Coherent Lodge
In the initial part of the article on why grains might stick together to obstruct a flow (2 August, p 38), there was a reference to the observations made by Edouard Branly in 1890 regarding the reduction in electrical resistance of metal filings exposed to an electrical spark. This does more than a little injustice by failing to mention the work of one of Britain’s greatest 19th-century experimental physicists.
Oliver Lodge had observed, in 1889, that when two metallic surfaces were separated by a minutely small gap, they frequently fused together when an electric spark occurred nearby. During 1891 and 1892 he employed this principle in several different forms to detect radio waves. He observed: “This arrangement, which I will call a ‘coherer’, is the most astonishingly sensitive detector of Hertzian waves.”
When Lodge learned of Branly’s findings in 1893, he recognised their significance immediately. It was another example of his coherer principle. Lodge proceeded to develop it as the first real radio detector. It was used widely (including by Marconi) well into the 20th century. It is perhaps a little unfortunate that it became known as the “Branly coherer”, suggesting that Branly invented both the device and the name.
It is not true that “no one ever got round to explaining the bizarre electrical behaviour of the filings”. Over 100 years ago Lodge provided an explanation for the phenomenon along the lines referred to in the article, namely that the spark induces a radio-frequency electric current in the filings, welding together the points of contact to provide a conducting path for electric currents.
The present findings, at least in the case of metal filings and electric sparks, provide no great improvement on the explanation provided by Lodge.
Frequent forger
In her article about the toad in the hole, Gail Vines suggests that Charles Dawson fabricated the entombed toad as a trial run for his later more spectacular fraud 鈥� Piltdown man (9 August, p 50).
In my last year at secondary school in East Grinstead, Sussex, way back in 1976, I remember that we had a visit from a member of the local antiquities society. He took us out onto the Weald to show us how iron was smelted there in past centuries. In passing, he showed us a reproduction of a brass plaque that commemorated a Wealden iron master and depicted the whole process of smelting iron. He pointed out to us that the depiction was incorrect in almost every detail 鈥� it was in fact a forgery.
And who had “found” this plaque? Charles Dawson.
Letter
While I support the ideals of hydrogen power there is one question that no one has yet been able to answer for me: isn’t the water vapour produced by fuel cells a more effective greenhouse gas than just about everything else? Think of Venus.
James Randerson replies:
鈥� Water vapour does have a potent greenhouse effect, and fuel cell cars emit more water than conventional engines because oxygen is combined with hydrogen only (to make water) rather than hydrogen and carbon (to make water and CO2). However, if that hydrogen came originally from electrolysis of water then using the hydrogen as fuel will not add “new” water to the system. Even “new” water (ultimately from hydrocarbons) will not have a noticeable effect. Currently, the global energy system emits around 20 billion tonnes of water per year 鈭� 0.0038 per cent of the Earth’s annual evaporation.
Time bomb
The appeal found within the MSBlaster worm, which begs Bill Gates to stop making money and fix his software, is a pertinent one (16 August, p 6). At the time when the internet was burgeoning, Microsoft made great play of how easy it was to interact with it using Microsoft software. As an IT professional, I had grave doubts about the wisdom of making the net, in effect, an extension of one’s hard disc.
Over time we have had problem after problem, the MSBlaster worm being merely the latest, because the security of the original Microsoft design is badly flawed. What we are now having to do, retrospectively, is bring in a clear distinction between one’s machine and the rest of the net by use of firewalls and so on. But this is very difficult because the boundary is blurred in the fundamental software. Microsoft does indeed have some questions to answer in this debacle.
Pirating fine art
In your article about piracy and digitised fine art, the issue of works in the public domain was not addressed (9 August, p 8).
I have researched the legal boundaries of using photos of works in the public domain. In the case of Bridgeman Art Library vs Corel Corporation, heard in New York state, Corel compiled a commercial CD-ROM that included some of the Bridgeman library’s photographs of works in the public domain. The Bridgeman sued, claiming that it had the copyright on the photos and that Corel had violated the copyright.
The court ruled in favour of Corel, stating that the images were “slavish” copies of the originals 鈥� meaning that, as producing them involved no creative input, they could not be copyrighted, since they were photos of works in the public domain.
So even if a gallery wanted to copyright its photos of public-domain works in its possession, it couldn’t, unless it injected some creative element. This would not apply to works not in the public domain, of course. Also, if I went to a gallery and took pictures of works in the public domain but added some creative touch, or altered them with a digital editing program, I would retain the copyright on those images.
Illegal fishing
Linda Shields argues that the Australian government should “bring some compassion to fishing laws in its northern waters” (9 August, p 29).
Australia does not imprison Indonesian fishermen for illegal fishing and indeed is prevented from doing so by the United Nations Convention on the Law of the Sea. Illegal fishers are fined or put on a “good behaviour bond” and often a bond is imposed for the release of a seized boat. Where fines are not paid or where repeat offenders breach bonds for previous offences, fishers may serve sentences in Australian prisons. Some boats are destroyed if a bond is not paid, some because they pose quarantine risks or are unseaworthy.
Illegal fishing by Indonesians impacts significantly on Australia’s marine environment. Shark finning 鈥� the inhumane practice of cutting off the fins while the shark is alive 鈥� is banned in Australia and in most parts of the world, and threatens the environmental balance of the region. It has a drastic impact on shark numbers. In addition, some fishers use dolphins as bait to catch sharks.
Australia has a right to protect its exclusive fishing zone under international law, just as Indonesia does. But large areas of Indonesian waters are overfished and this drives many Indonesian skippers into Australia’s waters. So the Australian government is also focusing on preventing illegal fishing by working with Indonesia on projects in their communities, including education and fisheries management, as well as alternatives to fishing as a livelihood.
It is through this mix of enforcement and proactive measures that we hope to find a solution to illegal fishing and reverse the depletion of Indonesia’s own waters.
Let the sunshine in
Celeste Biever’s article was long overdue as part of righting the balance in the debate about the benefits and dangers of sunshine 鈥� but only as far as it went (9 August, p 30). First, what many dermatologists fail to make explicit is that, of the 1650-odd deaths from malignant melanoma in the UK each year, more than half are caused by hazards other than solar radiation.
Second, the specific UV frequency required for photosynthesis of vitamin D is UVB. Most sunscreens block UVB completely. Natural alternatives should be investigated for both their protective properties and minimum interference with vitamin D photosynthesis.
Third, research also links exposure to sunlight with lower rates of heart disease, diabetes, MS and depression. Adding this to its preventive effects on many cancers and osteoporosis, the strong picture emerges that the benefits of sensible sun exposure far, far outweigh the hazards.
The missing variable seems to be nutrition. Many of the leading heliotherapists who treated TB, rickets and smallpox with UV in the 1930s and 1940s warned against sunbathing on a high-fat diet. It is time the medical profession focused on understanding the many benefits of sunlight, along with the nutritional factors that predispose people to, or protect them from, UV risk, rather than being led astray by unbalanced public risk campaigns influenced by commercial interests.
False alarm?
Your report on gamma-ray weapons raises concerns that may be premature (16 August, p 4). A group of us, using the Advanced Photon Source at Argonne, have tried to reproduce the “isomer triggering” effect reported by Carl Collins and colleagues. Our X-ray beam was vastly more intense, so we should have seen an overwhelming signal. We saw none.
If the enormous X-ray flux from a synchrotron light source cannot trigger the decay, then perhaps there need not be concern about a new arms race. The essence of the scientific method is reproducibility. The discovery of fission in 1938 was confirmed at a number of laboratories within a few months. The “triggered decay” of the hafnium isomer was first reported 4 years ago and, so far, has been reproduced only by various combinations of the original authors.
Hydrogen hype
A dangerous myth is in the process of taking root in regard to hydrogen power (16 August, p 3 and p 8). It claims that in a few years’ time the hydrogen economy will save us from the twin horrors of dwindling oil reserves and global warming. Once we have overcome a few technical problems concerning storage and fuel cell cost, the future will be rosy.
The danger is that this approach breeds a business- as-usual complacency and blinds us to the real issue, which is how much energy we need to sustain our present existence.
Consider the statistic you cite: “If the entire US fleet of 200 million vehicles converted to fuel cells and plugged in, they would generate four times the grid’s current capacity.” Turn this on its head and it looks rather different: “We will need four times the current national grid capacity to make the hydrogen required to run all the cars in the country.”
Granted, the nation’s cars won’t all be on the road at the same time, but taking into account conversion efficiencies, national generating capacity would probably have to double just to feed our cars. That’s a lot of windmills.