tween, could be ignored. Then the tripod was moved
consecutively to the floats 5, 4, 3 and 2, and the
respective micrometer readings registered together
with those of the corresponding settings of the
interference pattern in the laser line. The sequence
was concluded by readings at the terminal no. I
again. After a proportional reduction for the dif
ferences between the readings at this terminal the
intermediate readings may be compared with the
settings of the micrometer as calculated by inter
polation. The differences A would show at least
the order of magnitude of the influence of the
vertical refraction. The intermediate readings were
the mean of two series of 10 settings each. The s.d.
can be estimated as 1.6 pm (inclusive the s.d. of the
standardization) so that the s.d. of a difference A
would amount to 1.9 pm.
Four examples are given below, the first one show
ing the method of calculation, the last one showing
the largest difference A ever obtained. (Rounded
off to pm).
part of this influence by the inclusion of a liquid
level surface as a reference. One can measure the
vertical distance of two fixed terminal points of the
alignment in respect of this surface, calculate the
position of intermediate points by interpolation and
set the micrometer accordingly. The instrumentation
required is complex, but may be justified for specific
purposes. The instrumentation described is only
experimental and can of course be perfected for use
in practice.
A eknowledgements
The high precision instruments were built in the
workshop of the Department by Messrs. D. A. de
Wit and D. Joghems with exceptional skill. The
electronics was designed and built on specification
by the Technical and Physical Engineering Services
at Wageningen.
9
7
4 Conclusion
From the results it may be inferrred that the vertical
long term refraction has a more considerable
influence on an alignment than would be expected
at first sight. It seems possible to eliminate the larger
float 1 2 3 4 5 6
1st example
readings
7985
9054
7972
8196
8426
8637
8824
interp. for time*
13
10
8
5
3
0
reduced read.
7985
8206
8434
8642
8827
9054
earth curv.
0
1
2
5
8
13
correct, read.
7985
8205
8432
8637
8819
9041
calcul. interp.
7985
8196
8407
8619
8830
9041
differences A urn
0
+25
18
-11
0
2nd example
differences Aum
0
15
- 4
15
0
3rd example
differences A;j.m
0
16
18
+26
- 6
0
4th example
differences Ap.m
0
35
14
+48
19
0
infl. of evapor., temp. etc.
References
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Geodetic Survey no. I
Geilen, Q., 1971. Untersuchungen zur Richtungsstabilitat von
HeNe-Lasern mit Hilfe von Elektronischen Messlatten.
Veröff. Geodat. Inst. T.H. Aachen no. 19.
Van Heel, A. C. S., 1950. High precision measurements with
simple equipment. J. Opt. Soc. Am. Vol. 40, nr. 12, p.
809-816.
Jensen, H., 1950. Formulas for the astronomical correction
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ngt 76
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