The following article was written by Heinrich Wild and published in the commemorative publication "Vermessungs-Grundbuch-Karte" on the occasion of the Swiss National Exhibition, Zurich 1939.
The modernisation of geodetic instruments had lagged behind that of other instrument types. Already in the last years of the previous century, very modern forms of binoculars, scarcely different from today's models, and shortly thereafter also rangefinders, were built on an entirely new basis. The designers of geodetic instruments paid little heed to this modernisation; their instruments retained the old, sometimes very old, forms, and the practitioner had to help himself as best he could. For example, in 1907 there was usually not even a thread, let alone a diopter division present for adjusting the eyepiece. The fine divisions of the silver circles and the pivots of the horizontal axis were mostly exposed; central clamps, so-called, appeared only occasionally. Spun thread was used for the fine crosshairs, some obtained from specially bred spiders. Special apparatus was constructed for thread stretching, but users were not provided with such equipment. Production consistently took place in small workshops.
Heinrich Wild, left, at the Rhône Glacier in the Swiss Alps, 1901.
With such an instrument, I conducted the triangulation of the Lower Valais at the beginning of this century. On September 1, 1902, in wonderful weather, I was early on the summit of the Dent du Midi and hoped to complete the measurements by noon. Instead, I had to "adjust" the instrument for about 2-3 hours, and when it was ready, the first signs of an approaching thunderstorm appeared. In the afternoon, we deposited the instrument on the summit in a sheltered place, carefully covered it with stone slabs, and began the accelerated descent. (Today, no one would likely leave their light instrument up there anymore.)
"As significant amounts of fresh snow fell, the continuation of work was only possible after several days. Although the intervening time could be filled with signal stations, etc., it was partially wasted. With a modern instrument that would have been ready for measurement immediately, I could have completed the survey in at most two hours."
It is natural that I was not particularly pleased with my instrument at that time, which incidentally was the best in the topographic office. Various considerations were made; however, as there was no understanding from the construction companies for improving the instruments, all attempts in this direction initially proved fruitless.
The first significant improvement occurred when the repetition system was abandoned. This eliminated the time-consuming "regulations" of the double-axis system and increased the accuracy of the measurements. However, a significant drawback immediately emerged: it was necessary to walk around the instrument while reading it, which prompted me to seriously consider designing a new theodolite for the first time (around 1905).
I contacted a Berlin-based company, which at that time was capable of making the most accurate circle divisions (Note: this can only have been Carl Bamberg in Friedenau), and the result was an instrument that no longer required circumnavigation but was unusable for other reasons because this Berlin company had no idea, by today's standards, of how to mount a somewhat more complicated optical arrangement correctly and permanently.
"This failure delayed modernisation by several years, and it wasn't until 1908, when I had access to the considerable resources of the Zeiss company in Jena, that the actual modernisation could begin."
When I arrived in Jena, there were no geodetic instrument designs, but there were experiences available for the precise manufacturing of the optical and mechanical parts, as well as their assembly. The microscope department produced very good screws, guides, and toothed gears; in the distance measuring department, optical and mechanical parts had to be securely stored in large quantities. There were more or less skilled designers, but they knew nothing about geodetic instruments.
I was personally only familiar with the handling and difficulties of using the instruments in the field; therefore, the chief designer for astronomical instruments was made available to me, and together we created the very first level instrument. The process with this first instrument was roughly as follows: I suggested that we should have a cylinder for the axis, and the chief designer said that this was certainly possible, leading to the borderline case of the non-regulating axis system, with a cylindrical axis made of material with the same coefficient of expansion.
With this, the axis question was settled for many years, as by continually improving the manufacturing process, genuinely good accuracy was achieved. Through my considerations, the biaxial telescope was then created, where one side moved as before in the main tube. Since sealing caused difficulties and at the same time, there was a desire for the shortest possible telescope, the arrangement with an internal focusing lens was created, which also allowed for better durability of the adjustment.
Now, a more accurate and convenient observation possibility for the level was still lacking, which was usable from both sides. For these somewhat refined requirements, my astronomical designer was no longer of much use to me, as these instruments were too distant from his field. Therefore, there was no alternative but to become the chief designer myself and set up my own design office. This resulted in the new prism system for the coincidence adjustment of the level, the arrangement of the reverse level together with the biaxial telescope, the modification of the lower part, etc., with protected screws.
Initially, these instruments were supplied with inadequate tripods; soon after, the new tripod with much greater strength and lighter weight was developed, which has persisted to this day. This tripod was the first (in early 1909) where clamping screws no longer had to be tightened during setup. In terms of containers, an initial attempt with metal was made at that time but was soon abandoned.
"Now there was a small level instrument with relatively high accuracy available, which did not cost significantly more, had much less weight, and allowed for faster work. Argentina and Russia were among the best customers at that time (in Russia, the average lifespan of an instrument of old design was estimated at three years). After the introduction of this first modernised instrument proved very successful, the larger types were built in quick succession."
At that time (around 1900), I had conducted precision levelling between Blei and Neuchâtel, after being instructed by the excellent Dr. Hilfiker. (Through various leveling operations on the Gurten near Bern.) For this levelling, I was provided with an instrument from Seibt-Breithaupt with a compensating staff. At that time, this instrument was the very latest; I had to try it out. These 30 kilometres, which took about a month, gave me the full experience of the instruments of that time: tightening tripod screws 600 times, reading poorly with a telescope 2400 times, carrying the heavy instrument 600 times, etc.
When I embarked on the design of the N.J. III in 1911, that beautiful spring month from eleven years ago had not been forgotten, and my first priority was to create a facility to work with a settling bubble. Since I already had the precise observation setup for settling the bubble in the coincidence prism system, the displacement of the target line of the telescope had to be added. To avoid any calculations, it had to be a parallel displacement. The thick plane-parallel plate placed in front of the objective was introduced with an adjustment mechanism that directly allowed the parallel displacement to be read in fractions of millimetres. The horizontal wire of the telescope was replaced by two wedge-shaped lines so that the 1mm thick strip could be comfortably centred at all distances. Only a device independent of wood, which is very moisture-sensitive, was suitable for the staff. As it was also necessary to eliminate the temperature influence simultaneously, the Invar band staff was designed.
It might be interesting to know how I achieved the very uniform and accurate division (approximately + 1/100 mm). I took a 3m long steel strip of a very specific hardness, a punch with a stamp in the form of lines, and with the help of a 1m long glass scale, the 3m template was punched in the design office, using which the staff divisions were sprayed for many years. I had decals made for the numbers.
The first completed precision level instrument went to the Fergana region in Russian Asia, and it turned out that shipping was only possible if the tripod was much shorter. Thus, the new tripod with retractable legs was created. With the new precision level instrument (with wedge line adjustment and Invar band staff), the majority of the new Swiss national levelling was carried out, for example. An event at that time was when England, initially quite reluctant, purchased 24 precision instruments in a short period and conducted the new English national levelling, along with other projects. The difficulties encountered during this modernisation are evident from the following example.
A professor, now deceased, explained to my representative during the first demonstration that the large diameter of the objective was dangerous for the accuracy of the measurements because too many "rays" were captured, causing disturbances. An intelligent assistant saw the advantages and eventually convinced the professor to approve the purchase. Several years later, with the new instruments under the supervision of this professor, the national levelling was completed, and the professor was converted. Meanwhile, the objectives have become even larger, and the "rays" have also fallen into this order.
In 1912, the design of new theodolites began. The first model was influenced by a larger order from a foreign state, which specified certain conditions (such as repetition device, estimating microscopes, etc.), so this instrument could only be partially modernised. By the outbreak of the World War, the future model had been determined to the extent that the main demands were met. The war completely interrupted the development, as civilian instruments were not allowed to be made until autumn 1918. In late 1918, I revived an idea from 1905, which had been buried as a pious wish, namely the principle of reading circles by coincidence of opposite lines (doubling the measuring interval). A small theodolite with second division in the field of view was created, and this instrument initiated the actual modernisation of the theodolite design.
"As the situation had become untenable due to the war, I returned to Switzerland in 1921, and the workshop "Heinrich Wild, Workshop for Precision Mechanics and Optics" was established in Heerbrugg in the Rhine Valley in St. Gallen. In fairly quick succession, the two sizes of the new theodolite model were created here, which could successfully compete with the products of the world company where I had been working shortly before."
While in 1908, the beginning was made with a small levelling instrument, in 1921, first the theodolites and only afterwards the levelling instruments were completed. Various other instruments were also developed, and as a main construction, a new autograph for the evaluation of photographic precision images. I began working on this autograph construction in 1920 after a conference that attempted to divide the world into two areas of interest for the two existing different models.
Since I owned the patents for this new autograph construction, the division of the world for the two other models was then omitted, and after the patent specification became known, it was only claimed that my construction was not feasible. Today, despite the alleged infeasibility, a large part of Switzerland has been newly mapped using this autograph, and the result appears in the new map sheets 1:50,000, as well as in the new overview plans 1:10,000 of the land survey. This autograph has also found considerable use abroad.
For this autograph, a discovery of crucial importance was made, which will be described in more detail below.
Until the spring of 1920, I had never considered incorporating photogrammetry into my work, although I had been encouraged to do so from various quarters earlier. However, the management of the Zeiss company believed that this area should be reserved for their employee, Dr. Pulfrich.
Since 1919, I had no longer been employed by Zeiss, but had promised to remain as a freelance employee in Jena until the spring of 1921. Since this was known, a proposal was made to me by another freelance employee, who was occasionally in Jena, to design an evaluation device where the handle should be firmly connected to the camera. This idea seemed so compelling to me that I immediately began designing such a device.
I had already made considerable progress with the design and was busy checking the general idea, i.e., the precise functioning of the apparatus. To my considerable dismay, during this check, it turned out that the basic idea, i.e., the fixed connection of the handle and the camera, was wrong. I dismissed my advisor with great disappointment and was initially at a loss.
"A stiff postcard with a pencil inserted through the middle (as an optical axis) had helped me in checking the functionality. I had marked points in the corners of the card or plate and let this plate holder make the movements that occurred in the device using the pencil (optical axis). This allowed me to discover the flaw in the design and set the matter aside for the time being."
After a few days, I revisited the card with the pencil and decided to determine where the points in the plate corners would actually need to be if the design were to work correctly. In doing so, I discovered the fundamental idea of the new autograph; it turned out that the incorrect and correct points in the plate corners lay on a circle whose center was on the optical axis (pencil). I had thus discovered that by giving the plate holder an additional movement around the optical axis, the arrangement worked correctly.
The further treatment of the idea was then of a mathematical nature; I determined the exact formula for the rotation angle r, and since this formula was not usable for mechanisation, an approximate formula was developed. This approximation formula reads: tan(r) = ½√(sina * tga * sinb * tgb) with an approximation that goes beyond practical needs. According to this formula, the additional movement of the plate holder was then arranged, thus finding an autograph on an entirely new basis, the construction of which could be kept relatively small. The accusation of mechanical impracticability was made by interested parties, apparently because this critic would not have been able to provide a mechanism in this regard.
The construction of this device with accuracy calculation took 14 days, mainly because none of the trigonometric functions contained in the formula were readily available for the apparatus.The field of photogrammetry naturally also required the construction of recording devices, photo-theodolites for terrestrial photography, and aerial cameras for aerial surveying.
The first photo-theodolites were equipped with Tessar lenses 1:6.3; f=150 mm because I did not have my own lenses available at the time. As the image quality towards the edge of the plate with these Tessars was inadequate, the redesigning of special lenses had to be undertaken. Two lenses were designed, 1:10 for the photo-theodolites and 1:5 for the aerial cameras, with focal lengths of 165 mm and 240 mm.
These lenses also provided sufficient sharpness for the outermost parts of the image for photogrammetry (a line-shaped object three seconds thick, meaning a thin white window frame at a distance of two kilometres, was sharply imaged). With these designs, the competitiveness of the new Swiss industry was proven.
As the so-called Koppe principle used in these autographs has certain shortcomings, I later provided a design that does not require the Koppe principle. I sold the relevant patents to the company Wild A.-G. in Heerbrugg at that time, which manufactured this autograph instead of my earlier one; the design itself is not mine.
In the so-called Koppe system, as is well known, the evaluation device uses the same or very similar lenses as the camera used for taking the photographs. (To neutralise any potential distortion.) This excellent principle, which could be compared to the elimination of axis errors in theodolites through measurements in the second position, has a drawback that does not lie within it but is determined by the current state of technology.
To this day, we still do not have a lens whose astigmatic correction provides field flattening across the entire extent of the image. In the lenses currently considered, within the range of 2/3 to 3/4 of the maximum image size, one or sometimes both of the astigmatic images deviate from the image plane, usually by amounts ranging from 1-2.5mm, depending on the focal length and type. Despite the lens's otherwise good correction, the plate still receives a sufficiently sharp image, making this error hardly noticeable.
However, when this flat (determined by the plate plane) image is transferred to the evaluation device and viewed with the same lens, the reversed astigmatism becomes fully apparent. This creates parallax, and since the 2/3 to 3/4 range is particularly important for control points, a point uncertainty arises here, which I found concerning regarding the subsequent image connection. Eliminating distortion is not among the difficult tasks, as I have explained before.
Only when lenses with completely flat fields of view are available will there be no further objection to the Koppe system.
For any potential similarity between the autograph I designed and Santoni's, it is best to compare the corresponding two German patent specifications, which show that Santoni's claims are directed quite differently from my patent claims and do not concern the actual principle of this autograph design itself. This had already ceased to be patentable much earlier because it was known.
"After establishing myself here in Baden as a freelance, independent designer several years ago, I continue to develop new instruments, and there is much to say about the latest efforts in the field of modernisation. Indeed, instruments are sufficiently modernised today, and a significant part of the progress made is now common knowledge. Likewise, perceptions regarding intellectual property have been modernised in many places."
Previously, a design, even if it came from a competitor, would still be referred to by the name of the original creator for decades. Nowadays, there is generally little understanding for such subtleties.
A designer worth their salt will never do the same thing twice. The greatest incentive and, at the same time, the greatest encouragement in the field of design comes from competing with oneself.
The latest theodolites (These theodolites are built under licence by the company Kern & Co. in Aarau and can be viewed at the national exhibition.) are available in five accuracy levels, covering the range from simple lightweight construction and travel instruments to fine triangulation theodolites with a 1/2 second direct indication on the measuring drum.
The average reading error ranges from 30 seconds to 1/10 second, approximately in the levels of 30", 3", 1", 1/3", and 1/10". They all share the new vertical axis system, which represents the final elimination of the actual axis. Even with the best cylindrical axis, given the available axis length and the necessary oil film between the axis and the bushing, an effective performance of about three seconds cannot be achieved if the axis is to turn relatively easily.
However, with the new triangulation theodolite, three times greater precision has been achieved. This is an axis system capable of one-second performance. Two surfaces made with exceptional accuracy together with precise balls and a proper ball holder result in a precision ball bearing superior to any other axis form. When proper non-adhesive centreing is also ensured, the horizontal micrometer operates completely free of play.
As the backlash is completely eliminated, the fine crosshair instantly follows the slightest movement of the micrometer screw. Moreover, this arrangement is very insensitive to lubrication and, when executed correctly, is more robust than previous systems with a wasp waist. While I have previously used ball bearings in measuring instruments due to space constraints, these were not intended to increase accuracy and were not executed with the care observed here, providing no indication of the system's performance.
In the two smaller versions, the axis system is similar but naturally smaller.
The conventional tripod screws, which resulted in an instrument tilt of approximately ± 5-6°, have disappeared. Since the new tripods are equipped with a so-called quick or coarse levelling, only a single turn of the three "screws" is now required for instrument levelling.
These "screws" are no longer actual screws but knobs with a horizontal axis and spiral groove. Besides being more compact (they no longer increase the size of the instrument for packaging), the main advantage of this arrangement lies in the elimination of lateral play and backlash.
Combined with the tripod head's coarse levelling, the new setup enables faster readiness for measurement.
In every theodolite, the method of circle reading naturally plays a significant role. Since 1914, it has been established that both telescope positions can be read from the standpoint (without turning) on every instrument. In terms of the fineness of reading, two strongly different levels can be distinguished. One level requires only minimal accuracy but should provide maximum speed and convenience, i.e., the reading must be possible "at a glance." It is now taken for granted that two opposite circle positions are expressed in a single number.
The other level is intended to achieve the maximum accuracy possible for the given instrument size in a simple manner, even if a knob must be turned before reading, i.e., even if the reading takes slightly longer (but not too long).
For the first level, I have applied the coincidence reading with a greatly simplified reading image, i.e., with coarser second division and without a second number series, which results in significantly greater clarity. With the smallest instrument, half or whole minutes (sex. or centesimal) are read in this way, and with the medium-sized instrument, 1/5 or 1/10 minutes sex. or 1/2 minutes centesimal.
Both the smallest and medium-sized instruments are equipped for the second level with a different circle division, and by adding a micrometer, they are configured as second theodolites. For this reading method, the principle of coincidence is no longer applied because, according to my latest research, it does not yield the maximum reading accuracy. In the microscope's field of view, instead of a simple division, a double division is visible; however, each line belongs to the opposite circle position. This double division is read with a micrometer by centering, and the determined number represents the mean of the two circle positions, now 180° apart. While with the coincidence setting, if a line has a local minor damage in a critical location, the reading can be falsified by more than the usual error, with the centering setting, the entire line is used, and minor damages only have a fraction of the effect.
The smallest instrument has circles with a 50 mm division diameter and a microscope magnification of about 20. The first test instrument with a 400 g division, which is in front of me, is divided into 1/5 g; the second drum shows 10 centesimal seconds in size of about 1 mm, allowing individual seconds to be estimated. The medium reading error is approximately 2.7 centesimal seconds, i.e., less than 1" of the old division.
The instrument weighs 2 kg and is probably the smallest one-second theodolite currently in existence. Once a specific instrument type has been designed in a size, an analogous larger version is easily possible. However, when shrinking, it becomes evident that certain construction parts cannot be proportionally reduced, such as screws and especially their control knobs. The spaces between the screw knobs must also not fall below a certain dimension. This results in difficulties in reducing, ultimately determining the smallest possible size. Usually, even with moderate reduction, maintaining exactly the same arrangement as the larger prototype is no longer possible.
Therefore, with this smallest theodolite, the general construction did not cause the main work but rather the disturbance-free arrangement of the various control organs. This instrument has roughly the same accuracy as the previously mentioned 21 cm microscope theodolite from the Dent du Midi (from 1902), but weighs ten times less.
The medium instrument is equipped with 75 mm circles, and its reading error is about three times less, i.e., approximately 1 centesimal second or 0.3" sex., with the same but finer micrometer setup and stronger microscope magnification.
The largest instrument has a net horizontal circle of 100 mm and a vertical circle of 75 mm. The reading accuracy will be approximately 1/10 second (sex.). I cannot provide further details at the moment about the special setup required to achieve this hitherto unattained accuracy, as the construction is currently ongoing. However, it is expected that such an instrument will be exhibited at the national exhibition.
Lastly, there is still something to be said about the telescopes. The first leveling instrument from 1908 had an objective aperture of 27 mm and a magnification of 20. The instrument from 1922, designed for the same level of accuracy, already had an aperture of 40 mm with a 20-fold magnification. The length of the 40 mm telescope was slightly shorter than that of the older 27 mm one. For comparison, the new telescope of the same length (from the medium theodolite) has a free aperture of 45 mm with a 28-fold magnification. With ordinary telescopes, one has reached the limit, as stronger relative reduction makes it impossible to accomplish color correction sufficiently.
Some time ago, I therefore searched for another type of telescope because I needed one for the larger theodolite that matched the other performance increases. This type was found in a combination of lenses with concave mirrors. The new telescope has a free aperture of 75 mm and a sighting height of only 75 mm, so the larger instrument has a lower height than the medium one with a 45 mm objective.
"A universal instrument for astronomical purposes, which I am currently designing, will have a smaller axis height (i.e., measured from the lower edge of the base to the horizontal axis) than the small theodolite from 1922 with only a 40 mm objective aperture, with an aperture of 100 mm and a sighting height of about 100 mm."
The weight of the instrument, once fully packaged, is expected to be less than the weight of the lower part box of the previous 21 cm universal instrument. Therefore, it can be carried by one person. Thus, the limit is reached again for the new type regarding reduction.
The correction of this new telescope is about ten times finer than that of the smaller lens telescopes, i.e., the remaining residual errors, which cannot be eliminated, are only so many hundredths of a millimetre, as compared to the other tenths of a millimetre. Particularly noteworthy is the complete elimination of the secondary spectrum. It is perhaps particularly interesting for Americans that the upright image also fell off, so to speak, as a by-product, without the addition of further optical means, although this caused the telescope length to increase by about a third.
The new instrument designs outlined here are not intended to lead to a reduction in the prescribed tolerances, i.e., the permissible errors of the measurement end results, as the claims in this regard are already partly exaggerated. Instead, they should enable these end results to be obtained more easily, in less time, and with less effort. It should no longer be necessary for the user of an instrument to adjust it before measurement, as measurement methods have long been known that allow for the elimination of possible instrument errors in a simple manner.
"Now that the instruments are sufficiently modernised, it is finally time for the textbooks and manuals of geodesy, etc. (in the broadest sense) to be brought up to the point that corresponds to the current state of technology. I would like to draw attention to just one, but all the more daunting example in this regard. In 1878, the then head of the Prussian survey, General Schreiber, established regulations for the angle measurements of first order triangulations, some of which are still followed today."
These regulations stipulated that on every first-order station, all possible angles between the existing directions had to be measured in certain circle positions. It was the famous "angle measurement in all combinations" to reduce division errors. I examined this method in detail (around 1904) before starting major measurements in the Vaud region, and found that with a certain number of directions and specific, frequently occurring angle sizes, no elimination of division errors occurs that corresponds to the extensive scope of the measurements. Subsequently, this angle measurement was not used in Swiss triangulation. This method requires such a time investment that triangulation in this way costs about twice as much as when proceeding in a more appropriate manner.
The fact that this method was used for a full 60 years, resulting in a large-scale waste of time, is primarily due to the so-called great literature and the instruction of young surveyors influenced by it. The outdated and sometimes inadequate knowledge of instruments conveyed by this literature is also largely responsible for so much valuable time being lost by amateur inventors.
This is not written because increased knowledge of instruments is absolutely necessary for the new instruments, as it is actually the opposite. Formerly, the instruments were impractical, and knowledge of them was often deficient; today, good instruments are available, and even with somewhat deficient knowledge of instruments, a significantly better minimum will be obtained than before. However, the instruments are not meticulously developed so that one obtains a decent minimum with them, but rather so that one enjoys the measurement and takes the slight trouble to become so familiar with one's instrument that one achieves a maximum of accuracy with minimal time and effort.
Baden, March 1, 1939.
Heinrich Wild
