Popular Science MontJdi)

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��A Simple Instrument Which Measures the Height of a Tree

EXPERIKNC"1-:L) foresters become expert in jutiging oft-hand the height of average timber. By merely looking at a tree of medium height they are able to make a guess with a degree of accuracy that is sufficient for roughly estimating the number of board feet of lumber it contains. But in the case o timber two hundred feet or more in luight c\cn the most expert woodsman is apt to make an error of from ten t(j twenty feet in his calculations. Errors of this kind greatly impair the value of an estimate of the amount of timber in a tract that perhaps is measured by hundreds of acres.

By the use of the hypsometer, however, the height of the tallest of timber can be ascertained with a remarkable degree of accuracy. There are a number of types of hypsometers, but all of them operate on about the same principle.

One that has been adopted by the Forest Service consists of a round instrument about four or five inches in diameter and an inch in thickness. To one side is attached a convenient handle. Within the instrument there is a device which operates on the principle of a pendulum. Attached to this is a celluloid scale. On the outer edge of the instru- ment is a small peep-hole on one side and opposite it a square window-like opening somewhat larger in size. There is a convenient device for securing the pendulum at a fixed position.

To ascertain the height of a tree by means of the hypsometer, the operator takes a sight at liie wL proper point on its "-

trunk by looking through the peep- li o 1 e and out through the open- ing on the opposite side of the instru- ment. Three differ- ent heights figure in timber calcula- tions. One is calk'd the merchantable jhe dog is harnessed length. In making structed and equipped

���The height of a triru can be accurately n-.easured by look- ing through a slot. The figures are noted on a celluloid scale as on the kft

��certain estimates the "clear" length is ascertained, while in other instances consideration is given only to the height from the ground to the first limb of appreciable size.

The height of the tree governs the angle at which the operator holds the hypsometer in taking the sight.

���In His Merry "Dogmobile." How a Cripple Gets Along in the World

ALTHOUGH he is a cripple, R. A. Burdick of Los Angeles, has traveled ,^^ nearly five thousand miles "^Uliil in a single year with the aid ^\SK1 "^f ^ P'-'l dog Trix. The dog ^ Hf , is harnessed to a speci-

all>' built t r i cy cle eciuipped with handle- bars, headlight, tail- light and a scat sim- ilar to that used on wheel-chairs.

He sells newspapers and chewing gum. When he wishes to stop he presses a leather pad to a specially con- to the wheel, and the tricycle-whed chair dog stops immediatelj'.

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