Letters: Twins win
I was delighted to read Mick Hamer’s piece (Technology, 24 April) describing
a proposed new oil tanker design with a twin diesel-electric propulsion
system which might have avoided the recent Shetland (Braer) oil disaster,
when water pollution stalled the ship’s single engine.
I have been actively criticising the technical design of oil tankers and
particularly liquid natural gas carriers since 1973, when I first saw a
design model of a large single-engine, single-rudder carrier intended to
carry bulk liquid natural gas from Sarawak to Japan. Since then I have
actively pressed in newspapers and journals for professional designs
incorporating twin engines, twin propellers, twin rudders, twin steering
engines plus fore and aft thrusters.
I note that even this new breakthrough oil tanker design has only a single
propeller with coupled engines, which means the crew could not steer it by
engines alone. This was a factor in the Amoco Cadiz, which fouled the coast
of northern France when its single-steering engine failed.
Why spoil this new, highly innovative design by not having full twin
redundancy, with twin propellers, twin rudders and twin steering engines?
W. G. Burns
Canberra, Australia.
Letters: Catching crocs
Your correspondent reported that, Oliver Schiebe, a game ranger in the
Australian Northern Territory, was pulled into the river by a crocodile he
was capturing, suffering a broken hip and a gouged abdomen in the process
(This Week, 15 May). The technique reported to be used on the crocodile
sounds a bit rough, even for the home of Crocodile Dundee. The crocodile is
harpooned in the neck, then hauled into a boat. Prior to release the head of
the harpoon is removed and antibiotics applied.
Is there poor scholarship here? Are the Australian rangers unaware of the
international literature concerning nontraumatic crocodile capture? We would
cite methods described by Earl in 1954 (capture pen), Chabreck in 1965 (pole
and noose) or Murphy and Fendley in 1974 (trap).
One of the recent additions deserves particular attention. The Kofron method
(1989) consists of an ingenious trap and noose fashioned so that when a
‘croc’ takes a bait (meat or dead dog) a steel loop tightens round its lower
jaw. A team then hauls the reptile ashore securing jaws and legs with rope
while a sack is placed over the head.
After completion of scientific investigations the reptile is released. This
is the tricky bit. The legs and tail are untied and held by team members.
The team leader moves well away with a rope attached to the sack and jaw
binding. Those holding the legs leave one team member (perhaps known as the
‘mug’?) holding the head. At a shout from the leader, the mug drops the head
and runs (like hell). The leader uses the rope to pull off the sack and jaw
binding.
Kofron records that only 10 per cent of specimens feel aggrieved enough to
chase the team and the method is so nontraumatic that some return to sexual
recreation shortly after release (the crocodiles that is). The contrast with
the harpoon technique is profound. Some might say that the response by
ranger Scheibe’s crocodile was fully justified.
Angus Nicoll and
Mary Braham
St Albans, Hertfordshire
Letters: Eye shadows
I am sorry to deprive G. S. Holister of his place in the history of visual
science (Letters, 29 May) but the effect which he describes is a well-known
one.
As an optician, I am frequently asked by patients, particularly children,
about the tree-like pattern which they observe while I am using my
ophthalmoscope. It was indeed his retinal blood vessels (or rather their
shadows) which Holister was observing, but the effect derives from the
remarkable structure of the human eye.
The blood vessels of the retina actually lie in front of the photoreceptors
(an arrangement which surely confirms a Darwinian rather than divine origin
of the eye). What is remarkable then is not that the retinal vessels are
visible under certain lighting conditions, but that we are all not
continuously aware of their presence.
It is the ability of the eye-brain system to filter out such fixed images
that prevents our visual world being confused by superfluous information.
When light is shone obliquely into the eye, different photoreceptors from
those normally used are involved and the retinal vessel ‘tree’ becomes
visible, particularly in the dim lighting of an optician’s consulting room.
Douglas Dickie
Aberdeen
Letters: Eye shadows
The phenomenon in question is well known to opticians, and was first
described in 1819 by Jan Purkinje, a Czech physiologist.
Adrian Stanley and Zoe Whorton
Solihull, West Midlands
Letters: Eye shadows
The ‘Holister Effect’ sounds like the effect produced by one of the exhibits
in ‘Science Alive.’ the hands-on science centre here at Snibston Discovery
Park. In our ‘Blood Vessels’ exhibit, the user rests a small light on their
closed eyelid and wobbles it to-and-fro, producing just the effect
described – sharp black blood vessels against a pink background, these
being the blood vessels running across the retinal surface.
Ian Simmons
Leicestershire County Council
Snibston, Leicestershire
Letters: Eye shadows
All one needs to do to observe the retinal blood vessels is to look through
a pinhole in a piece of card: the slightest movement of the card will
immediately bring the vessels into sharp focus.
Donald Brett
Rickmansworth, Hertfordshire
Letters: No cousin of mine
Richard Dawkins (‘Meet my cousin, the chimpanzee’, 5 June) surely
exaggerates when he claims that the discovery of a surviving intermediate
between mankind and the chimpanzees would cause our previous system of norms
and ethics to come crashing down.
The idea that we are close relatives to the apes has been around for some
time now. Dawkins is right to point out that we should be treating them with
a proper respect, but is he not guilty of speciesism by stopping his chain
of parent-child bonds at the man-chimp common ancestor? Why not go back all
the way to the first replicating organism or beyond and ‘meet my cousin, the
rock’?
Dawkins is famous for the strategy of ontological reductionism, that of
saying that we are ‘nothing-but’, which reduces man to just apes, apes to
just ‘selfish genes’, and genes to just molecules. But life has emerged from
inanimate matter, intelligence has emerged from living organisms and
conscious self-awareness, with norms and ethics, has emerged in Homo sapiens
from intelligent apes.
By failing to see the validity of these emergent properties, which have an
authentic existence of their own, he is blind to their nature and the rules
which they follow.
G. A. Barber
Twickenham, Middlesex
Letters: No cousin of mine
Whatever the biology of it, humans are distinctly different from chimpanzees
– in many ways that herring gulls are not distinct from black-backed gulls.
The two species of bird occupy basically the same niche around the globe and
behave as a single ecological species, if not a taxonomic one. Man and the
apes clearly do not have a similar ecological impact and other differences
between ‘us’ and ‘them’ are profound: we write, we philosophise, we cook,
we make music, and so on.
Matthew Hosier
Hove, East Sussex
Letters: Lorry subsidy
The transport minister proposes to set the new motorway tolls on the largest
juggernauts at 4.5p per mile, just three times that levied on cars. Yet that
level is nowhere near the relative road cost of lorries. Evidently John
MacGregor wants car users to subsidise lorries even more than at present and
wants to shield juggernauts from meeting their real road costs.
Damage and wear to roadways depends very strongly on axle weight –
officially, it increases to the power of four in relation to the weight –
and the costs of 38-tonners in terms of damage are hundreds of thousands of
times that of a typical car. In addition, the costs of building new roads
and bridges are strongly dependent on the design loading. Two thirds of the
cost of the new Severn Bridge could be saved if it was designed for maximum
24-tonne rather than 40-tonne juggernauts.
If the heavier lorries had to meet their real road costs on new private
motorways, they would doubtless choose, in most cases, to divert via the
existing roads. So such motorways would be built cheaply for light cars and
vans alone. Such an option would have made sense for the duplicate Severn
Bridge. But the Department of Transport has always tried to conceal lorries
as ‘traffic’ and to keep all roads open to the heaviest juggernauts.
When the former chancellor, Norman Lamont, talked to the CBI (26 May) about
‘bringing market disciplines to bear more directly on road users’, was he
prompting John MacGregor to stop the massive subsidisation of juggernauts?
Max Wallis
University of Wales
Cardiff
Letters: Influence of TV
I was interested to read ‘When the medium’s message is violent . . .’ by
Jerome Burne (29 May). The question posed was whether television violence is
a benign reflection of society’s mood, or an agent provocateur?
Advertising cigarettes on television is now banned because, we are told, it
might influence children to smoke. Also, commercial companies, political
parties, and government agencies all – at vast expense – use television as a
means of influencing public opinion.
If we believe those who tell us that violence on television has no influence
on the level of violence in society, we must also believe that the agencies
which spend billions of pounds on television advertising are wasting their
money.
Derek Coggrave
London
Letters: Teething problems
As a dentist in general practice, I found the article ‘The white heat of
laser dentistry’ (22 May) quite interesting. Unfortunately, it failed to
address some quite important questions.
In general practice most of our work is concerned with replacing existing
metal and composite fillings and not so much with the preparation of virgin
teeth. Also a varying number of teeth are prepared for crowns. Therefore, I
have a number of queries. Can lasers be used for the removal of amalgam from
teeth, bearing in mind this is a mixture of mercury, copper, tin and zinc
and would this lead to the formation of toxic, possibly highly reactive
substances being produced?
Also, bearing in mind the metallic nature of dental amalgam, how would this
affect the heat produced by the laser and its transmission to the vital
dental pulp?
Finally, how would one prepare a tooth for a crown? This normally involved
the removal of between 1 and 3 millimetres of tooth substance from all
surfaces of the tooth making all sides of the tooth taper roughly five
degrees, while ensuring no undercuts are present relevant to each surface.
I also notice from the picture accompanying the article, that the patient is
not wearing protective eye-wear. Is this situation correct?
Howard Koch
Hemel Hempstead
Hertfordshire
Letters: Teething problems
YAG does not stand for ‘yttrium arsenium gallium’ (arsenium indeed.) but
‘yttrium aluminium garnet’. It is, in other words, a material with the same
crystal structure as common garnet but with yttrium in place of the more
usual iron or magnesium. The neodymium, which is the element that emits the
laser light, is present in this matrix as an introduced impurity or
‘dopant’.
Ian Stewart
University of New England
Armidale, NSW, Australia