Letters to the Editor
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Light on sprites
Might the mysterious “sprites” seen high above some thunderstorms (“Bolts from the blue”, 19 August) be connected with the ionospheric phenomenon known as sporadic E? This consists of drifting, cloud-like patches of intense ionisation with a lifetime of a few hours, which are detectable because of the enhanced range they provide for VHF radio. Their source has long been a mystery, although I believe that thunderstorms have been suggested.
On the subject of thunderstorms, I wonder if any of your readers have seen a rather odd effect that I noticed some years ago. A streak of lightning seemed to break up into a regular “string of beads”. I would guess that there were around a hundred of them, evenly distributed along the length of the streak. I don’t think that it was a dazzle effect, as the streak wasn’t very vivid. I would be interested to know whether this is a known phenomenon, and if so, whether any explanation has been offered.
Boom, hiss
I have also used the “white noise” method to blot out noisy neighbours, but in my experience the elaborate installation described by Andrew Chester is not necessary (Letters, 26 August).
If you have an FM radio or a TV in your room, simply tune it away from a station and turn up the volume in order to silence intrusive noise from any source. The brain soon ignores the “hiss” as it contains no information, but as the ear’s response to sound is logarithmic, the nuisance noise appears to get much quieter.
The method enables you to get to sleep even at quite high nuisance noise levels, and I have even made it work in a hotel room. The only thing to watch out for is that the TV or radio is not on the edge of a station’s frequency range, as you will hear the odd snatch of music or speech which is guaranteed to keep you awake.
Current affairs (1)
David Milsted makes a common mistake in his article about mistakes made by geniuses (Forum, 19 August). He says that, thanks to Lord Kelvin, “the official residences of Britain’s Royal Family were until quite recently powered by the much more dangerous direct current”.
Ripple-free DC, such as is obtained from a battery or well smoothed power supply unit, is less dangerous than alternating current at 50 or 60 hertz. A constant direct current of two to four times the 50 hertz current is required to produce the same excitatory effects on the human body. The power frequencies in normal use are the worst in terms of the effects on the body.
The threshold of perception at 50 to 60 hertz AC is about 0.5 milliamps. However, the threshold of perception of DC is typically 2.0 milliamps.
I have found that the majority of people think that DC is more dangerous than AC. One possible reason for this is that it is more difficult to interrupt DC than AC and when DC is interrupted there is a much larger discharge arc than for the same current at 50 hertz AC.
We done good
Martin Dawson states that “for at least the next ten years in Europe, there will be more emissions from cars without [catalytic] converters than from newer cars” (Letters, 12 August). Put another way, the few pre-1993 cars still on the road in 2005 will generate more pollution than all those produced between 1993 and 2005.
That is a welcome (and unsolicited) testimonial to the effectiveness of the investment made by the oil and motor industries in dramatically reducing pollution from new vehicles. As a result, air quality is improving, and this will continue into the next century.
These improvements are across the full range of transport pollutants. Adding oxygenates, on the other hand, tackles carbon monoxide, but does little or nothing to reduce other pollutants. They may also, as you said, increase some emissions (“Are oxyfuels good for us?”, 15 July).
Oxygenates have been made mandatory in some American cities where carbon monoxide is a severe problem. Because of our different climate, carbon monoxide does not pose such a serious threat in Britain. In 1993 the National Monitoring Network recorded only two instances of the WHO guidelines on carbon monoxide levels being exceeded. The incidence of such high recordings will fall as more catalyst equipped vehicles enter service.
Handling tips
It was with some concern that I noticed the main photograph illustrating the article about a treatment for obese mice (This Week, 5 August). The correct way to handle rodents is not by the tip of the tail.
The Biological Council’s Guidelines on the Handling and Training of Laboratory Animals, published by the Universities Federation of Animal Welfare (UFAW), states: “Rats, mice and gerbils can be picked up by the base of the tail, while quickly supporting the body with the other hand; this prevents them from climbing up their own tail, and biting the handler. Rodents should never be picked up by the last third of the tail as they may shed it (as an anti-predator strategy).”
UFAW is a science-based animal welfare charity 鈥� we do not hold extreme views 鈥� and amongst other activities, we produce animal care material, such as The UFAW Handbook on the Care and Management of Laboratory Animals, to encourage animal users to treat them in the best possible manner.
Losing the thread
G. F. Dalton deploys K. G. Denbigh’s infinite regression argument against the idea that memory is laid down as physical traces in the brain (Letters, 19 August). He asks: how can you have a trace of a trace of a trace 鈥�?
This is not a logical difficulty, as he asserts, but one of mechanism. It arises from seeing a trace as restricted to a single level of reference, for example to objects in the world. However, there is no logical bar to a trace referring to anything, including another trace. In fact this must be the case for the trace theory to work, as memories are not restricted to a single level of reference either.
Consideration of simple data structures called linked lists may help here. Each item in a list consists of some data and one or more pointers which connect the item with one or more other items. The data are analogous to a memory of something, a pointer is analogous to the association of one memory with another. A program, analogous to (unconscious) mental processing, may retrieve a particular item by following the pointers, traversing the list structure until it locates the data/content it requires. The important point to note is that each item consists of two types of thing, not one.
Thus a trace must have this sort of complexity to be a viable candidate for human memory. In this sense, Dalton is correct: human memory does require a mechanism more subtle than simple traces.
Bite the other one
Your report on shark attacks at Recife, Brazil, swims by without taking so much as a nip at Fabio Hazin’s research (This Week, 19 August). As the article points out, a spate of shark attacks prompted the state government to ban surfing and bolstered Hazin’s shark research efforts 鈥� that is, killing 200 of them in order to study their behaviour and life cycle. His efforts reward us with the startling finding that local sharks had swallowed an onion, a pineapple and a can of beer. The hungry children of Brazil are also rewarded: Hazin gives them the shark meat to eat. Tsk, tsk. My heart bleeds like the shredded torso of a surfer bitten by a Tiger Shark.
No doubt Hazin’s research will end when there are no more sharks left to study, with the added bonus that the tourist area will once again be safe for surfers and swimmers.
New 杏吧原创 would do its readers and the conservation movement a service by investigating the type of “research” that Hazin is doing. In the meantime, as someone who comes from an area where shark attacks can occur, may I just say: if you don’t like sharks, then stay out of the water.
Current affairs (2)
Milsted may be looking for a sequel to his book. I suggest I Got it Wrong: The Guinness Dictionary of Regrettable Misquotations, starting with the one he ascribes to Richard van der Riet Woolley.
What the Astronomer Royal really said (I heard him on Radio Newsreel) was: “All this talk about space travel is utter bilge, really.”
Anyone who had seen the flamboyant articles about space travel and the imminent colonisation of the moon and planets that were splashed all over the newspapers in 1956, with science fiction-style illustrations, must have been immediately aware of what the new Astronomer Royal was riled about. The newspaper editors clearly did not like this so they deleted the first four words to make it appear that he was decrying space travel itself.
He went on to say:” It would cost as much as a major war just to put a man on the moon.” This turned out to be an accurate prediction.
One London paper printed his words truthfully but the lie had already gone around the world and nobody was interested in the truth still struggling to get its boots on.