490 
POPULAR SCIENCE REVIEW. 
The first great improvement in the thermometer was made 
by the Florentine Academicians ; they substituted the expan- 
sion of a liquid for that of air, employing spirits of wine for 
the purpose, and they divided the tube of the instrument 
arbitrarily as before, by means of small dots of enamel placed 
at equal distances on it ; but inasmuch as the scales of the 
different instruments were not formed upon any fixed principle, 
the results which they furnished did not admit of direct com- 
parison. To obviate this evil, Newton, taking advantage of 
Hooke's observation, that ice always melted at a fixed tem- 
perature, and that, under certain standard circumstances, the 
boiling-point of water was invariable, proposed the adoption 
of these as starting-points, between which, and on either side 
of which, a scale of equal parts should be graduated as required. 
Though these two points were unanimously agreed upon as 
the points of reference to be employed, it unfortunately happens 
that the interval has been subdivided differently in different 
countries. In Great Britain, Holland, certain of the States of 
Germany, and North America, the interval between the freezing 
and the boiling points is divided into 180 equal parts or ther- 
mometric degrees. The scale is prolonged by additional equal 
parts above the boiling and below the freezing points. The 
zero is placed at the thirty-second division below the latter, so 
that on this scale the freezing-point is 32° and the boiling-point 
212° (32 + 180 = 212). This method of graduation, known as 
Fahrenheit's, was adopted about 1724. It may be remarked 
in passing that the reason why the zero was placed at 32° 
below the freezing-point, was because that point indicated the 
lowest temperature then known to exist, namely, the most 
intense cold which had been observed at Iceland. Tempera- 
tures very much lower than this, both natural and artificial, 
have been observed in more recent times. 
In France, Sweden, and other parts of Europe, the centigrade 
division introduced by Celsius prevails. In this scale, the 
interval between the two reference-points is divided into 
100°, and the zero is placed at the freezing; temperatures 
below this being indicated by the prefix of the negative 
sign. 
A system known as Reaumur's is used in Russia and parts 
of Germany ; the interval between the reference-points is 
divided into 80°. In another scale, formerly used in Russia, 
and known as De L'Isle's, from its having been invented by 
that physicist in 1733, the before-mentioned interval was 
divided into 150° reckoned backwards from the boiling-point. 
Since the number of degrees into which the interval between 
the freezing and the boiling points in the four systems is 
divided, are respectively 180, 150, 100, and 80, it follows that 
