the hottest or coldest day of the year, like the Floren-
tine models. Mercury also had a much wider tempera-
ture range than alcohol. The choice of mercury as a
benchmark was contrary to the common thought at the
time, promoted by Halley as late as 1693, who believed
that mercury could not be used for thermometers
because of its low coefficient of expansion.
Fahrenheit later adjusted his temperature scale to
ignore body temperature as a fixed point, bringing the
scale to just the freezing and boiling of water. After his
death, scientists recalibrated his thermometer so that
the boiling point of water was the highest point, chang-
ing it to 212 degrees, as Fahrenheit had earlier indicat-
ed in a publication on the boiling points of various
liquids. The freezing point became 32 degrees, and
body temperature became 98.6 degrees. This is the
scale that is presently used in thermometers in the Unit-
ed States and some English-speaking countries,
although most scientists use the Celsius scale.
By 1779 there were some 19 different scales being
used for thermometers, but it was Fahrenheit, along
with astronomer ANDERS CELSIUSand Jean Christin—
whose scales were presented in 1742 and 1743—who
helped finally set the standards for an accurate ther-
mometer that are still used today. Besides making ther-
mometers, Fahrenheit also was the first to show that
the boiling point of liquids varies at different atmo-
spheric pressures, and he suggested this as a principle
for the construction of barometers. Among his other
contributions were apumping device for draining the
Dutch polders and a hygrometer for measuring atmo-
spheric humidity.
Fahrenheit died on September 16, 1736, in The
Hague at the age of 50 years. There is virtually no one
in the English-speaking countries today who does not
have a thermometer with his initial (F) on it.
See alsoCELSIUS SCALE.
family The taxonomic category between order and
tribe, but if no tribe exists, then it is the category
between order and genus. Also a social unit related by
marriage, descent, or kinship.
farsightedness A condition in eyesight where distant
objects can be seen better than objects that are closer. It
is the inability of images to focus properly on the retina
ofthe eye. The eye is too short or the cornea is too flat,
so that the images focus beyond the retina and cause
close objects to appear blurry. Also called hyperopia or
presbyopia, when the lens of the eye begins to lose elas-
ticity (normal aging process).fat (general) Any substance made up of lipids or fatty
acids that supply calories to the body and can be found
in solid or liquid form (e.g., margarine, vegetable oil);
three fatty acids linked to a glycerol molecule form fat.fat(triacylglycerol) Triacylglycerols are storage lipids,
comprising three fatty acids attached to a glycerol
molecule, found mostly stored in adipose (fat) cells and
tissues. They are highly concentrated regions of
metabolic energy. Because there are abundant reduced
CH groups available in fats for oxidation-required
energy production, they are excellent storage contain-
ers of energy. Fats can be found in plants, animals, and
animal plasma lipoproteins for lipid transport. Former-
ly known as triglyceride.fatty acid Fatty acids are the components of two
lipid types mostly found in cells in the formof large
lipids or small amounts in free form: storage fats and
structural phospholipids. They consist of long hydro-
carbon chains of varying length (from four to 24
carbon atoms), containing a terminal carbonyl group
at one end and may be saturated (has only a single
carbon-to-carbon bond) or unsaturated (one or more
double or triple carbon-to-carbon bonds). The number
and location of double bonds also vary for the different
fatty acids. More than 70 different kinds have been
found in cells. Saturated fatty acids have higher levels
of blood cholesterol, since they have a regulating effect
on its synthesis, but unsaturated ones do not have that
effect and thus they are more often promoted nutrition-
ally. Some fatty acids are palmitic acid, palmitoleic
acid, alpha-linolenic acid, eleostearic acid, linoleic acid,
oleic acid, and elaidic acid. Three fatty acids linked to a
glycerol molecule form fat.fauna All wild birds and all wild animals (both
aquatic and terrestrial); includes wild mammals, reptiles,fauna 125