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ŠUMARSKI LIST 5-6/1958 str. 69     <-- 69 -->        PDF

of height). Teschendorf´s and Stoffels´ theories are the logical ones and it is very
likely that with careful and slow work results can be obtained according to this
theory. But our experiment was carried out under conditions prevailing in practice
when under the strees of measuring a great number of heights, there occurs a relaxing
of attention. It is very likely that in this case the following occurs: first, the
measurer equipped with Christen hypsometer sights through the lower and upper
edge of the rule slot whereafter he once more controls these lines of sight and then
he takes up reading in the line of sight to the staff top. This line of sight lying
always within the lower half or quarter of the scale, the measurer, before reading
off the staff top once more tries to sight the staff bottom exactly, and thus usually
displaces the rule and spoils the line of sight to the tree top. Therefore the line of
sight to the tree top is not equally accurate as the other two lines of sight. Stoffels´
theory assumes all three lines of sight to be equally accurate. If Stoffels´ formula
is written in a rather more explicit form


H If
aH = /

where 01, 02 and 03 are standard deviations of lines of sight on the rule referring
to the tree top, tree bottom and staff top, and if oi is relatively large as compared to
02 and 03 in such way that the amounts comprising 02 and 03 — using at the same


time a relatively large staff — may be neglected, we obtain a formula in which depends only upon the first power of height.


The same error due to fatigue appears also in Hub´s hypsometer. First, the
measurer sights the staff without preliminarily bringing his head into the necessary
position that — without an effort — he is unable to catch with his eye the
line of sight to the tree top, and then he involuntarily rises also his head and reads
off a too great height (see Fig. 3). This error is of systematic character while the
error — due to fatigue — in the case of Christen hypsometer has a random character
and therefore the Christen hypsometer is better and more suitable, if other sources
of systematic errors are excluded.


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