Decay in gronsoing Larch and Spruce. 



385 



length of the side of this square is 4 in. A diagonal line is 

 drawn across from the angle c ; and parallel to this line, a brass 

 pendulum is suspended from a side pin. This pendulum has a 

 curved limb or finger e attached anywhere near its middle; and 

 the pendulum and curved limb are kept from flying off" the board 

 by two brass guards, which, however, admit the free action both 

 of the pendulum and curved limb. At the extremity of the 

 muzzle c, a sight is fixed, as in the barrel of a common fowl- 

 ing piece, to guide the eye ; and the but-end of the instrument 

 being applied to the shoulder, and the sight on the end of the 

 barrel part directed to the top of the tree, the operator advances 

 towards it or retires backwards till the point of the curved limb 

 is visible above the line of the stock, as in the figure. The cir- 

 cumstance of the curved limb being visible above the barrel part 

 of the instrument, proves to the operator that the plumb line 

 rests on the diagonal line of the square, and consequently that 

 the angle made by the eye of the operator with the top of the 

 tree is 45°. The distance of the operator from the tree, and 

 the height of his eye from theground, being then added together, 

 give the height of the tree; unless the ground should not be 

 level, in which case allowance must be made, either by adding 

 or subtracting, according as the ground may be lower where the 

 operator stands than at the root of the tree, or the contrary. 



This instrument, I believe, was in- 

 vented by Mr. Cuthbertson, the 

 head gardener at Studley Royal, 

 who was my constant assistant in 

 taking the measurements. 



It has occurred to me, that the 

 same principle might be exemplified 

 in a more portable instrument, and I 

 have accordingly contrived Jig. 48., 

 which is only 12 in. long on the 

 upper side. It is made of box, with 

 a brass octant suspended from its 

 centre, and loaded at the extremity, 

 with a curved limb, as in Jig. 48. 

 It is unnecessary to describe the 

 manner of using it, which 

 cisely the same as that of the preceding figure. 

 London, May, 1840. 



IS 



pre- 



Art. VI. On the Decay in growing Larch and Spruce Fir Trees. 



By J. WiGHTON. 



You have often taken notice of the decay in larch and spruce 

 fir trees, commonly called the rot, and invited opinions as to its 



