2ir 



reach the giouiid. This wai crtrtiuly sutti'it'iitly exact, and there were trees 

 which cuuld not be accurately measured in any other way : for instance, if 

 placed in the miildlo of other trees, or if they had a flat wide Rereading top. 

 It was nevertheless a vulgar and unscientific plan, and had such self-evident 

 difficulties that he need not point them out. 



The third plan was as pretty as it was simple and easy : the measurement 

 by the shadow. Where the highest point of the tree is prominent and the 

 ground is perfectly level (or if its rise or fall keeps exactly to the same 

 inclination), this method is quite accurate. The plan is as follows : To 

 stick upright a stick, three feet high, just at the point where the shadow of 

 the top of tlie tree ends, then take the length of the shadow of the stick. 

 The stick's shadow will represent a yard, and you have then simply to 

 measurs by it the distance to the trunk of the tree. This plan though often 

 applicable is i>retty sure not to he so with the particular tree you may wish 

 to measure. 



The fouith method is with the mirror. Place a small looking-glass hori- 

 zontally on the ground between yourself and the tree at such a distance that 

 you can see the reflection of the top of the tree in the glass. Now, since the 

 angles of incidence and reflection of a ray of light are always the same, it 

 follows that the angle from the tree top to the mirror must be the same as the 

 angle from the mii-ror to the eye of the observer. Having measured the 

 distance from the base of the tree to the mirror (by way of illustration let 

 us suppose it 100 ft.), multiply this by the distance of the eye of the observer 

 from the ground (say 5 ft.), and divide the product (500 ft.) by the distance 

 from the mirror to the heel of the observer (siy 6 ft.), and the result will give 

 you the height of the tree (83 ft. 4 in. in this illustration). The mirror plan, 

 however, again requires that the ground should be perfectly level, and, 

 moreover, wants considerable practice even then to ensure its accuracy, fur 

 the smallest error in the multiplying or dividing figure would make a very 

 great difference indeed in the result. 



To the fifth plan he ^nust call their particular attention. Everybody now 

 who takes up any subject is expected to show some little originality, and in 

 giving the plans of other people, to have a better one of his own (a laugh). 

 Now this fifth plan was his own. He called it the skelcher's plan. Any of 

 them accustomed to sketch would recogi.ise the great use for keeping the 

 relative heights of objects, of holding up the pencil immediately before the 

 eye and thus measuring them. Mark a measured space on the tree and 

 substitute a pocket scale for the pencil, and you have the means of getting 

 its exact height. Let us suppose that you come to a remarkable tree. 

 You measure first, say the ciicurufereuce of the trunk, next you pin a card, 

 or back of a letter, on the bark of the bole, at exactly 6 feet from the ground, 

 and thon retire to such a distance from the tree as will enable you by holding 

 the scale against your eye easily to embrace the whole tree within it— 60 or 

 80 yards will generally be ample for this purpose— the space on the scale 



