HOW ELEPHANTS COMMUNICATE

1. A postdoctoral fellow at Stanford University, O'Connell-Rodwell has come to Namibia's premiere wildlife sanctuary to explore the mysterious and complex world of elephant communication. She and her colleagues are part of a scientific revolution that began nearly two decades ago with the stunning revelation that elephants communicate over long distances using low-frequency sounds, also called infrasounds, that are too deep to be heard by most humans. 
2. As might be expected, the African elephant's ability to sense seismic sound may begin in the ears. The hammer bone of the elephant's inner ear is proportionally very large for a mammal, but typical for animals that use vibrational signals. It may therefore be a sign that elephants can communicate with seismic sounds. Also, the elephant and its relative, the manatee, are unique among mammals in having reverted to a reptilian-like cochlear structure in the inner ear. The cochlea of reptiles facilitates a keen sensitivity to vibrations and may do the same in elephants.
3. But other aspects of elephant anatomy also support that ability. First, then enormous bodies, which allow them to generate low-frequency sounds almost as powerful as those of a jet takeoff, provide ideal frames for receiving ground vibrations and conducting them to the inner ear. Second, the elephant's toe bones rest on a fatty pad that might help focus vibrations from the ground into the bone. Finally, the elephant's enormous brain lies in the cranial cavity behind the eyes in line with the auditory canal. The front of the skull is riddled with sinus cavities that may function as resonating chambers for vibrations from the ground.
4. How the elephants sense these vibrations is still unknown, but O'Connell Rodwell who just earned a graduate degree in entomology at the University of Hawaii at Manoa, suspects the pachyderms are "listening" with their trunks and feet. The trunk may be the most versatile appendage in nature. Its uses include drinking, bathing, smelling, feeding and scratching. Both trunk and feet contain two kinds of pressure-sensitive nerve endings—one that detects infrasonic vibrations and another that responds to vibrations with slightly higher frequencies. For O'Connell-Rodwell, the future of the research is boundless and unpredictable: "Our work is really at the interface of geophysics, neurophysiology and ecology," she says. "We're asking questions that no one has really dealt with before."
5. Scientists have long known that seismic communication is common in small animals, including spiders, scorpions, insects and a number of vertebrate species such as white-lipped frogs, blind mole rats, kangaroo rats and golden moles. They also have found evidence of seismic sensitivity in elephant seals—2-ton marine mammals that are not related to elephants. But O'Connell-Rodwell was the first to suggest that a large land animal also is sending and receiving seismic messages. O'Connell-Rodwell noticed something about the freezing behavior of Etosha's six-ton bulls that reminded her of the tiny insects back in her lab. "I did my masters thesis on seismic communication in planthoppers," she says. "I'd put a male planthopper on a stem and play back a female call, and the male would do the same thing the elephants were doing: He would freeze, then press down on his legs, go forward a little bit, then freeze again. It was just so fascinating to me, and it's what got me to think, maybe there's something else going on other than acoustic communication."
6. Scientists have determined that an elephant's ability to communicate over long distances is essential for its survival, particularly in a place like Etosha, where more than 2,400 savanna elephants range over an area larger than New Jersey. The difficulty of finding a mate in this vast wilderness is compounded by elephant reproductive biology. Females breed only when estrus a period of sexual arousal that occurs every two years and lasts just a few days. "Females in estrus make these very low, long calls that bulls home in on, because it's such a rare event," O'Connell-Rodwell says. These powerful estrus calls carry more than two miles in the air and may be accompanied by long-distance seismic signals, she adds. Breeding herds also use low-frequency vocalizations to warn of predators. Adult bulls and cows have no enemies, except for humans, but young elephants are susceptible to attacks by lions and hyenas. When a predator appears, older members of the herd emit intense warning calls that prompt the rest of the herd to clump together for protection, then flee. In 1994, O'Connell-Rodwell recorded the dramatic cries of a breeding herd threatened by lions at Mushara. "The elephants got really scared, and the matriarch made these very powerful warning calls, and then the herd took off screaming and trumpeting," she recalls. "Since then, every time we've played that particular call at the water hole, we get the same response the elephants take off."
7. Reacting to a warning call played high the air is one thing, but could the elephants detect calls transmitted only through the ground? To find out, the research team in 2002 devised an experiment using electronic equipment that allowed them to send signals through the ground at Mushara. The results  of our 2002 study showed us that elephants do indeed detect warning calls played through the ground," O'Connell-Rodwell observes. "We expected them to clump up into tight groups and leave the area, and that's in fact what they did. But since we only played back one type of call, we couldn't really say whether they were interpreting it correctly. Maybe they thought it was a vehicle or something strange instead of a predator warning."
8. An experiment last year was designed to solve that problem by using three different recordings—the 1994 warning call from Mushara, an anti-predator call recorded by scientist Joyce Poole in Kenya and an artificial warble tone. Although still analyzing data from this experiment, O'Connell-Rodwell is able to make a few preliminary observations: "The data I've seen so far suggest that the elephants were responding like I had expected, when the '94 warning call was played back, they tended to clump together and leave the water hole sooner. But what's really interesting is that the unfamiliar anti-predator call from Kenya also caused them to clump up, get nervous and aggressively rumble—but they didn't necessarily leave. I didn't think it was going to be that clear cut.

MARINE CLOCK

1. It was, as Dava Sobel has described a phenomenon: ‘the greatest scientific problem of the age’. The reality was that in the 18th century no one had ever made a clock that could suffer the great rolling and pitching of a ship and the large changes in temperature whilst still keeping time accurately enough to be of any use. Indeed, most of the scientific community thought such clock an impossibility. Knowing one’s position on the earth requires two very simple but essential coordinates; rather like using a street map where one thinks in terms of how far one is up/down and how far side to side.
2. The longitude is a measure of how far around the world one has come from home and has no naturally occurring base line like the equator. The crew of a given ship was naturally only concerned with how far round they were from their own particular home base. Even when in the middle of the ocean, with no land in sight, knowing this longitude position is very simple in theory. The key to knowing how far around the world you are from home is to know, at that very moment, what time it is back home. A comparison with your local time (easily found by checking the position of the Sun) will then tell you the time difference between you and home, and thus how far round the Earth you are from home.
3. Up until the middle of the 18th century, navigators had been unable to determine their position at sea with accuracy and they faced the huge accidental risks of shipwreck or running out of supplies before reaching then destination. In order to determine longitude, sailors had no choice but to measure the angle between Moon centre and a given star – lunar distance – together with height of both planets using the naval sextant. The sailors also had to calculate the Moon’s position if seen from the centre of Earth. Time corresponding to Greenwich Time was determined using the nautical almanac. Then the difference between the obtained time and local time served for calculation in longitude from Greenwich. The great flaw in this ‘simple’ theory was – how does the sailor know time back home when he is in the middle of an ocean?
4. The obvious and again simple answer is that he takes an accurate clock with him, which he sets to home time before leaving. All he has to do is keep it wound up and running, and he must never reset the hands throughout the voyage. This clock then provides ‘home time’, so if, for example, it is midday on board your ship and your ‘home time’ clock says that at that same moment it is midnight at home, you know immediately there is a twelve hour time-difference and you must be exactly round the other side of the world, 180 degrees of longitude from home.
5. After 1714, when the British government offered the huge sum of £20,000 for a solution to the problem, with the prize to be administered by a board splendidly titled Board of Longitude. The government prize of £20,000 was the highest of three sums on offer for varying degrees of accuracy, the full prize only payable for a method that could find the longitude at sea within half a degree. If the solution was to be by timekeeper (and there were other methods since the prize was offered for any solution to the problem), then the timekeeping required to achieve this goal would have to be within 2.8 seconds a day, a performance considered impossible for any clock at sea and unthinkable for a watch, even under the very best conditions.
6. It was this prize, worth about £2 million today, which inspired the self-taught Yorkshfre carpenter, John Harrison, to attempt a design for a practical marine clock. During the latter part of his early career, he worked with his younger brother James. Their first major project was a revolutionary turret clock for the stables at Brocklesby Park, seat of the Pelham family. The clock was revolutionary because it required no lubrication. 18th century clock oils were uniformly poor and one of the major causes of failure in clocks of the period. Rather than concentrating on improvements to the oil, Harrison designed a clock which didn’t need it. In 1730 Harrison created a description and drawings for a proposed marine clock to compete for the Longitude Prize and went to London seeking financial assistance. He presented his ideas to Edmond Halley, the Astronomer Royal. Halley referred him to George Graham, the country’s foremost clockmaker. He must have been impressed by Harrison, for Graham personally loaned Harrison money to build a model of his marine clock. It took Harrison five years to build Harrison Number One or HI. He demonstrated it to members of the Royal Society who spoke on his behalf to the Board of Longitude. The clock was the first proposal that the Board considered to be worthy of a sea trial in 1736.
7. After several attempts to design a betterment of HI, Harrison believed that the ‘ solution to the longitude problem lay in an entirely different design. H4 is completely different from the other three timekeepers. It looks like a very large pocket watch. Harrison’s son William set sail for the West Indies, with H4, aboard the ship Deptford on 18 November 1761. It was a remarkable achievement but it would be some time before the Board of Longitude was sufficiently satisfied to award Harrison the prize.
8. John Hadley, an English mathematician, developed sextant, who was a competitor of Harrison at that time for the luring prize. A sextant is an instrument used for measuring angles, for example between the sun and the horizon, so that the position of a ship or aeroplane can be calculated. Making this measurement is known as sighting the object, shooting the object, or taking a sight and it is an essential part of celestial navigation. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. A sextant can also be used to measure the lunar distance between the moon and another celestial object (e.g., star, planet) in order to determine Greenwich time which is important because it can then be used to determine the longitude.
9. The majority within this next generation of chronometer pioneers were English, but the story is by no means wholly that of English achievement. One French name, Pierre Le Roy of Paris, stands out as a major presence in the early history of the chronometer. Another great name in the story is that of the Lancastrian, Thomas Earnshaw, a slightly younger contemporary of John Arnold’s. It was Earnshaw who created the final form of chronometer escapement, the spring detent escapement, and finalized the format and the production system for the marine chronometer, making it truly an article of commerce, and a practical means of safer navigation at sea over the next century and half.