Direct measurement of temperature

In an earlier post, I described the representation measurement of temperature.  In this post, I describe the direct method.  The contrast is intended to illustrate the distinction between representational theories of perception and direct theories of perception.  By using an example from science (or perception written big), we illustrate in a way that is easier to see.

The design of the instrument

The design is almost the same as described in the earlier post.  There is one addition.  The mercury column in the capillary tube is directly calibrated in temperature.  That is to say, there are graduation markings on the thermometer, from which we can directly read off the temperature.

Representational measurement of temperature

As indicated in the previous post, I plan to use the measurement of temperature to illustrate some ideas about perception.  This post will give a representationalist account of measurement, as an illustration of indirect perception.

The apparatus to be used is very similar to a mercury thermometer.  I shall assume that the reader is reasonably familiar with traditional analog thermometers, and how they are used.

The design of the instrument

The thermometer uses a glass tube.  At the bottom of the tube, there is a largish bulb which can be filled with mercury.  Above the bulb, the glass tube contains only a very narrow tube of small diameter, sometimes called a capillary.

The bulb is initially filled with mercury, and the mercury extends to part way up the capillary tube.  Above the mercury, the tube is empty.  The air is pumped out, though it need not be a perfect vacuum.

The blind man and the cave

A blind man is dwelling in a cave.  He is not confined to the cave.  He can come and go as he pleases.  He lives in the cave because he has found it to be a rather congenial place, a place of shelter from the extremes of weather.  Yet he is by no means a hermit or a loner.  He enjoys his frequent walks to the nearby town where he can socialize with others.  He is an avid radio listener, and he uses the radio to keep himself well up to date on the local and national goings on.

Science and scientific theories

This is partly a comment on “The Knight’s Song, or What is a [scientific] theory?” and partly a post on my own view of science and how it differs from what philosophers of science say.

If we follow the Shannon-Weaver theory of communication, then

• we start with semantic information (the natural world, as studied by science);
• we encode that in a symbolic form (syntactic information, Shannon information, linguistic representation);
• that syntactic information can then be transmitted or recorded;
• a final receiver of the syntactic information can decode it to recover the semantic information.

With science, the method we use for symbolically encoding nature is what we call “measurement”.  This process of encoding produces the data on which science very much depends.  I also discussed this way of looking at measurement in an earlier post.

Semantics and measurement

There are many different conceptions of “information.”  The most important of those is that due to Claude Shannon, and often referred to as “Shannon Information“.  Shannon was particularly concerned with communication and with the problem of avoiding or minimizing loss of information due to transmission over an imperfect channel.

As used today, we typically think of Shannon information being transmitted as a sequence of symbols, often as a stream of binary digits. It is considered to be a theory of syntactic information, since the engineering considerations that motivated Shannon’s work are concerned with delivery of the symbols and questions of what those symbols mean is secondary and outside Shannon’s theory.