How did it begin? When did electricians come with a bright idea to electrify oceanographic measurements? The answer lies deep in the ocean with the first three failed attempts to lay a telegraph cable between Europe and America in the mid-19th century.
Electricians asked naturalists and physicists why their cables break, why the resistance of cables changes at depth, what are the properties of ocean water at depth – and did not get complete answers about what affects submarine cables, what happens to them at the bottom of the ocean.
This fact is not very well known, and it is a particularly interesting story for finding roots in the development of electronic devices in Oceanography and the challenges it faced at the age of “glass and brass” oceanographic instruments.
During the famous Challenger Expedition 1872-76, which is noted as the beginning of Oceanography as a Science, there was a request from the telegraph companies and investors to light up the dark secrets of the ocean and provide them with a detailed map of depths and temperature of the oceans. To fulfill their request for more detailed temperature profiles, they even provided a special thermometer aboard the HMS “Challenger”.
It was a complete deep-sea electrical thermometric system, a gift from Sir William Siemens, which he designed on the principle of the variation of the electrical resistance of a conductor with its temperature. Sir Charles William (Carl Wilhelm) Siemens was a great German-British electrical engineer and businessman.
In 1850 he established the London sales office of Siemens & Halske, the engineering company producing telegraphs, which his brother Werner had founded in 1847 at Berlin. He started selling such devices to the wire rope producer Newall&Co, which soon outsourced test jobs for cables to Siemens and that enabled the new company to enter the ocean cable-laying business. Sir C.W. Siemens pursued two major themes in his inventive efforts, one based upon the science of heat, the other based upon the science of electricity; and the electric thermometer was, as it were, a delicate cross-coupling that connected both. In the Bakerian Lecture for 1871 “On the Increase of Electrical Resistance in Conductors with Rise of Temperature”, he showed that this principle might be applied to the construction of an electrical thermometer, which would be of use in cases where a mercurial thermometer was not available. He devised an instrument for measurement temperatures where the greatest degree of accuracy is required, as in the case of deep-sea observations.
It employed a simple bridge circuit with null indicated by a marine galvanometer of the type invented for cable laying by Sir William Thompson some twenty years earlier. The measuring transducer, a 15mm diameter coil of silk-covered metal wire with 432 Ohm resistance provided with three leads to compensate for cable resistance. The electrical balance was attained by a method truly beautiful for its certainty and simplicity. The reference coil (S) was merely put into a water bath along with hot and cold water in the proportions required to balance the galvanometer (G).
A good mercury-in-glass thermometer then indicated the reference temperature for calibration of the measuring system. It was an elegant experimental method limited hardly at all as to precision, certainly not by “contact resistance”. As it was stated in the Challenger Report: “Only the briefest of tests of Sir Siemens ‘ gift was carried out during the expedition even though it apparently was capable of very fine measurements. Its design was sensible and conservative”.
Why did this prototype not start a tradition long ago, leading to routine electrical wire hydrographic casting?
The “electricians” were at that time quite prominent in natural philosophy and were the ones who first floundered out to sea with machinery to lay cables. Seems like something missing in this story. Perhaps something was found to be incompatible with some feature of the work at sea, for example, needs in a cooling system, a low capacity of batteries, or maybe it was just poor cable insulation. I would also suspect the lack of practical experience in electrical engineering of Challenger’s Lieutenants. They were in charge of temperature measurement in the expedition, but were not familiar with handling electric network and had no personal scientific interest in testing Seimens’ thermometer, rather put effort into extensive testing of Negretti-Zambra mercury reversing thermometers, also for the first time taken in the expedition and extensively used during soundings. “No permanent place was fitted for galvanometer or apparatus, and in consequence continuous and careful observations were not made”.
Later, the Siemens brothers developed a generator to replace the original batteries and added an ice-machine for providing chilled water for the control tank.
During the autumn of 1881 Siemen’s electrical thermometer was successfully tested in the Gulf Stream onboard U.S.S “Blake” by Commander Bartlett, to show its entire practicability.
A series of observations were taken using Miller-Casella thermometers immediately prior to the Siemens’ measurements. Five minutes were allowed for the coil to assume the ambient temperature, and after balancing the bridge, another 5 minutes were allowed to elapse to ensure the stability of both coils. In the majority of cases the results were identical to those made by the Miller-Casella thermometers.
In 1882 Sir C.W.Siemens published in the Processings of the Royal Society a paper “On a Deep Sea Electrical Thermometer”, in which he presented his thermometer and summarized results of seagoing trials of his invention. Very important reasoning of the advantage of the electrical thermometer was done for the specific conditions of comparison in a layer of 30-50 fathoms, where the temperature inversion resulted in large errors for the Miller-Casella mercury thermometers, based on the indication of minimum temperature: “The two instruments gave precisely the same readings at positions of maximum or minimum temperature, but that in intermediate positions the electrical thermometer, in almost every instance, gave a higher reading. This discrepancy may be accounted for, I think, by the circumstance that the electrical thermometer gives the temperature of the water actually surrounding the coil at the moment of observation, whereas the reading of the Miller-Casella instrument must be affected by the maximum or minimum temperatures encountered in its ascent or descent, which may not coincide with that at the points of stoppage.”
The final conclusion followed: “A strong argument in favour of the electrical instrument for geodetic and meteorological purposes has thus been furnished.”
It is hard to tell why it happened because the records of mild successes soon become dim for many years ahead. ” When accurate temperature observations are required from the intermediate depths, this instrument is especially valuable, and it will in all probability be intensively used in future deep-sea investigations.” . In fact, by this time such observations could be more speedily and conveniently carried out with several reversing thermometers spaced along the single sounding line, thus avoiding the need for ice-machines, galvanometers or the ship’s being hove-to with engines stopped for several hours.
In 1874 Siemens designed the cable ship Faraday and assisted in the laying of the first of several transatlantic cables that it completed. C.S. Faraday spent the next 50 years laying an estimated total of 50,000 nautical miles (93,000 km) of cable for Siemens Brothers. On this ship, the Siemen’s electrical thermometer was also in use to measure the temperature of cables.
There was another invention of Sir William Siemens in the field of hydrography instrumentation. In 1876 he demonstrated how to register the depth of water beneath a ship’s keel without putting any apparatus into the water. The apparatus was in fact a gravimeter, consisted of a tube of mercury delicately suspended, with a set of electrical contacts at the base. Any diminution in gravity equal to 1/370000, which represented about 10 fathoms (18m), should result in a proportional lowering in the height of mercury, in this case, 1.62um. With the addition of a micrometre screw, Siemens claimed to be able to detect changes in water depth accurately to 1 fathom (1.8m).
Although he made calculations to take into account those factors which modify the force of gravity at the Earth’s surface – temperature, atmospheric pressure, latitude and the nature of rocks below – Siemens never got good results with this bathometer. He tried it out on C.S. Faraday in the North Sea and later in the North Atlantic, and obtained figures usually greater than those given simultaneously with a Thompson sounding machine(5).
During the last fifteen years of his life, he actively supported the development of the engineering profession and its societies. Remarkable, that the derived SI unit of electrical conductance Siemens (S) is named after brothers Siemens. It is used in measuring conductivity, where the derived unit is S/m.
- “Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873-76.” Vol.1. Physics and Chemistry, Prepared by Sir C.Wyville Thomson, John Murrey, 1884.
- “On determining the Depth of the Sea without the use the Sounding-line“, by C.William Siemens, Received January 20, 1876, Phil. Trans.
- “On a Deep Sea Electrical Thermometer.” By C. William Siemens, Received June 7, 1882, Proc. Roy. Soc., vol. 19.
- “Sir Charles William Siemens” by Robert H. Thurston, Science, Vol. 3, No. 49, Jan. 11, 1884.
- “No Sea Too Deep”, by A. McConnell, 1982