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    Click to enlarge BTCo. The RolCo brand name was registered on 15th September and, like Marconi, Unicorn and other brands, was used for watches at lower price points than the top line Rolex branded watches. The image in Jobin shows a basic grade of this movement with no train jewels but with "Bouchons" "dessus" and "dessous" above and belowthat is brass bushes instead of jewels in the top and bottom plates.

    The RolCo movement is fully jewelled with 15 jewels. Watches with Rolex's "other brands" on their movements such as Marconi, Unicorn or RolCo, are often described as "Rolex watches", but this is not what Rolex would have called them.

    There was often no secret that they were supplied by the Rolex Watch Company, but they were not called or branded Rolex watches, they were called Marconi, Unicorn or RolCo watches by Rolex themselves and if any name appears on the dial it should be the same as the one on the movement. This is discussed in greater detail at Rolex's other brands.

    Back to the top of the page. Click to enlarge Longines Click to enlarge Introduced inthe Longines Often they do not carry the name Longines visibly, but the movements are quite easy to identify. The calibre number If you click on either of the pictures here and get an enlarged view you should be able to see the The shape of the plates and bridges is very distinctive. The 18 jewel movement has the top plate that is most often seen, with individual cocks for the third, fourth and escape wheels.

    This movement does not carry the Longines name, as required by many British retailers. The name is fired into the enamel and Longines told me that the requirement for this dial is recorded in their archives. There is a third variant, the This is a very "English" layout and I am sure that this calibre was created for the British market.

    All variations of the Longines They have a straight line Swiss lever escapement, a cut bimetallic temperature compensation balance with gold timing screws, and a blued carbon steel balance spring with a Breguet overcoil. All parts apart from the visible bridges and cocks are interchangeable between all three variants. The lowest grade The three extra jewels are a jewel bearing for the centre wheel top pivot, and two cap jewels for the escape wheel; the polished steel setting for the top escape wheel cap jewel stands out in the picture.

    The visible train jewels are set in "chatons", metal settings that are fixed in place with small screws. When jewels were first used in the eighteenth century it was found difficult to make the jewel an exact size on its outer diameter with the hole exactly in the centre, so pierced jewels were set into metal settings called that could then be turned so that their outside was the desired diameter and concentric with the hole.

    Early jewels were often made from small pieces of gem stone that had been cut from a larger stone in the process of shaping and polishing it. These small pieces were called "kittens" by the gem cutters, or in French "chatons", which is how these settings came to be called by this name.

    By the time this movement was made the techniques of jewel grinding had advanced and the metal settings were no longer necessary, but they look good and so "top of the range" movements such as the Longines movement in the picture were fitted with them.

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    They were an expensive piece of window dressing that had no effect on the going of the watch, which is why they are only fitted to the visible top holes, the ones the customer sees; the jewels in the bottom holes were rubbed in as usual. Click to enlarge The Longines The savonnette layout was used in hunter cased pocket watches, and for wristwatches. Often movements imported into Britain before the mid to late s do not carry the name manufacturer's name visibly, this was not allowed by British retailers.

    Longines movements are usually quite easy to identify. The calibre number is usually stamped on the bottom plate and is visible next to the escape wheel. If you click on the picture here and get an enlarged view you should be able to see the Be aware that not all movements stamped with this trademark are Longines, Baume also imported watch from other makers.

    It has a straight line Swiss lever escapement, a cut bimetallic temperature compensation balance with gold timing screws, and a blued carbon steel balance spring.

    The balance spring is flat, without an overcoil. Longines movements imported into Britain were customised to suit British tastes. In addition to the absence of a maker's name, the plates are gilded and the screws blued to a purplish colour favoured by Longines.

    These finishes were traditionally used by the best English watchmakers and added to the cost.

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    They were not used in other markets, for which Longines used the standard Swiss finish of nickel plating and polished screws. As far as I can make out, all Longines movements imported into Britain were fully jewelled with 15 or more jewels, for other markets sometimes fewer jewels, e.

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    All these features, cut bimetallic temperature compensation balance with gold timing screws, gilded plates, blued screws, full jewelling and an overall high level of finish, show that Longines was making watches intended for the top end of the British market.

    In nineteenth century Britain, English watches were regarded as the best in the world and Swiss watches had a reputation as being basic and cheap. Longines were countering this by making watches of a quality that anyone would be proud to show off to their friends.

    Click image to enlarge This is the movement I have found most frequently in my collection of Borgel wristwatches. Electa was a division of Gallet. Electa Savonnette Movement 15 Jewels. Click image to enlarge The first movement shown here is a savonnette layout with the small seconds on the dial at 6 o'clock. It has 15 jewels, a split bi-metallic temperature compensated balance and Breguet overcoil balance spring.

    In addition to the 15 jewel type, there was also a higher grade 17 jewel version with the jewels set in chatons, with Reed's whiplash regulator adjuster with swan neck spring for precise adjustment of the regulator lever. The swan neck springs of the Reed adjuster of these movements are often broken. I am planning to make some of these swan neck springs to replace the ones that are missing from my movements - I don't expect that it will be a quick or easy exercise.

    I also have an indirect centre seconds version of this movement, with the seconds hand driven off the arbor of the third wheel by multiplier gearing. This is the bottom picture to the right.

    A full explanation of the working of the centre seconds of this watch is given on the Watch Movements page. This movement was also available with "negative set" or "American system" keyless work. Click image to enlarge. Electa Negative Set When a negative set mechanism is present a setting lever screw, which normally releases the stem, is not fitted, as you can see in the picture to the left. To remove the movement from the case, there is no need to undo the setting lever screw as you would do for a positive set movement, just pull the crown out to the hand set position and the movement can be removed from the case by tilting it slightly.

    Electa Catalogue Confirmation that these are indeed Electa movements was provided to me by David R. The red rubies seem to be rather expensive, presumably they were natural gem stones rather than synthetic. You can read more about Electa and Gallet on my Gallet and Electa page.

    Click image to enlarge The picture to the left shows an Electa movement from a Borgel pocket watch. The fourth wheel arbor, which carries the seconds hand, is pivoted in the cock at the bottom of the picture, the one with "17 jewels" written on it. This is directly in line with the winding stem, which enters the movement at the top. Electa Savonnette Movement Click image to enlarge It is a high quality movement, jewelled to the centre with 17 jewels, four set in chatons as you can see in the picture.

    It has a Reed's whiplash regulator adjuster with swan neck spring for precise adjustment of the regulator lever. I often wonder exactly how they did this, the stripes must have been made with all the cocks and bridges assembled on the bottom plate before the parts were nickel plated. The picture to the right shows a savonnette version of this movement. The similarity between the two movements is striking although they are quite different layouts. The barrel bridge is completely different because the crown wheel and ratchet wheels are transposed.

    Close examination shows that this results in the centre bridge being completely different too, although at first sight it looks very similar. The similarities between the two movements have allowed economies in manufacture to be made. The layout and positioning of the train wheels is identical in the two movements, and the fourth wheel cock, the escape wheel cock and the balance cock are all identical.

    The use of an identical layout for the train means that the wheels and arbors in the two different styles of movement are the same. These movements were the ideal size for a wristwatch.

    The picture to the right shows this, and if you click on it you will get a larger version in a pop-up window which is clearer. Both of these movements are from Borgel wristwatches and so don't have long stems, but I have indicated where the stem is located. When a calibre 63 is used for a wristwatch the small seconds would be at 9 o'clock, so the small seconds are usually omitted in this configuration; the calibre 64 was used when small seconds were required.

    IWC Calibres 63 and In this application they are made pin-set, that is they use a separate push piece to put the keyless work into the hand setting position, so were ideally suited to the Borgel case with its split stem which allowed the movement to screw into and unscrew from the case.

    I first identified the movement pictured as an IWC calibre 64 by comparing the shapes of the plates and bridges with diagrams in IWC " Fournitures" catalogues, and the IWC museum have since confirmed that it is a genuine IWC calibre 64 movement listed in their records.

    However, because it was supplied to Stauffer as a bare movement, IWC will not issue an "extract from the archives" for the watch as they did not supply the case. Stauffer Branded Eterna Movements Eterna cal.

    Eterna with Stauffer trademarks. Click image to enlarge Thanks to Marc for the picture The movement shown here is a customised version of the Eterna calibre movement with none standard bridge shapes. It seems likely that Stauffer asked for these changes to be made so that the movement appeared to be unique to them and not be easily recognised as an Eterna calibre.

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    These bridge shapes were also used for other calibres that Eterna supplied to Stauffer, including a version of the Eterna calibre.

    I also have an 18 ligne pocket watch movement with the same bridge shapes that I have also identified as an Eterna from the keyless works. The vast majority of the components, including the bottom plate, remained exactly the same, but by changing the shape of the bridges and cocks while still leaving all the pivot holes in the same places, a movement could be given a very different appearance.

    The setting lever cover plate and spring detent remain the same for all versions of the Eterna calibre and are the "fingerprint" of the movement. In the picture showing the keyless work I have included the footprint picture of the Eterna from a Bestfit catalogue.

    At least some, perhaps all, of the Eterna movements supplied to Stauffer have the Stauffer ram logo doing under the barrel bridge as shown in the third picture here. This was a registered trademark belonging to Stauffer and so they could insist that it was applied to any movements that were supplied to them, just as they did with IWC.

    Does this mean that there was any connection between Eterna and IWC? No, other than that they both supplied movements or watches to Stauffer.
    Relative dating Studies of stratathe layering of rocks and earth, gave naturalists an appreciation that Earth may have been through many changes during its existence. These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer.

    Lomonosov's ideas were mostly speculative. In the Comte du Buffon tried to obtain a value for the age of Earth using an experiment: He created a small globe that resembled Earth in composition and then measured its rate of cooling. This led him to estimate that Earth was about 75, years old. Other naturalists used these hypotheses to construct a history of Earththough their timelines were inexact as they did not know how long it took to lay down stratigraphic layers.

    This was a challenge to the traditional view, which saw the history of Earth as static,[ citation needed ] with changes brought about by intermittent catastrophes.

    Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform. His calculations did not account for heat produced via radioactive decay a process then unknown to science or, more significantly, convection inside the Earth, which allows more heat to escape from the interior to warm rocks near the surface.

    For biologists, even million years seemed much too short to be plausible. In Darwin's theory of evolutionthe process of random heritable variation with cumulative selection requires great durations of time. According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3. Huxleyattacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions.

    The physicist Hermann von Helmholtz in and astronomer Simon Newcomb in contributed their own calculations of 22 and 18 million years respectively to the debate: However, they assumed that the Sun was only glowing from the heat of its gravitational contraction.

    The process of solar nuclear fusion was not yet known to science. In John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity. Charles Darwin 's son, the astronomer George H. Darwinproposed that Earth and Moon had broken apart in their early days when they were both molten.

    He calculated the amount of time it would have taken for tidal friction to give Earth its current hour day. His value of 56 million years added additional evidence that Thomson was on the right track.

    Radiometric dating Overview By their chemical nature, rock minerals contain certain elements and not others; but in rocks containing radioactive isotopes, the process of radioactive decay generates exotic elements over time. By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated. Convective mantle and radioactivity InThomson had been made Lord Kelvin in appreciation of his many scientific accomplishments.

    Kelvin calculated the age of the Earth by using thermal gradientsand he arrived at an estimate of about million years. InJohn Perry produced an age-of-Earth estimate of 2 to 3 billion years using a model of a convective mantle and thin crust. The discovery of radioactivity introduced another factor in the calculation.

    After Henri Becquerel 's initial discovery inMarie and Pierre Curie discovered the radioactive elements polonium and radium in ; and inPierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour. Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth.

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    These had assumed that the original heat of the Earth and Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished.

    George Darwin and John Joly were the first to point this out, in Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. October Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating.

    Ernest Rutherford in Ernest Rutherford and Frederick Soddy jointly had continued their work on radioactive materials and concluded that radioactivity was due to a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma radiation in the process.

    They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. This rate is given in terms of a " half-life ", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product". Some radioactive materials have short half-lives; some have long half-lives. Uranium and thorium have long half-lives, and so persist in Earth's crust, but radioactive elements with short half-lives have generally disappeared.

    This suggested that it might be possible to measure the age of Earth by determining the relative proportions of radioactive materials in geological samples. In reality, radioactive elements do not always decay into nonradioactive "stable" elements directly, instead, decaying into other radioactive elements that have their own half-lives and so on, until they reach a stable element.

    These " decay chains ", such as the uranium-radium and thorium series, were known within a few years of the discovery of radioactivity and provided a basis for constructing techniques of radiometric dating. The pioneers of radioactivity were chemist Bertram B. Boltwood and the energetic Rutherford. Boltwood had conducted studies of radioactive materials as a consultant, and when Rutherford lectured at Yale in[29] Boltwood was inspired to describe the relationships between elements in various decay series.

    Late inRutherford took the first step toward radiometric dating by suggesting that the alpha particles released by radioactive decay could be trapped in a rocky material as helium atoms. At the time, Rutherford was only guessing at the relationship between alpha particles and helium atoms, but he would prove the connection four years later.

    Soddy and Sir William Ramsay had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium.

    He dated a rock in his possession to an age of 40 million years by this technique. Rutherford wrote, I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his.

    To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye, and cock a baleful glance at me! Then a sudden inspiration came, and I said, "Lord Kelvin had limited the age of the Earth, provided no new source was discovered.

    That prophetic utterance refers to what we are now considering tonight, radium! Rutherford's scheme was inaccurate, but it was a useful first step. Boltwood focused on the end products of decay series. Inhe suggested that lead was the final stable product of the decay of radium. It was already known that radium was an intermediate product of the decay of uranium.

    Rutherford joined in, outlining a decay process in which radium emitted five alpha particles through various intermediate products to end up with lead, and speculated that the radium-lead decay chain could be used to date rock samples. Boltwood did the legwork, and by the end of had provided dates for 26 separate rock samples, ranging from 92 to million years.

    He did not publish these results, which was fortunate because they were flawed by measurement errors and poor estimates of the half-life of radium.

    Boltwood refined his work and finally published the results in His studies were flawed by the fact that the decay series of thorium was not understood, which led to incorrect results for samples that contained both uranium and thorium.

    However, his calculations were far more accurate than any that had been performed to that time. Refinements in the technique would later give ages for Boltwood's 26 samples of million to 2. Rutherford remained mildly curious about the issue of the age of Earth but did little work on it.

    Robert Strutt tinkered with Rutherford's helium method until and then ceased. However, Strutt's student Arthur Holmes became interested in radiometric dating and continued to work on it after everyone else had given up. Holmes focused on lead dating, because he regarded the helium method as unpromising. He performed measurements on rock samples and concluded in that the oldest a sample from Ceylon was about 1. For example, he assumed that the samples had contained only uranium and no lead when they were formed.

    More important research was published in It showed that elements generally exist in multiple variants with different masses, or " isotopes ". In the s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as " neutrons ".

    In that same year, other research was published establishing the rules for radioactive decay, allowing more precise identification of decay series.

    Many geologists felt these new discoveries made radiometric dating so complicated as to be worthless. His work was generally ignored until the s, though in Joseph Barrella professor of geology at Yale, redrew geological history as it was understood at the time to conform to Holmes's findings in radiometric dating.

    Barrell's research determined that the layers of strata had not all been laid down at the same rate, and so current rates of geological change could not be used to provide accurate timelines of the history of Earth. Holmes published The Age of the Earth, an Introduction to Geological Ideas in in which he presented a range of 1.

    No great push to embrace radiometric dating followed, however, and the die-hards in the geological community stubbornly resisted. They had never cared for attempts by physicists to intrude in their domain, and had successfully ignored them so far. Holmes, being one of the few people on Earth who was trained in radiometric dating techniques, was a committee member, and in fact wrote most of the final report.

    Questions of bias were deflected by the great and exacting detail of the report. It described the methods used, the care with which measurements were made, and their error bars and limitations.

    Techniques for radioactive dating have been tested and fine-tuned on an ongoing basis since the s. Forty or so different dating techniques have been utilized to date, working on a wide variety of materials. Dates for the same sample using these different techniques are in very close agreement on the age of the material.

    The quoted age of Earth is derived, in part, from the Canyon Diablo meteorite for several important reasons and is built upon a modern understanding of cosmochemistry built up over decades of research. Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by plate tectonicsweathering and hydrothermal circulation.

    All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nuclide a species of atom characterised by the number of neutrons and protons an atom contains or an intermediate daughter nuclide may have been partially removed from the sample, which will skew the resulting isotopic date.

    To mitigate this effect it is usual to date several minerals in the same sample, to provide an isochron. Alternatively, more than one dating system may be used on a sample to check the date. Some meteorites are furthermore considered to represent the primitive material from which the accreting solar disk was formed.

    Nevertheless, ancient Archaean lead ores of galena have been used to date the formation of Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead-lead isotope systems on the planet.

    These have returned age dates of 4. Severin ordinary chondrite 1.

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