THE MERCURIAL THERMOMETER The principle of the mercurial thermometer is that mercury when heated expands more than glass. If, therefore, a glass-tube having a bulb blown at one end be partially rilled with mercury and immersed in a bath at a higher temperature than its own, the mercury will rise in the tube. If the bath have a lower temperature, the mercury will fall. If the mercury neither rise nor fall we may fairly conclude that the mercury and the bath are each at the same temperature.
The essential features of a good thermometer are that it must be easily portable; permanent; always give the same reading when subjected to the same temperature; render it possible for the user to test the correctness of its graduation and determine any errors in its graduation; and be relatively small, so that when placed in contact with a second body the temperature of the second body will not be seriously affected.
In making a thermometer which will satisfy these conditions, the peculiar advantages of mercury are that it is easily prepared in a pure state; does not wet glass or stick to it; expands rapidly with changes of temperature, so that its changes in volume are easily read; that to each particular volume corresponds a definite temperature, which is not the case with water; and that it does not freeze except at temperatures comparatively low, and does not boil except at temperatures comparatively high.
Theory of heat From Wikipedia, the free encyclopedia Jump to: navigation, search In the history of science, the theory of heat or mechanical theory of heat was a theory, introduced predominantly in 1824 by the French physicist Sadi Carnot, that heat and mechanical work are equivalent.  It is related to the mechanical equivalent of heat. Over the next century, with the introduction of the second law of thermodynamics in 1850 by Rudolf Clausius, this theory evolved into the science of thermodynamics.
In 1851, in his “On the Dynamical Theory of Heat”, William Thomson outlined the view, as based on recent experiments by those such as James Joule, that “heat is not a substance, but a dynamical form of mechanical effect, we perceive that there must be an equivalence between mechanical work and heat, as between cause and effect. ”  In the years to follow, the phrase the “dynamical theory of heat” slowly evolved into the new science of thermodynamics.
In 1876, for instance, American civil engineer Richard Sears McCulloh, in his Treatise on the Mechanical Theory of Heat, stated that: “the mechanical theory of heat, sometimes called thermo-dynamics, is that branch of science which treats of the phenomena of heat as effects of motion and position. ” This term was used in 19th centuries to describe a number of laws, relations, and experimental phenomenon in relation to heat; those such as thermometry, calorimetry, combustion, specific heat, and discussions as to the quantity of heat released or absorbed during the expansion or compression of a gas, etc.
One of the most famous publications, in this direction, was the Scottish physicist James Clerk Maxwell’s 1871 book Theory of Heat, which introduced the world to Maxwell’s demon, among others.  Another famous paper, preceding this one, is the 1850 article On the Motive Power of Heat, and on the Laws which can be deduced from it for the Theory of Heat by the German physicist and mathematician Rudolf Clausius in which the concept of entropy began to take from. 4] The term “theory of heat”, being associated with either vibratory motion or energy, was generally used in contrast to the caloric theory, which views heat as a fluid or a weightless gas able to move in and out of pores in solids and found between atoms. In an 1807 journal of Nicholson’s, as an example, we find: “…it is well known that Count Rumford adheres to the old theory of heat being simply a vibratory motion of the particles of bodies. ” However, both these viewangles are actually compatible under the principle of energy conservation and corresponding first law of thermodynamics.
From modern perspective, the formal equivalence of heat and mechanical vibrations (or motions) does not mean they are physically identical. The fundamental difference of these two concepts shows particularly clearly in spectroscopy. While sharp spectral lines are usually associated with mechanical vibrations, the heat shows only a “random” spectrum with some distribution function (white noise, etc. )[ Electronic Electronic clinical thermometers
Since compact and inexpensive methods of measuring and displaying temperature became available, electronic thermometers (often called digital, because they display numeric values) have been used. Many display readings to great precision (0. 1 °C or 0. 2 °F, sometimes half that), but this should not be taken as a guarantee of accuracy: specified accuracy must be checked in documentation and maintained by periodical recalibration. A typical inexpensive electronic ear thermometer for home use has a displayed resolution of 0. 1 °C, but a stated accuracy within ±0. 2 °C when new.