MECHANICS. 
727 
Eng. Feet. 
Source of the Nile - 8082 
Monaftery of St. Bernard, (the higheft inhabited? 
ground in Europe) - - - S ' 
Pic de los Reyes, Pyrennees - - 7 620 
Chain of Olympus - - . - 6500 
Stony Mountains in the N. W. parts of America 6200 
Elaaferk, in Old Greenland - 6000 
Mount Puy de Dome, in Auvergne - - 5088 
Mount Ida and Mount Gargara - - 49 6 ° 
Mount Hecla, in Iceland - - - 4 88 7 
Ben Nevis (higheft in Great Britain) « - 4380 
Mount Vefuvius - - 39 3 8 
Ben Lawers, Perthfhire * - - 3 ^ 5 ^ 
Ben Moir, Scotland - - 37 2 3 
Mount Mifery, St. Chriftopher’s, W. I. •> 37 11 
Snowden, Carnarvonfnire - 3555 
Cader Idris, Merionethfliire *■ 355 ° 
Ben Glee - - - -> - 347 2 
Schehallion - - 34^ 1 
Table Mountain, Cape of Good Hope - 3454 
Mount Athos, in European Turkey - - 3353 
Hartfell, Dumfrierlhire - 33°4 
Ben Lomond, Stirlingfhire - - 3108 
The Ghauts, in Hindooftan, - - 3000 
Diana’s Peak, St. Helena - - '* 2692 
Cheviot Hills, Roxburghfhire - - 2682 
Tinto - 2342 
Mount Carmel, Afiatic Turkey - - 2000 
Gibraltar, higheft point of - - 1539 
Lake of Geneva - 1232 
Cafpian Sea, below the Ocean ... 306 
This laft is fo Angular, that is necefiary to give the au¬ 
thority on which the determination is founded. It is de¬ 
duced from nine years obfervations with the barometer 
at Aftrachan by Mr. Lecre, compared with a feries of ob¬ 
fervations made with the fame barometer at Sc. Peterf- 
burgh. 
Of the Thermometer. Plate XXL 
The thermometer is an inftrument for meafuring the 
degree of heat or cold in any body. The thermometer 
was invented about the beginning of the feventeenth cen¬ 
tury ; but, like many other ufeful inventions, it has been 
found impoflible to afeertain to whom the honour of it 
belongs. Boerhaave aferibes it to Cornelius Drebbel of 
Alcmar, his own countryman. Fulgentius attributes it to 
his mailer Paul Sarpi, the great oracle of the Venetian re¬ 
public ; and Viviani gives the honour of it to Galileo. 
But all fhefe are pofthumous claims. Sanctorius claims 
this honour to himfelf; and his aftertion is corroborated 
by Borelli, and Malpighi of the Florentine academy, 
whofe partiality is not to be fufpeHed in favour of a mem¬ 
ber of the Patavinian fchool. Perhaps the bed way to 
reconcile thefe different claims would be, to fuppofe that 
the thermometer was really invented by different perfons 
about the fame time. We know that there are certain 
periods in the progrefs of the arts when the ftream of hu¬ 
man genius runs in the fame direction, and moves to¬ 
wards the fame objeft. That part of the current which 
reaches the objeH firft may pofiefs the title; but the other 
parts follow fo rapidly and arrive fo foon after, that it is 
impoflible for a fpeftator to decide which is firft in point 
of time. 
1. The firft fpecies of this inftrument for meafuring the 
degrees of heat and cold, was the air-tkermometer. It is a 
well known fa6l that air expands with heat fo as to oc¬ 
cupy more fpace than it does when cold, and that it is 
condenfed by cold fo as to occupy lefs fpace than when 
warmed,and that this expanfion and condenfation is greater 
or lefs according to the degree of heat or cold applied. 
The principle then on which the air-thermometer was 
conftrufted is very Ample. The air was conAned in a 
tube by means of forae coloured liquor; the liquor rofe 
or fell according as the air became expanded or condenfed. 
What the ftrft form of the tube was, cannot now perhaps 
4 
be well known ; but the following defeription of the air- 
thermometer will fully explain its nature. The air-ther¬ 
mometer conAfts of a glafs tube B E, (Ag. 34.) connected 
at one end with a large glafs ball A, and at the other end 
immerfed in an open veflel, or terminating in a ball DE, 
with a narrow oriAce at D ; which veflel, or ball, contains 
any coloured liquor that will not eaflly freeze. Aqua¬ 
fortis tinged of a Ane blue colour with a folution of vi¬ 
triol or copper, or fpirit of wine tinged with cochineal, 
will anfwer this purpofe. But the ball A muft be Arft 
moderately warmed, fo that a part of the air contained in 
it may be expelled through the oriAce D ; and then the 
liquor prefled by the weight of the atmofphere will enter 
the ball D E, and rife, for example, to the middle of the 
tube at C, at a mean temperature of the weather; and in 
this ftate the liquor by. its weight, and the air included 
in the ball A, &c. by its elafticity, will counterbalance 
the weight of the atmofphere. As the furrounding air 
becomes warmer, the air in the ball and upper part of the 
tube, expanding by heat, will drive the liquor into the 
lower ball, and confequently its furface will defeend ; on 
the contrary, as the ambient air becotnes colder, that in 
the ball is condenfed, and the liquor prefled by the weight 
of the atmofphere will afeend; fo that the liquor in the 
tube will afeend or defeend more or lefs according to the 
ftate of the air contiguous to the inftrument. To the 
tube is affixed a fcale of the fame length, divided upwards 
and downwards from the middle C into 100 equal parts, 
by means of which the afcent and defeent of the liquor 
in the tube, and confequently the variations in the cold oc 
heat of the atmofphere, may be obferved. This inftru¬ 
ment was extremely defeftive ; for the air in the tube 
was not only affefted by the heat and cold of the atmo¬ 
fphere, but alfo by its weight. 
2. The air being found improper for meafuring with 
accuracy the variations of heat and cold according to the 
form of the thermometer which was ftrft adopted, another 
fluid was propofed about the middle of the feventeenth 
century by the Florentine academy. This fluid was fpirit: 
of wine, or alcohol, as it is now generally named. The 
alcohol, being coloured, was incloled in a very Ane cylin¬ 
drical glafs tube, previoufly exhaufted of its air, having a 
hollow ball at one end A, Ag. 35. and hermetically fealed 
at the other end D. The ball and tube are Ailed with 
rectified fpirit of wine to a convenient height, as to C, 
when the weather is of a mean temperature, which may 
be done by inverting the tube into a veflel of ftagnant 
coloured fpirit, under a receiver of the air-pump, or in 
any other way. When the thermometer is properly Ailed* 
the end D is heated red-hot by a lamp, and then herme¬ 
tically fealed, leaving the included air of about one-third 
of its natural denftty, to prevent the air which is in the 
fpirit from dividing it in its expanfion. As fpirit of win© 
is capable of a very confiderable degree of rarefa&ion and 
condenfation by heat and cold, when the heat of the at¬ 
mofphere increafes the fpirit dilates, and, confequently 
riles in the tube ; and, when the heat decreafes, the fpirit 
defeends; and the degree or quantity of the motion is 
fhown by a fcale, as in the preceding. 
The fpirit-thermomcUr was not fubjefl to fome of the in¬ 
conveniences which attended the air-thermometer; in 
particular, it was not affefted by variations in the weight, 
of the atmofphere ; accordingly it foon came into general; 
ufe among philofophers. It was, at an early period, in¬ 
troduced into England by Mr. Boyle. To this inftru¬ 
ment, as then ufed, there are, however, many objections. 
The liquor was of different degrees of ftrength, and there¬ 
fore different tubes filled with it, when expofed to the 
fame degree of heat, would not correfpoud. There was. 
alfo another defeft: the fcale which was adjufted to the 
thermometer did not commence at any fixed point; the 
higheft term was adjufted to the great funfliine heats of 
Florence, which are too variable and undetermined ; and 
frequently the workman formed the fcale according to 
his own fancy. While the thermometer laboured under 
fuch difad vantages, it could not be of general ufe ? 
