Letter
So French researchers propose that gravity may be stronger at the poles where magnetism is stronger? Could there be a less esoteric answer? Surely a body near the equator is subject to the effects of centrifugal force as a result of the Earth’s spin which, to some extent, counters gravity and results in a lower weight reading.
The converse would be true at the poles. Given that the mass of the body has not changed, the difference in weight is likely to be interpreted as a change in gravitational effect. If this is true, then slimming clinics would do well to open at equatorial latitudes, where they could promise instant weight loss.
Michael Brooks writes: This is a confusion between G (Newton’s gravitational constant) and g (acceleration due to gravity). The latter is already known to depend on the location on Earth. The former is supposed to be a true universal constant.
Open and shut case
The opening sentence of your article on fire tests for doors appears to condemn steel fire doors (24 August, p 6). The sentence is inaccurate and is potentially damaging to the metal door industry.
The test door referred to in the article comprises steel sheets around a timber core and is therefore not a standard steel door, but an unfamiliar hybrid. Steel doors normally have two formed steel trays which totally enclose a core of honeycomb or insulation material 鈥� not timber.
The fire resistance test to which this hybrid product was subjected was based on a newly developed time-temperature curve intended to represent the specific 鈥� and restricted 鈥� case of hotel bedroom doors only. Even so, the curve displayed by Daniel Joyeux is not widely accepted, and British laboratories doubt that it is representative of real hotel fire conditions.
Your report says that only parts of doors are tested. This is not correct as hotel doors, like all others, are tested complete in their supporting frames with hardware fitted.
Peter Bressington says in the article that he supports timber doors, but has not appreciated that the door which failed the test was a timber door with metal sheeting.
The whole basis of this article appears to be flawed. Metal doors give much better protection than timber doors. They do not burn, but expand into their frames so acting as a fire barrier. Also, they do not cause flashback when subjected to a firefighter’s hose, as timber doors can.
Accidental dialling
Feedback’s article on cellphones dialling out to unwonted and unwanted numbers appeared in the same issue as one about Donald Norman’s belief that computer, robots, and therefore probably mobiles, should have emotions (5 October, p 46).
Consider this: my mobile is almost always off, and one day when I was sure it was off, I picked it up from the table next to me and found the screen light on. It displayed a valid British phone number which I didn’t recognise. When I checked my address list, it proved to be the Imax cinema in Bradford. So somehow, it had done three presses of one key and 15 of another, a long shot statistically, to get the only place of entertainment in its memory.
I prefer to believe that it was chiding me for failing to take it out more. Perhaps if the cinema can tell me what was showing at the end of September, we’ll know what it wanted to see.
Letter
The only time I’ve come across inadvertent phone use was a message left for me one morning on my answering machine by my then girlfriend. The message was a conversation between her and three friends in a cab on the way home from a girls’ night out, and must have been recorded when her cellphone accidentally dialled my number.
Needless to say, no one was spared. They gave their opinions of every bloke they had met that evening, who they’d tried to pick up, the failures and phone numbers taken.
My then girlfriend’s descriptions of her activities were very colourful. That was pretty much the end of my relationship with her.
Letter
The International Organization for Standardization’s test, which rates how long a fire door can endure as the temperature rises, is silly. There are two variables here: time and temperature. It would be better to rate the doors by the temperature at which they fail. Combining this with the experience of when that temperature is reached in a real fire would give a far more accurate estimate of the time people have to escape from a building.
Absorbing question
Isn’t global warming caused by an increase in total heat energy on the planet? How then can “forests help to cool the atmosphere as water evaporating from leaves absorbs heat”? (12 October, p 18).
Surely the heat energy is still there, in the water vapour, although the trees will be cooler. Total energy on the planet is still the same. If plants do not cool the planet by their transpiration, but just cool themselves, then the modellers will have to re-examine their assumptions and start again.
Danny Penman writes: It is true that the only direct cooling effect of increased transpiration will be on the trees and their immediate environment. But transpiration also leads to increased cloud cover, so more sunlight is reflected into space, thus cooling the planet.
Cut the claptrap
Your article on female circumcision states: “In cut women the breasts were the most sensitive area, suggesting that sexual sensitivity is conserved” (5 October, p 10).
That this is illogical nonsense is either obvious 鈥� as removal of the most sensitive organ will always result in another organ becoming the most sensitive, irrespective of any change in overall sensitivity 鈥� or becomes so on seeing it is logically equivalent to the statement: “In men whose hands are cut off, the feet are most used for writing, suggesting that writing skills are conserved.”
Letter
The idea of debiting the energy put into any energy scheme against that which it produces in its lifetime is clearly the proper way forward. But a paper I have written on this topic (“The total energy audit”) goes further, in that any proposed scheme or system for energy production should also undergo a “total carbon audit” to determine that it does not ultimately produce more carbon dioxide than it saves. In the nuclear case, for example, the CO2 emissions resulting from the manufacture of concrete, steel structures, vehicles, transport flasks and the long-term storage of spent fuel should not exceed those saved by actually going nuclear.
It’s a similar case with biomass fuels. These are normally regarded as carbon-neutral because CO2 produced in their combustion was taken from the atmosphere when the plants from which they came were photosynthesising. But if they require transport or fertilisers, and the manufacture or use of these items produces CO2 of fossil-fuel origin, they will cease to be carbon-neutral. We should therefore be thinking intensively about how to make “closed-cycle” biomass schemes where all processes get their energy from biomass.
Before there is huge investment of resources in any proposed scheme, both audits 鈥� energy and carbon 鈥� should be carried out. Accurate figures for these may not be available, but even a ballpark figure is better than none to start databases with, and precision can be improved and the relative viability of schemes revised as better databases are built up by experience.
Gravity of the situation
In recent issues there have been stories about the possible variation of gravity with magnetic fields. The article on “pinning down” gravity claimed that the variations in experimental results were due to the difference in magnetic field strength between Paris and Seattle (12 October, p 20).
Investigating the effect of a magnetic field on gravity must surely be a simple exercise, given that we can generate a field several orders of magnitude stronger than that of the Earth by the use of magnets. I also guess that any PC near the experiment would produce a stronger magnetic effect than that Seattle-Paris difference.
Another thought: any strong field, such as the Sun’s, should also have a major effect on gravity besides that due to mass. Has anyone looked for this?
Michael Brooks writes: The effect involves what is called the magnetic potential, not the field itself. The size of the effect depends on the distance from the magnetic field source. In the case of the geomagnetic field, that’s the enormous radius of the Earth, much bigger than the dimensions of any terrestrial laboratory.
There should be an effect from a directly applied magnetic field, but the apparatus would need to be more sensitive than anything currently available. The case of the Sun resembles that of the Earth, with the benefit of a much bigger radius. But the effect is predicted to decrease with temperature. Hence the effect is tiny in the Sun compared to the Earth.
All above board
I was profoundly disappointed to read so many errors in an article you published (21 September, p 5). My eye was drawn to the tendentious title: “UN is slipping modified food into aid”, which is tantamount to accusing the World Food Programme of wilfully sneaking genetically modified food into emergency aid, without the receiving countries’ knowledge.
On 23 August, the UN Secretary-General’s Special Envoy for Humanitarian Needs in southern Africa, James T. Morris, issued a statement on behalf of the Food and Agriculture Organization and World Health Organization, which stated: “There are no existing international agreements yet in force with regard to trade in food or food aid that deal specifically with food containing GMOs. It is UN policy that the decision with regard to the acceptance of GM commodities as part of food aid transactions rests with the recipient countries.”
As regards distinguishing between GM and conventional cereals, there is no international agreement obliging anybody 鈥� whether a commercial shipper or humanitarian agency 鈥� to test for GM. When asked by a recipient country about the content of food, the WFP does its best to supply information, but labelling is strictly a matter between donor and recipient.
There are no “large unsold stocks of GM maize and soya” in the US, as the article states. The US government buys commodities on the market which it then donates, and since market prices of all cereals are rising at the moment, there is no need to “drum up markets”.
As for trying to “break the European Union’s position on GM foods”, the European Commission clarified its position on GM organisms in a press release issued in Zambia on 23 August, in which it said: “The fact that a country grows GM maize has no impact on its ability to export other agricultural products to the EU.”
Opponents of biotech food are free to argue that people should starve while the scientific jury is out on GMOs. But do they have any viable alternatives? James Morris, who is also executive director of the World Food Programme, has already said that, without biotech food, it will be impossible to satisfy those in need.
Winning with wind
The answer to Roger Gibbons’s enquiry concerning the “energy gains” from alternative electricity generators (12 October, p 26) is nicely summed up on the British Wind Energy Association’s website ().
“The average wind farm in the UK will pay back the energy used in its manufacture within three to five months, and over its lifetime a wind turbine will produce over 30 times more energy than was used in its manufacture. This compares favourably with coal or nuclear power stations, which deliver only a third of the total energy used in construction and fuel supply. So if fuel is included in the calculation, fossil fuel or nuclear power stations never achieve an energy payback.”