Some Observations on the Mode of jMcasuring Timber. 91 



poses assume that the loss of timber caused by the reckoning in of the 

 bark is equal to the loss of timber consequent on the inexact system of 

 measurement. Yet in no cases, we must remember, is the deduction 

 for bark quite so great ; and in many cases it is very far from being as 

 great as the deduction to be made for inexact measurement. Mr. 

 Hoppus mentions i\j- or yV of the circumference as a fair deduction 

 for oak bark. A deduction of ^ from a circumference of 100 inches 

 will give a quarter-girth of Tl\ inches, instead of one of 25 inches. 

 The former girth, according to the "Tables," gives (with a length of 

 40 feet) 140 cubic feet 7 inches and fractions ; the latter, 173 cubic 

 feet 7 inches and fractions ; or a deduction of about 33 cubic feet 

 from the total contents measured with the bark. Reducing this to a 

 per-centage, we make a deduction of about 19 per cent, for bark- 

 Now the deduction made for inaccurate measurement was, we saw, 

 47| cubic feet, out of the contents, 221xV cubic feet; and this 

 reduced to a per-centage is about 20^ per cent. We see, therefore, 

 that the two deductions form a tolerably close approximation to one 

 another. We must remember, however, as we said, that y„ of the 

 circumference is about the largest deduction which should be made, 

 and that in the cases of other trees it should form a less proportion. 



We must remember, moreover, if we measure with the bark on, 

 and then make a deduction, that the question stands precisely as it 

 was before, and that we are treating the tree as if the bark were off. 

 It is to the latter cases that these remarks apply, and I repeat that if 

 in these cases we measure trees by the ordinary quarter-girth method, 

 we are losing 21^ per cent, of our property, whereas by measuring them 

 in a more exact manner we may add in all cases 26 per cent, to the 

 results already found, and if we take care to measure in more pieces 

 than one, we may add almost half as much again to the same. 



If, therefore, exactitude is an object to be attained, any of the 

 following courses is open to us : — Either, first, we must not deduct 

 the bark from the total contents in measuring trees with the bark on; 

 or secondly, if we do so, we must add 26 per cent, as much again, or 

 between one-fourth and one-third to the contents already found; or 

 thirdly, we must adopt a new system of mensuration. TJie most 

 obvious reform which presents itself, and one which obviates the 

 necessity of calculating new tables, would be to alter the spaces of 

 the quarter-girthing tape. We have to obtain a side which shall be 

 larger by 12'84 per cent, of inches than one quarter exactly of the 

 girth. We might make the 4-inch spaces therefore somewhat less, 

 and yet number them 1 inch, 2 inch, 3 inch, &c., as now. If this 

 were calculated out, a correct result would at once be attained. Or 

 we might start from another datum than that of the quarter-girth. 

 We might take the whole girth, and calculate out the result by the 



