On Measuring growing Timber. 261 



trap rocks of the Ochills, and a little of the red sandstone of the 

 district, which form the basis of very excellent soil. The tree 

 is still of vigorous growth. I had measured it, in 181*7, exactly 

 in the same manner; and in 1832 it was 15 ft. higher, and had 

 laid on some SO cubical feet of timber. 



The height of trees, or any other object, is easily taken by 

 the pocket sextant; and the angle of 45° is the most convenient 

 to obtain it without calculation. Other angles are sometimes 

 used for a different proportion of the base, but are not so certain 

 in practice. It requires, however, some experience in the use 

 of it to take the diameter correctly. But the trouble of acquiring 

 this practice will be well repaid by the numerous uses to which 

 this excellent instrument is adapted, for the purposes of practical 

 men and amateurs. Some of them are fitted with a small level, 

 which enables the height of the eye to be marked correctly 

 above the root of the tree ; but this can be done with sufficient 

 correctness by suspending a plumb line from the sextant, and 

 setting it at 90°; when the reflected image of the plummet upon 

 the tree will mark the point ; but, generally, for all the purposes 

 wanted, the point can be ascertained with sufficient correctness 

 by the eye. 



Second Method. — It will be seen that the first mode is only 

 for amateurs, or for very particular cases in business, such as 

 the examples narrated ; but this second mode is completely prac- 

 tical, and, I may say, even forced upon me from the necessity 

 of the case. Having been employed to mark and value a large 

 quantity of full-grown timber for a particular object, I found the 

 mode of taking the girt within the reach of a man very unsa- 

 tisfactory, the trees being of very great height. About the same 

 time, having heard of Mr. Monteith's machine, and having got a 

 sight of it, I saw that it was unsuitable for despatch in business, 

 and felt much disappointed : but the thought immediately oc- 

 curred, that the quarter girt might be as readily ascertained 

 from the diameter as the circumference, and as correctly as cus- 

 tomary measure requires. Thus, by the application of a diameter 

 gauge, this would be done with the requisite despatch. 



The gauge which I then devised, and, with few exceptions, 

 have used for seventeen years, consists of three flat pieces of 

 wood, 2 in. broad, and a quarter of an inch thick, put together 

 so as to form three sides of a parallelogram ; the largest side, or 

 scale arm, being fully longer than the diameter of the timber to be 

 measured; and the other two, or tangent arms, a little more than 

 one half of the scale arm. One of the tangent arms is screwed 

 fast upon the end of the scale at the zero, their interior edges 

 forming a true rectangle at that point; and the other tangent 

 arm is made to slip upon the scale with a rectangular motion, 

 and can be drawn backwards and forwards by means of a cord 



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