Letters: That clock
The problem with Godalming station clock (Letters, 21 August) is, alas,
likely to be straightforward. Assuming we’re talking about a standard seven-segment
display, the problem will lie with the decoder ‘picking’ a bit. The timekeeper
will be (on the least significant digit, at least ) a binary coded decimal
(BCD) counter. Its four-bit output will be fed via a decoder to the display.
The decoder will effectively be a small read only memory (ROM), with 0-9
addresses, and seven-bit contents, each bit position equating to a specific
segment. Segments are commonly identified by a letter, the top horizontal
segment being ‘a’ and the others labelled around the perimeter clockwise.
The horizontal centre bar is ‘g’. The decode table of the ROM is given below.
Thus, if a ‘O’ is displayed as an ‘8’, the ROM has picked the ‘g’ bit
in location 0000.
Tony Howard, Norwich
Letters: That clock
The fault is not that the clock is selecting to display the wrong segment,
but that it is showing all segments. If this happens any number will appear
as eight, since it is the only number that uses all segments.
Matthew Willcox, London
Letters: Need to know
In asserting that ‘the ability to test (for Alzheimer’s) could be a
mixed blessing for those who dread the onset of the disease’ (New 杏吧原创,
Science, 21 August) Susan Katz Miller forgets the value of forward planning.
Caring for a sufferer can be an extremely expensive business – if full-time
committal to a home becomes necessary, 拢300 a week is not unusual.
Before the introduction in Britain this April of ‘Care in the Community’,
a social security allowance of up to 拢210 could be obtained against
this cost. Even with this aid, many husbands and wives of sufferers had
to sell their homes to make up the difference. This allowance has now been
abolished, and, where help has to be provided by social security, it has
power to sequestrate the whole of the sufferer’s assets – including pensions,
savings and share in the matrimonial home – to cover its costs.
At present action to save one’s dependents from penury and oneself from
an undignified end run up against the catch-22 situation that by the time
it becomes obvious that the disease is present the mind is too far gone
to take action. Until ‘living wills’ become legal, the value of a reliable
method of advance warning is obvious.
G. E. Haines Woodbridge, Suffolk
Letters: Missions to Mars
A number of reports appearing recently in international science and
technology journals have suggested that a Mars Observer failure would imply
a severe setback to the Russian-led international MARS 94 and 96 missions.
Your correspondent even stated that a Mars Observer failure would ‘wreck’
the MARS 94 mission (This Week, 28 August).
I wish to put the record straight by pointing out that in no sense would
the MARS 94 and 96 missions be compromised by a failure of Mars Observer.
The MARS 94 and 96 missions are not designed to be dependent on any other
mission to Mars.
It is true that Mars Observer, were it to be available at the time,
could act as a data relay facility for telemetry from the surface experiments
which both MARS 94 and 96 missions should deposit on the planet’s surface.
In the absence of Mars Observer, the transmission of data from the surface
stations would have to be carefully coordinated with the orbiters’ positions
in their elliptical orbits. Hence the availability of Mars Observer would
be advantageous in increasing the data transmission capacity from the
surface experiments. The extra data transmission capacity is, however, by
no means essential to fulfilling the MARS 94 and 96 mission requirements.
In any case, the experiments on board the orbiters, such as the German
stereo cameras, would derive no such benefit from Mars Observer and so would
be in no way affected by its loss.
Alan Harris Institute for Planetary Exploration Berlin-Adlershof, Germany
Letters: Boozy blast
An explosion has sent 7.4 million becquerels of radioactivity up the
stack in a Russian atomic plant (In Brief, 24 July). That is 202 microcuries,
or about the amount of radiation contained in 2170 hogsheads of beer. Considering
the problem that Russia has with alcoholism, perhaps radiation is the lesser
evil.
Robert Erck Argonne National Laboratory Illinois
Letters: Clouded vision
It is certainly true that the technique of culture of corneal limbic
cells (Technology, 28 August) could not be used for treatment of cataract,
but not for the stated reason. The real reason is that cataracts are to
do with the cornea.
Cataracts are caused by the progressive loss of clarity of the crystalline
lens within the eye, which sits behind the iris, several millimetres behind
the cornea. Following cataract surgery the cornea does occasionally become
cloudy due to damage to the endothelial cells on the intraocular surface
of the cornea caused by surgery. This could possibly be treated in the future
by ‘grafting’ of cultured endothelial cells. However, success in this area
is quite some way off because of the greater difficulty in both growth
of the correct cell, and methods of placing them on the inner surface of
the cornea in a way that does not allow them to escape onto other structures
such as the iris where they would cause major problems.
E. D. Allen Washington, Tyne & Wear
Letters: Leaning on the past
It is good to see some positive thinking by John Burland of Imperial
College, reported in ‘Pressure mounts to end Pisa’s decline’ (Technology,
21 August). The plan to stabilise the leaning tower of Pisa is, however,
a case of reinventing the wheel. It has all been done before – 183 years
ago in Clacton, when Captain George Whitmore righted Clacton’s Martello
C, a 15-metre tower weighing 3600 tonnes which had suddenly sunk 2 metres
on 18 October 1810.
Martello C was also built on clay and while it was only a quarter of
the weight and height of Pisa’s tower, righting it through 5 degrees was
no small problem. Captain Whitmore achieved it only four months.
He dug a series of holes and trenches 7 metres from the high side. These
he kept drained of water. He hung guns and iron shot on the same high side
and further weighted it with bricks. By manipulating his ground works, filling
some holes and extending others, the problem was solved in four months,
Martello C was straightened and the Napoleonic wars allowed to continue.
The cost was minimal, the thinking brilliant. Martello C still stands level
today, if a little lower than the rest of the towers, and without a crack.
I trust John Burland will have as much success at Pisa, even if he does
have to use more than bucket and spade. It seems today that no job can be
seen to be done properly unless you go ‘hi-tec’ and throw vast sums of
money at it.
C. J. N. Trollope Colchester, Essex
Letters: Cosmic importance
Members of the present government are often accused of possessing an
inflated opinion of their own importance. While browsing the current index,
issued with New 杏吧原创, I find that your publication serves only to
perpetuate this sorry state of affairs. The index lists two references to
‘The Universe’ and nine to William Waldegrave.
David Jones Sale, Cheshire
Letters: Amazing news
In This Week (7 August) you carry two items on cats: in one, the shocking
conclusion that tail position reflects mood, and that cats share favourite
spots; in another, that handling kittens boosts their friendliness, and
that Siamese and Persians are among the friendliest breeds. Wow! Move aside
oncogenes, let’s really talk revolutionary results!
John Humphreys Birmingham
Letters: Sound for sight
I am a regular New 杏吧原创 reader. Unlike the vast majority of readers
however, I read the magazine by listening to an audio tape. This is because
I am blind. The Talking Newspaper Association of the United Kingdom (TNAUK)
record the magazine weekly (as much as will fit) onto a C-90 cassette. This
is an excellent service for which I am eternally grateful. When I returned
from holidays recently I found a collection of cassettes waiting for my
attention on the doormat. I was particularly interested in ‘Computer games
paint sound pictures for the blind’ (This Week, 7 August).
The article overlooked some points. For the past six months I have been
using a product called ‘Slimware Window Bridge’ (SWB) from Syntha-Voice
Computers Inc, Hamilton, Ontario, Canada. This product, together with the
Dolphin Apollo 1 speech synthesiser, allows me to work with Microsoft Windows
although I can’t see the screen. I use applications such as word processing,
spreadsheets and terminal emulation, as part of my work in the computing
department of AIB Bank.
I have typed this letter (and checked the spelling!) using the Word
for Windows word processing package. The access software echoes the keystrokes
on a set of headphones as I type and I can ask the software to read back
a character, a word, a line or the entire screen. When the mouse pointer
lands on an icon, the speech software speaks the name of the icon, such
as ‘edit’. If a new icon is encountered which the software does not recognise,
I can ask a colleague to tell me what the icon represents. I can then key
in a suitable verbal description which the access software will store. The
next time the icon is encountered, my label will be spoken by the speech
synthesiser.
If I want to locate my position on the screen or in the document this
can be done quite easily. For example if I place the cursor at the letter
I at the start of this paragraph and ask the cursor position by pressing
a key sequence, the synthesiser says ‘Page 1 line 38 column 1’. If I ask
the pixel position it says ’39, 124′. This tells me the absolute screen
position. The top left corner of the screen is 0,0 and the bottom right
is 640, 480. By asking the software to read certain parts of the screen,
I can see what fonts and point sizes are being used.
The National Council for the Blind of Ireland is currently considering
setting up a training course in Windows word processing for blind people
using this software. I think this is a realistic aim although there may
be some teething difficulties.
Finally, I would like to take up the point in your article attributed
to Paula Fabrici, that ‘Windows would be obsolete before blind people get
access’. Very fortunately for me, as I hope this letter shows, this is not
the case.
Ronan McGuirk Glenageary, Co. Dublin Ireland