“Now, for example, I am going to measure the distance to that tree over there. Get out your chain and measure off a straight line 10 feet long. Now, I’ll set the surveying instrument with the plumb-bob right over the end of this line, and sight through the two sight holes until I bring the two vertical hairs in line with each other and the tree. Look at the compass needle. It points to the 173 degree mark on the cardboard ring. Now, Bill, you hold the rod at the other end of our base line while I swing this instrument around and sight it. There, the needle points to 92 degrees, and subtracting this from 173 the difference, 81 degrees, is the angle at the right end of our base line. We’ll do the same thing at the other end of our line. See, the compass needle points to 189 degrees, and now sighting to the pole at the other end of the line we find that the needle points to 268. The difference, 79 degrees, is therefore the size of the angle
Fig. 84. Determining the Distance to the Tree. at the left end of our base line. Now we will draw this out on paper, as we did our first triangle, using quarter-inches to represent feet. Our base line was 10 feet long, and we will therefore draw a line 10 quarter-inches, or 2-1/2 inches long, on our drawing board. On this line we will construct the triangle, using the angles 81 and 79 degrees. There, that’s how our triangle looks, and the right hand side measures 7-1/4 inches, while the left hand side measures 7-5/16 inches. That is, 29 quarter-inches for one side and 29-1/4 quarter-inches for the other. As each quarter-inch represents a foot, you will find that the tree is about 29 feet from the right end of our base line and 29 feet 3 inches from the left hand end. Of course, our instrument is not perfect, neither is our drawing; but if you measure it off with the chain you will see that I am not very far from correct.”
Mapping the Island.
Most of our surveying was done by actual measurement, the surveying instrument being used only to determine the exact direction of the measurement. However, there were some measurements which we could not make directly with the chain. For example, we wished to know just how far it was from our tent to the Jersey shore of the river. We measured off a base line along our shore 400 feet long and sighted to a point directly across the river from our tent. The angle in front of our tent was 90 degrees, and at the other end of the base line was 73 degrees. When we drew out our triangle on the scale of 100 feet to the inch we found that the shorter side directly in front of the tent was almost exactly 13 inches long. This meant that the river at this point was 1,300 feet wide, nearly a quarter of a mile. On the other side of the island we found, in the same way, that the river at its narrowest point was about 500 feet wide. This portion of the river we named Lake Placid, as the water was very still and quite deep. This was due to a sort of natural dam formed at the lower end of our island. The small island that Dutchy found was kite-shaped, with a tail of boulders which extended almost all the way across to a rocky point on the Pennsylvania shore. The channel between “Kite Island,” as we called it, and Willow Clump Island was not more than fifteen feet wide in some places, and through this the water swept with a swift current down past a narrow neck of land to join the main current. This narrow stretch of land we named the Tiger’s Tail, owing to its peculiar shape. It was in the hook at the end of this tail that we discovered the old bridge wreck above referred to. From the tip of the Tiger’s Tail to Point Lookout, at the extreme upper end of Willow Clump Island, it was a little under a half-mile. The shore all along Lake Placid was very steep, except near Point Lookout. At one place there was a shallow bay which we called the lagoon.
CHAPTER VIII.
SWIMMING.
Fig. 85. The Diving Tree.