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‘Nor does the initial experience with the telescope
provide such reasons. The first telescopic observations of the sky are
indistinct, indeterminate, contradictory and in conflict with what everyone can
see with his unaided eyes. And the only theory that would have helped to
separate telescopic illusions from veridical phenomena was refuted by simple
tests’
Feyerabend argues –
the problem of telescopic vision is different for celestial
and terrestrial vision –
it was thought to be different at Galileo’s time because of
the idea that celestial and terrestrial objects are formed from different
materials and obey different laws
this means that the result of an interaction of light with
terrestrial objects cannot be extended to the sky
added to this is the idea that the senses are acquainted
with the close appearance of terrestrial objects and are able to perceive them
distinctly – even if the telescopic image is distorted
the stars are not known by close acquaintance
therefore we cannot use our memory for distinguishing the
effect of the telescope from the object itself
also all the familiar clues which aid terrestrial vision are
absent when dealing with the sky – and new phenomena abound
only a new theory of vision containing both hypotheses could
bridge the gap between terrestrial (unaided vision) and celestial (telescopic)
experience
Feyerabend’s first task is to –
‘comment on the contradictions and difficulties which arise
when one tries to take the celestial results of the telescope at their face
value, as indicating, stable, objective properties of things seen.’
he refers to the fact that many of Galileo’s contemporaries
regarded what was seen in the telescope as unsatisfactory or illusory
he mentions here Aristotle’s explanation that the senses
applied in abnormal conditions are likely to give abnormal results –
he also points out that in the 16th century they were
unaware of strong positive illusions
the extent of which was not realized until the work of
Ronchi – who showed that the greatest variations have to do with the placement
of the telescopic image – and correspondingly – in the observed magnification
some observers placed the image inside the telescope –
making it change its position with the lateral position of the eye – as it
would be with an after image – or a reflex inside the telescope
this was regarded as an excellent proof of illusion
others placed the image in a way that led to no
magnification – when a magnification of over thirty had been promised
even a doubling of images can be explained by a lack of
proper focusing
in my view here we are primarily talking about instrumental
limitations – and problems that come from the lack of a secure theory and
protocol of usage
Galileo reports unevennesses at the inner boundary of the
lighted part of the moon while the outer boundary appears round and circular
the moon appeared to be full of mountains at the inside but
smooth at the periphery –
despite the fact that the periphery changed as a result of
the moon’s librations
the moon and some planets such as Jupiter were enlarged
while the apparent diameter of the fixed stars decreased – the planets were
brought nearer while the stars were pushed away
Galileo says –
‘The stars, fixed as well as erratic, when seen with the
telescope, by no means appear to be increased in magnitude in the same
proportion as other objects, and the moon itself, gain increase of size; but in
the case of the stars such increase appears much less, so that
you consider that a telescope (which for the sake of
illustration) is powerful enough to magnify other objects a hundred times, will
scarcely render the stars magnified four or five times’
Feyerabend
says the strangest features of the early history of the telescope can be seen
when we have a look at Galileo’s pictures of the moon
‘It needs only a brief look at Galileo’s drawings, and at
photographs of similar phases, to convince the reader that ‘none of the
features recorded….can be safely identified
with any known markings of the lunar landscape.’ [Kopal]
Looking at such evidence it is easy to think that ‘Galileo was not a great
astronomical observer; or else the excitement of so many telescopic discoveries
made by him at the time had temporarily blurred his skill or critical sense’
[R. Wolf]
Feyerabend has his doubts about this view in light of the
‘quite extraordinary skill which Galileo exhibits on other occasions’ – here
referring to Galileo’s discovery and identification of the moon’s of Jupiter
he argues there are other hypotheses which lead to new
suggestions which show just how complex the situation was at the time of
Galileo
Feyerabend goes on to consider two such hypotheses –
hypothesis I
‘Galileo recorded faithfully what we he saw and in this way
left us evidence of the shortcomings of the first telescopes as well as the
peculiarities of contemporary telescopic vision’
Feyerabend thinks that what would be needed to establish
this view would be an empirical collection of all the early telescopic results
– including all the pictorial representations that have survived
but this he notes is a yet to be written history
hypothesis II
‘hypothesis II, just like Hypothesis I, approaches
telescopic reports from the point of view of the theory of perception; but it
adds that the practise of telescopic observation and acquaintance with the new
telescopic reports changed not only what was seen through the telescope, but
also what was seen with the naked eye.’
Feyerabend’s view is that this hypothesis has many
difficulties – and perhaps should be given up
however he thinks that looking at this hypothesis is
important for our evaluation of the contemporary attitude to Galileo’s reports
first up Feyerabend summarizes the situation Galileo was in
–
Galileo was only barely acquainted with contemporary optical
theory
his telescope gave good results on the earth
in the celestial realm the telescope produced spurious and
contradictory results that seemed to be refuted by the unaided eye
a new theory of telescopic vision was required to separate
appearance and reality
such a theory was developed by Kepler in 1604 and 1611
‘According to Kepler, the place of the image of a punctiform
object is found by first tracing the path of the rays emerging from the object
according to the laws of (reflection and) refraction until they reach the eye,
and then by using the principle (still taught today) that ‘the image will be
seen in the point determined by the background intersection of the rays of
vision of both eyes’ [Werke] or in the
case of monocular vision, from the two sides of the pupil. This rule which
proceeds from the assumption that ‘the image is the work of the act of vision’,
is partly empirical and partly geometrical. It bases the position of the image
on a ‘metrical triangle’ or a ‘telemetric triangle’ as Ronchi calls it, that is
constructed out of the rays which finally arrive at the eye and is used by the
eye and the mind to place the image at the proper distance. Whatever the
optical system, whatever the total path of the rays from the object to the
observer, the mind of the observer utilizes its very last part only and
bases its visual judgement, the perception, on it.’
Feyerabend says this is an advance on previous thought – but
entirely false
take a magnifying glass – determine its focus – and look at
an object close to it
the telemetric triangle now reaches beyond the object to
infinity
no such phenomenon is ever observed
we see the image slightly enlarged in a distance that is
most of the time identical with the actual distance between the object and the
lens
the visual distance of the image remains constant – however
much we may vary the distance between lens and object – and even when the image
is distorted
I am rather surprised at this argument from Feyerabend
Kepler’s telemetric triangle is a calculation – it is not a
phenomenon
so arguing that it is not observed – is no argument against
it
what you have from Kepler is a theoretical model for vision
– a decision – in short on how to define vision
and this model – as with any such model – is open to
question – open to doubt –
is uncertain
Feyerabend concludes with –
‘This then was the actual situation in 1610 when Galileo
published his telescopic findings. How did Galileo react to it? The answer has
already been given: he raised the telescope to the state of superior and better
sense’
I take the view that Galileo’s success here was an intuitive
success
his argument was an argument for common sense – and an
argument for the common man
common sense tells us and the denizens of the 16th century
that vision is variable –
that it is relative –
you do not need to enlist a telescope to realize this – just
step back from or move closer to what you are observing – to see the difference
– to be aware of the relativity
the argument of the telescope is really just the common
sense relative vision argument –
in the instrument of a telescope
I am of course here quarantining the 16th century mind and
for that matter the modern mind to the context of vision – minus the extraneous
considerations of cosmological theory
Galileo’s problem was never the question of what can be seen
or understood by those with their eyes and minds open –
his problem was that of dealing with those in the political
philosophical and religious domains who had (and still have) a invested
interest in propagating theoretical and empirical blindness
Galileo was deeply involved in theoretical uncertainty and
he was deeply involved in observational uncertainty
what we have in the work of Galileo is an exploration of
those propositional uncertainties
and it is this exploration of uncertainty that leads to the
growth of knowledge –
uncertain knowledge
