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Josiah Latimer Clark was an electrical engineer. He participated in the development of wireless telegraphy, particularly, Anglo-American trans-Atlantic cable. He developed famous"Clark cell” - a stadard electrochemical cell, made some standard electrical measurements collected in tables and headed a company producing electrical and electronic instrument and devices.
Josiah Clark was born at Great Marlow in 1822, and probably acquired his scientific bent while engaged at a manufacturing chemist’s business in Dublin. However, most of the time, Josiah Clark was more of a civil and electrical engineer than a chemist. On the outbreak of the railway mania in 1845 he took to surveying, and through his brother, Mr. Edwin Clark, became assistant engineer to the late Robert Stephenson on the Britannia Bridge. While thus employed, he made the acquaintance of Mr. Ricardo, founder of the Electric Telegraph Company, and joined that Company as an engineer in 1850.
He rose to be chief engineer in 1854, and held the post till 1861, when he entered into a partnership with Mr. Charles T. Bright. Prior to this, he had made several original researches; in 1853, he found that the retardation of current on insulated wires was independent of the strength of current, and his experiments formed the subject of a Friday evening lecture by Faraday at the Royal Institution - a sufficient mark of their importance.
One of the most memorable of Clark’s achievements was to patent a pneumatic system for the transport of letters and parcels. Pneumatic (air powered) capsule pipelines were invented by George Medhurst in 1810. He originally thought they would be used to transport people who would travel in capsules as large as railway carriages.
He decided that people would not like travelling inside pipes and invented ‘atmospheric’ railways instead. Josiah Latimer Clark popularized pneumatic system use as an adjunct to the overloaded Victorian telegraph system. In 1840s London, the volume of short-distance telegraph messages grew so great that the Morse code operators couldn’t keep up. Clark’s solution was to build an underground tube system that would send hollow cylinders filled with message slips. These earliest versions of pneumatic tubes were powered by steam engines that created a vacuum to suck the carriers along.
The first half of the 19th century saw an unprecedented acceleration of communication through the introduction of the electric telegraph. Its principal application was to commercial intelligence for the merchants on the stock exchanges for whom fortunes could be won by the receipt of advance information, but the gain in speed from the telegraph could be lost if a message took a long time to get from the telegraph office to the stock exchange.
It was to avoid this delay that in 1853 J. Latimer Clark installed a 220 yard long pneumatic tube (1.5 inch diameter) connecting the London Stock Exchange in Threadneedle Street with the Central Station in Lothbury of the Electric Telegraph Company which had been incorporated in 1846. A steam engine was used. Cyllindrical message carriers moved with the speed of 20 feet/sec. There were similar installations in Berlin in 1865 between the Central Telegraph Office and the Stock Exchange, and in 1866 in Paris out of the place de la Bourse.
Engineers J. Latimer Clark and T. W. Rammell formed the Pneumatic Despatch Company, which built a demonstration tube above ground in Battersea in 1861. This line successfully carried loads up to 3 tons… and even a few passengers, lying down in the vehicles in the 30-inch pipe! With the large pipe and small vehicles, a much lower pressure could be used, no more than 0.025 atmosphere.
Vehicles ran on a 2-foot gauge track formed right into the tube segments, and speeds up to 40 mph were reached. The Pneumatic Dispatch Railway, as it became known, operated until 1874, but at this point the Post Office decided that the time saving wasn’t worth the cost.
In both telegraphy and power engineering, field tests were often done to examine, for example, cable insulation. Some few field experiments had however been designed for purposes other than testing. These experiments were not performed in the laboratory precisely because the reduction in scale would not result in the anticipated effect.
Latimer Clark and Michael Faraday’s large-scale experiment on the effect of dielectric insulation upon signal retardation in submarine telegraphy provides an apposite example. In one of these experiments, Clark and Faraday used eight 200-mile telegraphy lines between London and Manchester, for a total of 1,600 miles. The lines were connected in such a way that all measurements could be made at London, instead of at both London and Manchester.
This requirement was critical because it permitted local, laboratory control without losing the large scale effect that would have disappeared had it been performed with test cables at Faraday’s Royal Institution laboratory. The Lothbury Telegraph Office, where the measurements were made, was thereby transformed into a superb laboratory.
In 1856 Josiah Latimer Clark invented and patented the well-known"double-bell” insulators for telegraph wires and he formed a company which was involved in manufacturing and laying over 100,000 miles of submarine cables all over the globe.
In 1858, he and Mr. Bright produced the material known as"Clark’s Compound", which is so valuable for protecting submarine cables from rusting in the sea-water. In 1859, Mr. Clark was appointed engineer to the Atlantic Telegraph Company which tried to lay an Anglo-American cable in 1865. In partnership with Sir C. T. Bright, who had taken part in the first Atlantic cable expedition, Mr. Clark laid a cable for the Indian Government in the Red Sea, in order to establish a telegraph to India. In 1886, the partnership ceased; but, in 1869, Mr Clark went out to the Persian Gulf to lay a second cable there. Here he was nearly lost in the shipwreck of the Carnatic on the Island of Shadwan in the Red Sea.
Subsequently Mr. Clark became the head of a firm of consulting electricians, well known under the title of Clark, Forde and Company, and latterly including the late Mr. C. Hockin and Mr. Herbert Taylor.
The Mediterranean cable to India, the East Indian Archipelago cable to Australia, the Brazilian Atlantic cables were all laid under the supervision of this firm. Mr. Clark is now in partnership with Mr. Stanfield, and is the joint-inventor of Clark and Stanfield’s circular floating dock.
Mr. Clark was also head of the well-known firm of electrical manufacturers, Messrs. Latimer Clark, Muirhead and Co., of Regency Street, Westminster.
Mr. Clark was an engineer of various and even brilliant gifts. Mr. Clark has applied himself in divers directions, and never applied himself in vain. There is always some practical result to show which will be useful to others. In technical literature he published a description of the Conway and Britannia Tubular Bridges as long ago as 1849.
There is a valuable communication of his in the Board of Trade Blue Rook on Submarine Cables. In 1868, he issued a useful work on ELECTRICAL MEASUREMENTS, and in 1871 joined with Mr. Robert Sabine in producing the well-known ELECTRICAL TABLES AND FORMULAE, a work which was for a long time the electrician’s VADE-MECUM. In 1873, he communicated a lengthy paper on the NEW STANDARD OF ELECTROMOTIVE POWER now known as CLARK’S STANDARD CELL; and quite recently he published a treatise on the USE OF THE TRANSIT INSTRUMENT.
In calibrations with the potentiometer it is necessary to have a"normal” or"standard” cell of known and constant e.m.f. The two cells used universally for this purpose are the cells devised by Latimer Clark and by Edward Weston. In 1872 Latimer Clark invented the"Clark Cell". It consisted of mercury and zinc amalgam electrodes in a saturated solution of zinc sulfate.
This was a big improvement over the Daniell Cell, but suffered from two major imperfections. It had a large temperature coefficient of -0.00115 V/°C, and suffered from cracking where the platinum connections entered the glass envelope. This was caused by the platinum alloying with the zinc amalgam. In spite of its problems, it was reproducible, and became the first commercially successful standard cell.
A form of the Clark cell is shown in this figure. The positive pole is mercury (Hg), in contact with a paste of mercurous sulphate (Hg2SO4), and the negative pole is zinc amalgame in contact with a saturated solution of zinc sulphate.
Lord Rayleigh investigated a form of the Clark Cell in 1885 that became known as the Board of Trade Cell of 1894. He established the e.m.f. at any temperature to be:
Et = E15 (1 - 0.00077(t - 15))
He gave the voltage as 1.434 volts at 15° C, but subsequent investigation has shown this value to be too high by nearly 0.1%. An improved form of the cell was developed at the Reichsanstalt, by Kahle. The correct e.m.f. is 1.4328 international volts, according to Laws Electrical Measurements (1917).
Clark’s transit telescope
Latimer Clark, the designer of this transit telescope, desired"to introduce the transit instrument into more common use for purposes of utility and amusement, and more especially as a means of obtaining true time for the regulation of clocks and watches. Those who have seen the numbers who daily attend the well-known horological establishments in London, for the purpose of comparing their watches with a standard, will readily admit that an easy means of obtaining accurate time is not only a matter of great public utility, but has become an existing want".
He added wishfully,"if this charming instrument were more fully known it would become as popular as the stereoscope or camera". Clark considered that"many a lover of nature will find immense pleasure in watching the exquisite precision of the movements of the heavenly bodies” and he wrote an explanatory work in 1882 for those"who would never dream of opening a book on Astronomy but who may desire to use a transit instrument as they would use a telephone, without necessarily caring to study the principles of its construction".
Giving an introduction to the owner, Clark continued:"The instrument is adjusted quietly by the fireside, and when the time approaches he lays the telescope in its stand and looks through it, and at the proper moment he sees the one star he is seeking pass the cross wires and give him his time to a fraction of a second. This operation is, in fact, so easy that his gardener or coachman may be taught to use the instrument in his absence almost as accurately as himself".
The Latimer Clark-pattern stereoscopic camera was designed to use wet collodion plates and has only one lens. In order to obtain the two negatives it was necessary to move the camera from left to right between exposures and then push across the plate holder prior to exposure of the second image.
Mr. Clark was a Fellow of the Royal Society of London, as well as a member of the Institution of Civil Engineers, the Royal Astronomical Society, the Physical Society, etc., and was elected fourth President of the Society of Telegraph Engineers and of Electricians, now the Institution of Electrical Engineers.
The notion volt was introduced by Josiah Latimer Clark. Volt is a unit of electrical potential, potential difference and electromotive force in the metre-kilogram-second system (SI); it is equal to the difference in potential between two points in a conductor carrying one ampere current when the power dissipated between the points is one watt. An equivalent is the potential difference across a resistance of one ohm when one ampere is flowing through it. The volt is named in honour of the 18th-19th-century Italian physicist Alessandro Volta. These units are defined in accordance with Ohm’s law, that resistance equals the ratio of potential to current, and the respective units of ohm, volt, and ampere are used universally for expressing electrical quantities.
He was a great lover of books and gardening - two antithetical hobbies - which are charming in themselves, and healthily counteractive. The rich and splendid library of electrical works which he was forming, has been munificently presented to the Institution of Electrical Engineers.
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