STEAM 
ENGINE. 
cistern of mercury. These were so perfectly freed from air, 
that the column of mercury in the tube was 34 inches high ; 
when it was violently shaken, the mercurial column suddenly 
descended, and settled at 28-75 inches. Upon being in¬ 
clined, a speck of air still remained ; but when it was com¬ 
pressed by a pillar of mercury 27 inches high, this speck was 
not larger than a pin’s head. When the tube was perpendi¬ 
cular, the mercury stood at 28-75 inches; and the column of 
water above it was about 6J inches, which is equal to half an 
inch of mercury. As the whole was 29 25 inches when the 
stationary barometer stood at 29-4, the difference, or pillar 
supported by the elasticity of the steam, was equal to 0-15 
inch. The water in the pan was heated slowly by a lamp, 
and was stirred continually with a feather to distribute the 
heat equally throughout. By these means experiments were 
made from 55° to 196°-5 of temperature. 
To determine the higher degrees of elasticity, Mr. Watt in¬ 
troduced a tube, 55 inches long, through a hole in the lid of 
a digester, and within the digester it terminated in a cistern 
of mercury. A thermometer was applied, as in the experi¬ 
ments of Professor Robison, and the digester was half filled 
with water, and heated by a lamp. This caused the air in 
the upper part of the digester to expand, and although a con¬ 
siderable quantify was allowed to escape, and the water 
heated to ebullition, still some remained, for the mercury 
stood at 213§°. Dissatisfied, however, with these experi¬ 
ments, Mr. Watt, in 1796, requested Mr. Southern to repeat 
them. The results clearly proved the accuracy of Mr. 
Watt. 
Dr. Ure has thus detailed his experiments: “ fig. 3 repre¬ 
sents the construction employed for temperatures under and 
a little above the boiling point. Figs. 4 and 5 are used for 
higher temperatures; and the last is the most convenient, 
One simple principle pervades the whole train of experiments, 
which is, that the progressive increase of elastic force deve¬ 
loped by heat from the liquid, incumbent on the mercury at 
l l' l", is measured by the length of column which must be 
added over L, the primitive level below, in order to restore 
the quicksilver to its primitive level above, at /. These two 
stations, or points of departure, are nicely defined by a ring 
of fine platina wire twisted firmly around the tube. 
“ At the commencement of the experiment, after the 
liquid, well freed from air, has been let up, the quicksilver is 
made a tangent to the edge of the upper ring, by cautiously 
pouring mercury in a slender stream into the open leg of the 
syphon D. The level ring below is then carefully adjusted. 
“ From the mode of conducting these experiments, there 
remained always a quantity of liquid in contact with the 
vapour, a circumstance essential to accuracy in this research. 
“ Suppose the temperature of the water or the oil in A to 
be 32° F., as denoted by a delicate thermometer, or by the 
liquefaction of ice ; communicate heat to the cylinder A by 
means of two Argand flames playing gently on its shoulder 
at each side. When the thermometer indicates 42°, modify 
the flames, or remove them, so as to maintain an uniform 
temperature for a few minutes. A film, or line of light, will 
now be perceived between the mercury and the ring at /, as 
is seen under the vernier of a mountain barometer when it is 
raised a few feet off the ground. Were the tube at / and L 
of equal area, or were the relation of the areas experimentally 
determined, then the rise of the quicksilver above L would be 
one half, or a known submultiple of the total depression, 
equivalent to the additional elasticity of the vapour at 42° 
above that at 32°. Since the depressions, however, for 30 or 
40 degrees in this part of the scale are exceedingly small, one 
half of the quantity can scarcely be ascertained with suitable 
precision, even after taking the above precautions; and be¬ 
sides the other sources of error, or, at least, embarrassment, 
from the inequalities of the tube, and from the lengthening 
space occupied by the vapour, as the temperature ascends, 
render this method of reduction very ineligible. 
“ By the other plan we avoid all these evils. For what¬ 
ever additional elasticity we communicate to the vapour 
above l, it will be faithfully represented and measured by the 
551 
mercurial column which we must add over L, in order to 
overcome it, and restore the quicksilver under / to its zero or 
initial level, when the platina ring becomes once more a 
tangent to the mercury. 
“ At E a piece of cork is fixed, between the parallel legs of 
the syphon, to sustain it, and to serve as a point by which the 
whole is steadily suspended, 
“ For temperatures above the boiling point, the part of the 
syphon under E is evidently superfluous, merely containing 
in its two legs a useless weight of equipoise mercury. Ac¬ 
cordingly, for high heats, the apparatus figs. 4 or 5 is em¬ 
ployed, and the same method of procedure is adopted. The 
aperture at O, fig. 5, admits the bulb of the thermometer, 
which rests as usual on l". The recurved part of the tube is 
filled with mercury, and then a little liquid is passed through 
it to the sealed end. Heat is now applied by an Argand 
flame to the bottom of C, which is filled with oil or water; 
and the temperature is kept steadily at 212° for some minutes. 
Then a few drops of quicksilver may require to be added to 
D" till L" and l" be in the same horizontal plane. The fur¬ 
ther conduct of the experiment differs in no respect from what 
has been already described. The liquid in C is progressively 
heated, and at each stage mercury is progressively added over 
L" to restore the initial level, or volume at by equipoising 
the progressive elasticity. The column above L" being mea¬ 
sured, represents the succession of elastic forces. When this 
column is wished to extend very high, the vertical tube re¬ 
quires to be placed for support in the groove of a long 
wooden prism. 
“ The height of the column in some of the experiments 
being nearly 12 feet, it became necessary to employ a ladder 
to reach its top. It was found to be convenient in this case, 
after observing that the column of vapour had attained its 
primitive magnitude, to note down the temperature with the 
altitude of the column ; then immediately to pour in a mea¬ 
sured quantity of mercury nearly equal to three vertical 
inches, and to wait till the slow progress of the heating again 
brought the vapour in equilibrio with this new pressure, 
which at first had pushed the mercury within the platina ring 
at l". When the lower surface of the mercury was again a 
tangent to this ring, the temperature and altitude were both 
instantly observed. This mode of conducting the process 
will account for the experimental temperatures being very 
often odd and fractional numbers. They are therefore pre¬ 
sented to the public as they were recorded on the instant. 
“ After bestowing the utmost pains in repeating the expe¬ 
riments during a period of nearly two months, it was found 
that the only way of removing the little discrepancies which 
crept in between contiguous measures, was to adopt the 
astronomical plan of multiplying observations and deducing 
truth from the mean. It is essential to heat with extreme 
slowness and circumspection the vessels ABC. One repeti¬ 
tion of the experiment occupies, on an average, seven hours.” 
A surprising- accordance is perceived in the numbers 
between 32° and 212, given by Dr. Ure and by Mr. Dalton, 
though the experiments were performed with different appa¬ 
ratus. This accordance is of course strong proof of the cor¬ 
rectness of the results obtained. 
The experiments of Mr. Philip Taylor were made with a 
strong boiler, furnished with the required thermometer and 
barometer. During the ascent of the mercurial column of 
the thermometer, and the corresponding descent of the baro¬ 
meter, the indications of temperature and elasticity were 
accurately noted; and when the steam had attained 320°, it 
was allowed gradually to subside, and the states of tempera¬ 
ture and elasticity again ascertained. Thus a mean result 
was obtained, which is essential to great accuracy; for between 
the alternate ascents and descents of the mercurial columns 
there is some variation. 
To save the trouble of continual reference to tables; 
as well as to obviate the necessity of numerous experi¬ 
ments, it has been attempted to construct formulae by 
which the properties of unknown temperatures may be 
deduced from such as are known. In the first instance, 
Dalton, 
