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Fooled in Blackpool
The last word– WATER EVERYWHERE The Last Word has explained how fish drink. But what about waterdwelling mammals such as dolphins and whales. Do they get thirsty? And if they do, how do they drink?
● Dolphins and whales do not drink. Just as we humans cannot use salt water as our source of water, neither can marine mammals. This is because they would need to ingest more fresh water than the seawater they consume in order to excrete the salt it contains. Much of their water comes from fish and squid, which can contain more than 80 per cent water by mass. They can also obtain water through metabolising fat. In order to reduce their water loss they have similar internal designs to those of desertdwelling mammals, including a long loop of Henle in the kidney nephron. As well as internal adaptations, marine mammals did away with sweat glands to stop any water loss through sweating. Instead, they use their surroundings to cool down. Matthew Tranter Newcastle-under-Lyme Staffordshire, UK
dugongs) eat plants. In such foods salt is as little as one-fifth as concentrated as in seawater because the prey has expended energy to excrete salt. You might say that marine mammals rely on their food to desalinate their water. Even mammalian prey can contribute to this process as they eat low-salt organisms. Interestingly, as they are unable to sweat or increase their water intake dramatically when thirsty, whales and seals are vulnerable to changes, especially increases, in water temperature. In particular, many species have great difficulty crossing the equator, while most are comfortable as close to the poles as foraging will take them. Jon Richfield Somerset West, South Africa
FOOLED IN BLACKPOOL From the top of Blackpool Tower (approximately 150 metres) on the UK’s west coast, can you see the curvature of Earth along the Irish Sea horizon? I thought I could, but my friend disagreed. If I’m wrong, how high would we have needed to be?
● Marine mammals certainly are less prone to thirst than land-dwelling mammals; for one thing, they have no need to sweat. They do not swallow any more salt water than they can help, though. Unlike seabirds and turtles, they lack special salt-excreting glands, so every bit of salt they swallow exacts a penalty. However, whales eat animals, and sirenians (manatees and
● While camped at 6000 metres altitude in Peru in 1962, I and some colleagues asked ourselves this question about the Pacific horizon. We actually only saw the curvature by comparing the horizon (about 277 kilometres away) with a nylon thread stretched tight and level between two ice axes. While standing atop Blackpool Tower, if you sight the seaward horizon over a level, 1-metre straight
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.newscientist.com/lastword.ns (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
edge, which is held 1 metre in front of you, trigonometry shows that the ideal horizon would appear to be almost a millimetre higher at the centre of the straight edge than at the ends. This is a much smaller effect than typical atmospheric distortion which, in effect, means there is no visible curvature. From our camp in Peru, the difference was almost 6 millimetres – easily visible when compared with a
“We could see the curvature of the horizon when we stretched a thread between two ice axes” straight edge. Even so, the curvature was not apparent when simply looking at the horizon. Charles Sawyer Byron Bay, New South Wales, Australia ● As the radius of the Earth is 6373 kilometres, a little trigonometry tells us that if you are at the top of a tower of height h metres, the horizon will be at a distance of approximately (2 × 6373 × h)½ kilometres. For a tower 150 metres high, the horizon will be 44 kilometres away and displaced downwards from a true horizontal line by about 0.39 degrees. If you hold a 1-metre stick horizontally 1 metre in front of you, seemingly touching the horizon at the midpoint of the stick, the ends will appear to be 0.8 millimetres above the horizon. That’s pretty hard to see with the naked eye. Eric Kvaalen La Courneuve, France ● When out in the mid-ocean, up at the top of the main mast, the horizon
is a horizontal line right round the field of view. The higher the mast, the lower the horizon appears to be, but it is still a horizontal line. John Eagle Wilmslow, Cheshire, UK ● The short answer to this question is that the curvature is not obviously visible from anywhere on the Earth’s surface. Pilots of Lockheed U-2 and SR-71 Blackbird aircraft suggest that the Earth’s curvature only becomes clear at an altitude of about 18 kilometres. Indeed, it has been photographed from Concorde cruising at this altitude. The curvature can be inferred at sea level, though. For example, ships disappear over the horizon from the bottom upwards, as if sinking into the sea. Mike Follows Willenhall, West Midlands, UK
THIS WEEK’S QUESTION Snakes alive 2 I was surprised to read in an answer to one of the Last Word’s previous questions that sea snakes don’t live in the Atlantic Ocean. While snorkelling on the north coast of Cuba last September, both my partner and I repeatedly saw what I can only describe as a sea snake – it was thin, about 1 metre long with dark and pale markings. It was swimming among thin sea grass about 3 metres down. The locals didn’t seem at all surprised that we’d seen one, and told us with much mirth that it was poisonous. What did we see? Was it just a land snake that fancied a swim? Darren Darby London, UK
How to Fossilise Your Hamster
The latest collection from New Scientist featuring experiments for armchair scientists Available from booksellers and at www.newscientist.com/hamster
Last Words past and present, plus questions, at www.newscientist.com/lastword
● Dolphins and whales do not drink. Just as we humans cannot use salt water as our source of water, neither can marine mammals. This is because they would need to ingest more fresh water than the seawater they consume in order to excrete the salt it contains. Much of their water comes from fish and squid, which can contain more than 80 per cent water by mass. They can also obtain water through metabolising fat. In order to reduce their water loss they have similar internal designs to those of desertdwelling mammals, including a long loop of Henle in the kidney nephron. As well as internal adaptations, marine mammals did away with sweat glands to stop any water loss through sweating. Instead, they use their surroundings to cool down. Matthew Tranter Newcastle-under-Lyme Staffordshire, UK
dugongs) eat plants. In such foods salt is as little as one-fifth as concentrated as in seawater because the prey has expended energy to excrete salt. You might say that marine mammals rely on their food to desalinate their water. Even mammalian prey can contribute to this process as they eat low-salt organisms. Interestingly, as they are unable to sweat or increase their water intake dramatically when thirsty, whales and seals are vulnerable to changes, especially increases, in water temperature. In particular, many species have great difficulty crossing the equator, while most are comfortable as close to the poles as foraging will take them. Jon Richfield Somerset West, South Africa
FOOLED IN BLACKPOOL From the top of Blackpool Tower (approximately 150 metres) on the UK’s west coast, can you see the curvature of Earth along the Irish Sea horizon? I thought I could, but my friend disagreed. If I’m wrong, how high would we have needed to be?
● Marine mammals certainly are less prone to thirst than land-dwelling mammals; for one thing, they have no need to sweat. They do not swallow any more salt water than they can help, though. Unlike seabirds and turtles, they lack special salt-excreting glands, so every bit of salt they swallow exacts a penalty. However, whales eat animals, and sirenians (manatees and
● While camped at 6000 metres altitude in Peru in 1962, I and some colleagues asked ourselves this question about the Pacific horizon. We actually only saw the curvature by comparing the horizon (about 277 kilometres away) with a nylon thread stretched tight and level between two ice axes. While standing atop Blackpool Tower, if you sight the seaward horizon over a level, 1-metre straight
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.newscientist.com/lastword.ns (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
edge, which is held 1 metre in front of you, trigonometry shows that the ideal horizon would appear to be almost a millimetre higher at the centre of the straight edge than at the ends. This is a much smaller effect than typical atmospheric distortion which, in effect, means there is no visible curvature. From our camp in Peru, the difference was almost 6 millimetres – easily visible when compared with a
“We could see the curvature of the horizon when we stretched a thread between two ice axes” straight edge. Even so, the curvature was not apparent when simply looking at the horizon. Charles Sawyer Byron Bay, New South Wales, Australia ● As the radius of the Earth is 6373 kilometres, a little trigonometry tells us that if you are at the top of a tower of height h metres, the horizon will be at a distance of approximately (2 × 6373 × h)½ kilometres. For a tower 150 metres high, the horizon will be 44 kilometres away and displaced downwards from a true horizontal line by about 0.39 degrees. If you hold a 1-metre stick horizontally 1 metre in front of you, seemingly touching the horizon at the midpoint of the stick, the ends will appear to be 0.8 millimetres above the horizon. That’s pretty hard to see with the naked eye. Eric Kvaalen La Courneuve, France ● When out in the mid-ocean, up at the top of the main mast, the horizon
is a horizontal line right round the field of view. The higher the mast, the lower the horizon appears to be, but it is still a horizontal line. John Eagle Wilmslow, Cheshire, UK ● The short answer to this question is that the curvature is not obviously visible from anywhere on the Earth’s surface. Pilots of Lockheed U-2 and SR-71 Blackbird aircraft suggest that the Earth’s curvature only becomes clear at an altitude of about 18 kilometres. Indeed, it has been photographed from Concorde cruising at this altitude. The curvature can be inferred at sea level, though. For example, ships disappear over the horizon from the bottom upwards, as if sinking into the sea. Mike Follows Willenhall, West Midlands, UK
THIS WEEK’S QUESTION Snakes alive 2 I was surprised to read in an answer to one of the Last Word’s previous questions that sea snakes don’t live in the Atlantic Ocean. While snorkelling on the north coast of Cuba last September, both my partner and I repeatedly saw what I can only describe as a sea snake – it was thin, about 1 metre long with dark and pale markings. It was swimming among thin sea grass about 3 metres down. The locals didn’t seem at all surprised that we’d seen one, and told us with much mirth that it was poisonous. What did we see? Was it just a land snake that fancied a swim? Darren Darby London, UK
How to Fossilise Your Hamster
The latest collection from New Scientist featuring experiments for armchair scientists Available from booksellers and at www.newscientist.com/hamster
Last Words past and present, plus questions, at www.newscientist.com/lastword