

 ground. If the ledge is within three feet of the surface, remove the earth and drill a 

 five-eighths inch hole four inches deep, in which set with lead or sulphur an iron bolt 

 projecting three inches above the ledge. If the ledge is near the surface, cut a small 

 equilateral triangle in the rock around the bolt (say each side nine inches) , one of the 

 sides being north and south, and the opposite vertex pointing to the east. 



If there is no ledge within three or four feet of the surface, dig to that depth and set 

 a stone jar or some piece of pottery which will accurately mark the station, and be 

 readily recognized when found. Pack the earth carefully around and above this to the 

 depth of twelve inches, upon which place a piece of plank with a half-inch bolt firmly 

 set in it and projecting upwards three inches exactly over the station, as marked by the 

 jar. 



4. Select for the signal a straight pole (from which it is better to remove the bark) 

 six or eight inches in diameter at the butt, and twelve or fifteen feet long. Bore a hole 

 in the centre of the butt to receive the bolt set in the ledge or plank, and fasten to the 

 top of the pole a nail keg, ten to fifteen inches in diameter, so that the centre of keg 

 and pole shall coincide. This may most readily be done by inverting the keg (one head 

 being out) upon the pole and nailing through the other head, at the same time bracing 

 firmly the lower end of the keg. Cover this keg with black cambric, and the pole 

 below the keg with alternate bands of white and black. Set the pole thus prepared 

 over the bolt, and support it in a vertical position by filling around with earth, or if on 

 a ledge by a pile of stones, and also by braces or wire guys, as the circumstances per- 

 mit or require. Too great care cannot be taken to place the pole exactly vertical, and 

 to secure it from being moved by winds, cattle, or any other cause. To secure 



