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No demon
The Hilsh tube, also known as a vortex tube, described by F. G. Grisley (Letters, 26 November) is, unfortunately, not an example of Maxwell’s demon at work.
The vortex tube was invented by Ranque in 1933 but it would seem that Hilsh (1947) was the first to study the device in detail. What occurs within the volute is essentially an interchange between kinetic energy and thermal energy although the exact nature of the mechanism is not fully understood. In order to conserve angular momentum the air spiralling toward the centre of the volute chamber, where it can exit through the hole in the diaphragm, will try to accelerate.
This acceleration is opposed by the action of viscosity, which results in an exchange of kinetic energy between the air at different radii in the chamber. Whatever the precise mechanism, there is no doubt that cold air issues from one end of the device (the diaphragm end) and hot air from the other (the throttled end). In our own experiments temperatures of 鈭�30 掳C and below were measured at the cold end with corresponding warm end temperatures up to 80 掳C for an air inlet temperature of 20 掳C and pressure of 0.6 megapascals.
Since only about 30 per cent of the feed air leaves through the cold end it is clear that the increase in entropy of the hot stream is considerably greater than the decrease of the cold stream and hence the net change in entropy is positive. Further, whilst the temperature difference generated could, in theory, be used to drive a heat engine the work output would be considerably less than that had the feed air been expanded directly through a turbine. The vortex tube is certainly an intriguing device but it does not contravene the Second Law and we shall have to look elsewhere for our demons.
British first
In Brief (26 November) refers to the inauguration of the world’s first fully remote controlled ground-based telescope.
The world’s first robotic telescope includes fully remote control features. The telescope has been developed at Bradford University and is currently operational. It is located in the Pennines and is accessible via the base station at the Department of Industrial Technology at Bradford University. You can reach it on the Internet at
The telescope is popular with astronomers and others linked to the Internet. Over the last week there have been over 100 000 requests serviced by the telescope base station.
Screwed up
At last scientific proof of what I and many other DIY furniture assemblers have known for a long time: that the cross-cut screw is vastly inferior to any other type (Technology, 3 December) and has an amazing consistency in that the cut gives way when the screw is approximately two thirds of the way into the wood. Can we now look forward to consumer groups campaigning to abolish this major source of stress in the modern household?
Zapped by Year 9
I was interested to read Barry Fox’s article on “smart zappers” (Review, 19 November). I could have used the information two months ago, however.
As a teacher in a local secondary school, I am timetabled for two Year 9 groups on a Thursday afternoon and decided one week that a video was particularly relevant. Lesson 1 went well; no technological hitches and an interested class. Lesson 2 was not so successful. After only a few minutes the volume increased, then returned to its previous level. This was repeated a number of times; the VCR went into picture search and back to normal play; it stopped completely and restarted 鈥� all of its own accord.
I had the remote control. There was obviously another 鈥� which I couldn’t see 鈥� or a jinx in the machine. After 20 minutes I aborted the exercise.
It wasn’t until the next day I overheard the comment that a particular rogue in Year 9 had a watch which doubled as a remote control.
I was most relieved to realise the experts at the electronics exhibition could be fooled as I was. I don’t feel quite so bad after all.
Tellystereograms
I was intrigued from the outset with autostereograms (AS), that is, once I had mastered the awkward art of actually seeing an AS (see “How to play tricks with dots”, 9 October 1993).
I notice that you can see round them to a degree and from varying angles as with real 3D. So I would like to suggest an experiment for those with suitable equipment to carry it out.
If they were to create a few seconds worth of “cartoon” AS footage of progressive motion from an original starting point and back to it 鈥� for example, two balls in mutual orbit around each other 鈥� this could be played back on a monitor (which I know will reproduce an AS because I’ve tested it with my video camera) for sufficient time to adjust our eyes to see the effect.
The point of the test, of course, is to see if motive AS footage can be reproduced for future 3D television. The point of success would be that we could look towards 3D viewing with present-day technology, a vastly superior alternative to creating perhaps unnecessary new technology to do the same job, and instantly accessible to all.
Assuming that, given success, computers can intermingle two-shot images from real life in the manner of AS presence, we’d see a jumble of moving lines and no images until we settled our eyes (brains) to viewing properly, but practice would probably make viewing such TV almost as easy as viewing is today, and it’s a lot more comfortable than wearing a pair of coloured specs.
Anthropic physics
What Steven Weinberg disparagingly describes as “metaphysics” (Forum, 26 November) turns out, on close examination, to be nothing more than the attempts made by interested and intelligent people to understand the significance of an important branch of science.
The alternative to doing this is that we are left with a physics which is devoid of any meaning for lay people 鈥� since explanation inevitably involves interpretation, which involves “metaphysics” or “philosophy”. The result of Weinberg’s “physics not metaphysics” would ultimately be a caste system of scientists and lay people, with no possibility of communication between them.
The so-called “anthropic principle” was not formulated by desperate and craven “philosophers and theologians” in the face of honest-to-goodness “scientists” eager to get on with their jobs. On the contrary, scientists have been as responsible as anyone else for its formulation. The best known exponent of the anthropic principle in Britain is undoubtedly Paul Davies 鈥� a physicist at the very forefront of his discipline.
Anthropomurphism
The concept of quantum Murphic tunnelling was critically reviewed by Graham Hagen and others (Letters, 27 August, 17 September and 15 October). While this is undoubtedly an important aspect of Murphism which permits things occasionally to get done (presumably) right, it tends to obscure a much deeper question with which Murphicists must now come to grips. It is necessary to examine the precise nature of the major concept of Murphy’s law, namely “wrong” (as in “If anything can go wrong, it will”).
The concept of wrongness in a situation, consequence or action requires conceptual cognition, which is an anthropomorphic attribute. (This does not, of course, refer to simple physical incompatibility, as a square peg is wrong for a round hole, or 2 + 2 = 5). Thus the anthropomurphic cosmological principle states that the law can only operate when it is being tested by a human (that is, whenever anyone tries to do anything), because at other times no definition of “wrong” is possible. Thus many things may actually be done right because they happened when no one was looking.
The advantage of this principle over Murphic tunnelling is that it is quantifiable, and furthermore it relieves everybody of the need ever to try consciously to do anything.
Despite the enduring interest of this topic, this correspondence is now closed 鈥� Ed
Divers' daughters
The comments on divers and the sex of their offspring (“Why presidents have more sons”, 3 December) reminded me of a meeting of the British Tunnelling Society a number of years ago when the members were asked how many had worked in compressed air and only had daughters. The response from the floor showed that a large majority were in this peculiar situation.
It would be interesting to see if there was the same response today as recent advances in the methods available for excavating tunnels through difficult ground conditions mean that less men now have experience of working under compressed air conditions. If there is a connection between working under compressed air and the sex of children the ratio of daughters to sons should now be closer to one.
For the record, in this office the engineer who has spent most of his career in mines and rock tunnels has three sons. Of the three engineers with extensive experience in compressed air one has three daughters and another has two daughters and one son. The third has two sons, both of whom were born before he worked in compressed air.
Big bang bunk
Your article “Rebel with a cause” on Grote Reber (29 October) in Tasmania, now 83 and setting up a radio astronomy centre to disprove the theory of the big bang, made me (a holder of a similar view) write to him. His succinct reply is worth publishing.
He writes: “I contend the red-shifts have nothing to do with motion. It is not my idea. Hubble knew this over sixty years ago. See his book Observational Approach to Cosmology, Oxford Press, 1937. He discusses this on page 63. Also see his last sentence on page 66. See my article in Journal of the Franklin Institute, January 1968, p 1-12. The big bang is a concoction of latter day saints.
“I’ve lectured numerous times under the title The Big Bang is Bunk. Always a large audience. A lot of people are fed up with big-bang creationism and all that goes with it.”
Grote Reber continues in light vein: “The drawn picture of me [in New 杏吧原创] makes me look very old. My eyes don’t squint, nor is my face deeply wrinkled. I’m very annoyed. They should do better.