Remark by the Quizmaster General
Although named after Italian physicist Galileo
Galilei, the Galilean thermometer was not
invented by him. Galileo did invent a
thermometer, called Galileo's air thermometer
(more accurately termed a thermoscope), in or
before 1603. The so-called 'Galileo thermometer'
was invented by a group of academics and
technicians known as the Accademia del Cimento
of Florence, who included Galileo's pupil,
Torricelli and Torricelli's pupil Viviani. Details of
the thermometer were published in the Saggi di
naturali esperienze fatte nell'Academia del
Cimento sotto la protezione del Serenissimo
Principe Leopoldo di Toscan e descrittedal
segretario di essa Accademia (1666), the
Academy's main publication. The English
translation of this work (1684) describes the
device ('The Fifth Thermometer') as 'slow and
lazy', a description that is reflected in an
alternative Italian name for the invention, the
termometro lento (slow thermometer). The outer
vessel was filled with 'rectified spirits of wine' (a
concentrated solution of ethanol in water); the
weights of the glass bubbles were adjusted by
grinding a small amount of glass from the sealed
end; and a small air space was left at the top of
the main vessel to allow 'for the Liquor to rarefie'
[i.e. expand].

The device now called the Galileo thermometer
Galilean Thermometer
Quiz #469 Results
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Answers to Quiz #469- March 15, 2015
1. What is the name of this device?
2. What is its purpose?
3. Why is it better to use alcohol than water?
1.  A Galilean thermometer.
2.  It measures temperature.
3.  The density of alcohol varies more with temperature
than the density of water.
This makes it more sensitive to temperature changes than water.
Comments from Our Readers
According to the Wikipedia article, Galileo did not invent this. His students did.
Rebecca Bare
The numbers with degree sign on tags indicated that the imaqe was of a
thermometer of some sort. Googled images of "glass thermometers". One image
showed partial image similar to above image. It was a Galileo Thermometer. When I
googled "Galileo Thermometer" many images similar to above came up. Wikipedia
article on the Galileo Thermometer gives a very good explanation of how it works.
Tony Knapp
Tried many image names with no success. Glass balls in water brought up Galalio's
Thermometer. Wikipedia explained device. Glass balls have constant density. Tags
show temperature at which hey will be suspended. Lower temperature balls sink,
higher temperature balls rise. Nothing suspended, temperature is between highest
singer and lowest floater. Tags on lowest show 64 and 68 assume  degrees, all
tags probably 4 degrees apart. Highest sinker 72 lowest floater 76. Measured
temperature probably around 74.
Arthur Hartwell
I'm taking a short break from trying to build ads for our orchestra's season
program. Glad I recognized the device, so I didn't get distracted from my task for
too long! Reminds me of why I always loved science, and gives me twinges of not
regret, exactly perhaps wistfulness that I didn't pursue a science or two as a
vocation. Ah, well, life has had its complications.
Peter Norton
National Geographic model: "Displays temperatures in Fahrenheit in 2 increments
from 68 to 80. Accurate to within 2. This would limit itself at my house.  I like the
temp lower then 68 in summer.  I like a customer review:

Fun to watch. Tells The Temp

NOT VERY STABLE, will break if dropped

Best Uses
Tell Temp
Very pretty

Comments about 17-inch Galileo Thermometer:
This is a beautiful piece of art that also tells the temp. You just have to put it
somewhere where it will not get knocked over and our of the reach of kids. I love
the product and would purchase another one.

BOTTOM LINE Yes, I would recommend this to a friend

Buy for decorating more than function.

I was going to buy one of these for my son and wife for Christmas, but decided
that it would not last long around a 6 year old and 2 cats.  I don't think it would be
too practical in my own home as the temps are only between 68 and 80.  I just
threw away the information last week.  Quite a coincidence that you picked it for
this week's quiz.
Judy Pfaff
These thermometers can be very beautiful. Obviously they are not precision
temperature instruments, but more decorative.
Roger Lipsett
The density of alcohol varies more than water. Also the freezing level is lower so
you wouldn't worry about it expanding and breaking the tube in Renaissance Italy.  
You could also make a cocktail if desperate.
Nelsen Spickard
N.B.  Yes, just don't swallow the glass bubbles. - Q. Gen.
I just saw somewhere that the more accurate term for this device would be a
thermoscope as opposed to a thermometer, as this device did not have a numerical
temperature scale.
Cindy Costigan
How could they put a scale on it without already having a thermometer to
measure what temperature it was?  Kind of like making pickles by soaking
cucumbers in pickle juice. - Q. Gen.
My sister actually has one like this on her kitchen window sill!
Elaine C. Hebert
When I was in grade school, we covered temperature and thermometers, and were
told that mercury was used in order to make them small, due to its extremely high
density, and that water ones were better because they were more precise..... but

This image somehow reminded me of that, and once I zoomed in and saw the
numbers and the degree sign, I figured it had to be a water thermometer, so
that's what I googled and voila. Turns out this one works in a different
principle than the mercury one and uses buoyancy to indicate the temperature, and
that Galileo didn't invent it. Looks like a great thing to have in my dream house
Ida Sanchez

Congratulations to Our Winners!

Rebecca Bare                Tynan Peterson
Tony Knapp                Arthur Hartwell
Margaret Paxton                Owen Blevins
Peter Norton                Angel Esparza
Gary Elder                Judy Pfaff
Roger Lipsett                Betty Chambers
Brett Robinson                Cynthia Costigan
Nelsen Spickard                Barbara Battles
Elaine C. Hebert                Ellen Welker
Edna Cardinal                Carol Farrant
Ida Sanchez                Debbie Johnson
Janice M. Sellers                John Thatcher

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What I find interesting is that the density of the glass bubbles
doesn't change with temperature because they are fixed size.  
Only the density in the tube changes.

This means that the liquid in the tube (and hence maybe the tube
itself) can expand and that the tube itself is not a fixed size.

I think the reason the bubbles don't change size but the tube does
is because the tube is surrounded by air, but the bubbles are
surrounded by a liquid.  The slight changes in the size of the
bubbles that would normally occur doesn't happen because the
pressure of the liquid around them prevents it.

Colleen Fitzpatrick PhD
Quizmaster General
was revived in the modern era by the National History Museum, London, which started
selling a version in the 1990s.

A simple, fairly accurate thermometer, the Galilean thermometer it is mostly used today
as decoration. The Galileo thermometer consists of a sealed glass tube that is filled with
water and several floating bubbles. The bubbles are glass spheres filled with a colored
liquid mixture. This liquid mixture may contain alcohol, or it might simply be water with
food coloring. Since the density of alcohol is more affected by changes in temperature
than the density of water, alcohol is commonly used as the liquid in a Galilean

Attached to each bubble is a little metal tag that indicates a temperature. A number and
degree symbol are engraved in the tag. These metal tags are actually calibrated
counterweights. The weight of each tag is slightly different from the others. Since the
bubbles are all hand-blown glass, they aren't exactly the same size and shape. The
bubbles are calibrated by adding a certain amount of fluid to them so that they have the
exact same density. So, after the weighted tags are attached to the bubbles, each differs
very slightly in density (the ratio of mass to volume) from the other bubbles, and the
density of all of them is very close to the density of the surrounding water.
An object immersed in a fluid experiences two major forces: the downward pull of
gravity and the upward push of buoyancy. It is the downward force of gravity that
makes this thermometer work.

The basic idea is that as the temperature of the air outside the thermometer changes, so
does the temperature of the water surrounding the bubbles. As the temperature of the
water changes, it either expands or contracts, thereby changing its density. So, at any
given density, some of the bubbles will float and others will sink. The bubble that sinks
the most indicates the approximate current temperature.

Consider this example:

Let's say there are five bubbles in the thermometer:
•A red bubble that represents 23 degrees
•A green bubble that represents 24 degrees
•A orange bubble that represents 25 degrees
•A blue bubble that represents 26 degrees
•A yellow bubble that represents 27 degrees

The red bubble (23 degrees) is the heaviest (densest) bubble, and each bubble thereafter
is slightly lighter, with the yellow bubble being the
lightest. Now, let's say the temperature in the room is
25 degrees C. Since the surrounding air is 25
degrees, we know the water inside the thermometer
is also about 25 degrees. The red and green bubbles
(23 and 24 degrees, respectively) are calibrated so
that they have higher densities than the water at this
temperature, so they sink. The blue and yellow
bubbles each have a density that is lower than the
surrounding water, so they float at the very top of
the thermometer. Since the orange bubble is
calibrated to represent 25 degrees C, the same
temperature as the water, it sinks slightly so that it is
floating just below the blue and yellow bubbles --
thereby indicating the room's temperature!
Other Types of Thermometers
- How Does an Ear Thermometer Work?
It turns out that the eardrum is an extremely accurate point to
measure body temperature from because it is recessed inside the
head (just like your tongue). The problem with the eardrum is that it
is so fragile. You don't want to be touching the eardrum with a

This makes the detection of the eardrum's temperature a remote
sensing problem. Granted, it is not very remote -- just a centimeter
or so. But it's remote nonetheless! It turns out that the remote
sensing of an object's temperature can be done using its infrared radiation. This
technique is a very good way to detect the temperature of a person's eardrum.

All of the objects around you are radiating infrared energy right now. Human beings
don't have any sensors that can detect subtle differences in infrared, but our skin can
detect objects radiating lots of infrared energy. When you warm yourself by standing
close to a fire, the "warmth" is infrared energy that you are absorbing. The idea behind
the temperature sensor in the ear thermometer is to create a device that is sensitive to
very subtle changes in infrared emission. One common sensor is the thermopile, which
can be accurate to a tenth of a degree. The thermopile sees the eardrum and measures
its infrared emissions. The emission is converted into a temperature and displayed on an