Editor's pick: 3D printing: you read it here first
Chuck Hull undoubtedly made stereolithography or 3D printing a practical reality (22 October, p 40). But he was not the first to suggest it. 快猫短视频 played a small part.
Older readers recall fondly the wonderful inventions of Daedalus, a weekly contribution to your back page by , a chemist from Newcastle upon Tyne. Daedalus was the archetypal mad scientist, totally amoral and lacking in all common sense. Most of his ideas have, thank goodness, never seen the light of day, but occasionally he came up with a properly feasible scheme by accident. Thus he found himself proposing more or less exactly the same kind of stereolithography that Chuck Hall developed 10 years later ().
Editor's pick: 3D printing: you read it here first
Daedalus imagined a process very similar to, but earlier than, Chuck Hull's first method of 3D printing in 1983. He that would be polymerised when simultaneously illuminated at two frequencies. Directing two laser beams into a vat of the stuff would create a solid object of absolutely any shape – “even complex interlocking and re-entrant shapes quite impossible to mould”.
London, UK
Several reasons to feel very tired
Emma Young treats fatigue as if it were only a medical problem (15 October, p 28). In many cases it can be an engineering issue. As a designer of heating, ventilation and air-conditioning systems with over 30 years' experience, I believe that I have stumbled over some of the traps.
Willis Carrier was the first person to design a modern air-conditioning system. His designs called for about 20 per cent of the air passing through the system to come from outside the building. This ventilation component uses about 50 per cent of the system's energy, on average, so there is a temptation to reduce the outside ventilation. Chemicals from carpet, furniture, building materials and even people can then pollute the air and make us feel tired.
In Carrier's designs conditioned air came into contact only with zinc on galvanised steel or with the copper of cooling coils. Zinc and copper have recognised antimicrobial properties. But in the 1970s came new designs using materials such as aluminium, with few or no such properties.
Several reasons to feel very tired
I was surprised that your very interesting in-depth article on tiredness made no mention of caffeine. Like virtually everyone I know, I regularly consume tea, coffee or cola to boost alertness on a temporary basis. I wonder whether the tiredness many complain of is not in fact simply a withdrawal symptom?
Several reasons to feel very tired
I suggest one more factor that could result in tiredness – noise. My kitchen has a washing machine, tumble drier, fan oven, electric kettle and microwave, and even the new taps are noisier than the old ones. One or other of the family usually has radio, TV or CD player on. Outside, traffic is heavy and noisy; shops and restaurants often have music playing…
Several reasons to feel very tired
Thank you for providing sensible explanations for the feeling of being tired all the time. There is a further simple possibility: carbon monoxide (CO) poisoning stemming from faulty heating or cooking appliances powered by any carbon-based fuel, including gas, coal, oil, petrol or wood.
At very low concentrations, include headache, tiredness and confusion. It cannot be detected directly by any human sense. A concentration of less than 2 per cent CO in the air can kill in between 1 and 3 minutes. The independent charity has lobbied government and industry since 1995 for prime-time TV warnings about this.
We have been ignored – or told that such warnings are “so last century”.
First class post
People are more tendentious than I can ever recall. It's terrifying that reasoning has no effect.
Renee Lascala by the challenge the US faces in healing its political rift after the election (5 November, p 18).
No reason to kill 'problem' wildlife
Animal rights researcher BiddaJones identifies three circumstances that supposedly “justify lethal wildlife control” (22 October, p 18). Of course, none really do.
As Alice Klein reports, killing “problem” animals hasn't really worked in the long run when mass slaughter is the method of choice. What I found surprising is that there is no mention of the rapidly growing international field called “compassionate conservation”, something Dan Ramp and I wrote about for 快猫短视频 (21 June 2014, p 26). A number of the examples of culling wildlife given are from Australia, where killing often is “the name of the game”.
It would be good for those who vote to kill so-called problem animals to first visit the Centre for Compassionate Conservation at the University of Technology, Sydney. Numerous humane non-killing alternatives exist and need to be implemented – because killing doesn't work and raises numerous ethical questions for which there are no easy answers.
Many reasons for longevity boost
There are more reasons than Clare Wilson gives for life expectancy in the UK increasing throughout the last century(8 October, p 10). Infection control should not be overlooked. There were 250 deaths from tuberculosis alone per 100,000 people at its peak, now reduced to almost zero.
Lung and stomach cancer decreases in men account for a further 65 per 100,000 – in large part due to changes in tobacco use and environmental controls. The decrease in the cardiovascular death rate for the same period is 150 per 100,000 – also due in part to environmental changes, as well as lifestyle changes and to improvements in emergency care and dental health.
The two most authoritative medical journals in the UK are at odds over how much statin drugs have contributed.
Peace in the valley with plenty for all
David Flint questions whether peace and equality could have existed in the Indus Valley for 700 years without birth control, or conflict (Letters, 15 October). But today we find that the birth rate goes down, not up, in developed, war-free cultures.
If the Indus culture was not consumerist, there would have been adequate resources for all. That aside, the idea that we need conflict before we can enjoy peace is one of the greatest oxymorons afflicting our culture today.
Having a whale of a time saving seals
Robert Pitman suggests that humpback whales are helping seals escape killer whales because of inadvertent altruism (15 October, p 42).
I can see another possible explanation, beside weakening the killer whales or reducing their numbers, so that more humpback calves survive (Letters, 5 November). Could the seals be helpful to the humpbacks in a way that we are not yet aware of, so that the humpbacks are protecting them for that reason?
Having a whale of a time saving seals
I can see another benefit for whales protecting seals from orcas. It is play. Young mammals learn by playing; for some species playfulness continues throughout adulthood, making these creatures better able to learn and adapt than those tied into instincts locked in their genes.
“Balance your enemies' food out of reach” sounds like fun. If I were a humpback whale, I'd want to play that game.
Beaver-scented perfumes take guts
You note that beavers' anal secretions are used in perfume and other products (22 October, p 36). I'd like to know about the brave men and women who do the harvesting. It's not easy even to capture a beaver. I once lived on a property with an artificial lake. There was an overflow cut into the dam, which was key to preventing it washing away – but the beavers didn't like that strategy, and kept damming it up.
Many nights I'd have to go out during lightning storms and confront them, tearing down as they built. I was braver then.
Harvesting these secretions sounds doubly difficult.
How are the odds on climate change?
While reading of Jules May and Andrew Collins's bet on whether global mean temperature would exceed that of 2015 within 10 years (Letters, 22 October) I saw the Italian RAI 24 news station that 2016 was well on course to break the 2015 record.
The most exciting aspect of the bet may be how many post-Brexit pounds May will need to pay the $1000, early next year.
Partying, or not, time after time
Jonathon Keats reports Stephen Hawking issuing invitations to a party for time travellers after the event (10 September, p 42). If I hold my own party, can I validly be at all disappointed at non-attendance until I actually issue the invitations?
At that stage I can presumably become disappointed, both in the then present and retrospectively.
What, though, if someone did turn up at the party? I would feel very tempted not to issue the invitation, just for the hell of it. Perhaps, though, nothing would happen (or would have happened, or be about to happen) until the actual moment I didn't do it.
Who is stealing whose genes?
How can Sarah and Seth Bordenstein be sure that the WO bacteriophage stole its genes from a spider (15 October, p 8)? Could the black widow spider not have acquired its poison gene from an invading bacteriophage?
Stirling, Western Australia
The editor writes:
• The gene is more likely to have originated with the spider. It is much longer and more complex than most viral or bacterial genes, and it has sequences with which other spider genes can interact.