| 45° it is 58°1°. 
with snow; and so in other deep caves. 
and at 3 feet 52°. 
| foot it varies 25° in the year, at 2 feet 20°, at 4 
| 40°. 
416 
Catacombs at Paris, the thermometer through 
the year is between 52° and 54°, while on the 
surface it varies from 90° to 0° In Mexican 
mines it stands constantly at 74°. Depths of 
undisturbed air are like water. Ina silver mine 
in Norway, 300 feet deep, the bottom is covered 
While 
the air above snow is 70° below the freezing 
point, the surface of the ground below the snow 
is only 32°. Jt has been proved by experiment 
in latitude 56° 10’, by keeping thermometers 
fixed in the ground at various depths, that frost 
does not penetrate so deep in the earth as a foot; 
that at the depths of one, two, and three feet, the 
lowest temperature, during two years, was at one 
| foot 33°, at 2 feet 36°, and at 3 feet 39°, while 
the highest was at one foot 35°, at 2 feet 52° 5’, 
By other observations at one 
feet 15°, at 8 feet 9° 5, and at 31 feet, 2° 7’; 
while at 40 or 50 there is no variation. In 
the deepest coal-mine in England, the mean an- 
_ nual temperature at 400 yards below the surface 
| is 77°, and at 300 yards 70°; while at the sur- 
| face it is but 48°, being about 1° of increase for 
every 15 yards. This explains the origin of hot 
springs, for at 3,300 yards the heat would be 
equal to boiling water, taking 20 to a degree. 
The heat of the Bath waters is:116°; hence they 
would appear to rise 1,320 yards. At great 
depths in the sea, as 4,000 feet, the difference is 
from 15° to 22° between the air and the water 
at that depth; and at 4,680 feet, the water is 
26°, while the air is 485°. By experiments made 
_ at the observatory of Paris, for ascertaining the 
increase of temperature from the surface of the 
earth towards the interior, 51 feet deep corre- 
sponds to the increase of 1°. Hence the tem- 
perature of boiling water would be at 8,212 feet 
under Paris. The mean annual temperature of 
the whole earth at the level of the sea is 50°. 
| For different latitudes, it is as under, the third 
column showing the height in feet of constant 
| freezing in those latitudes. 
Degrees. Feet. 
Equator 84°2 . 15,000 
lat. 10°. 82°6 '. .14,700 
20 781 «13,300 
30 71:1 4 11,500 
40 62°6 >: - 9,000 - 
50 53°6 Pe Can 6,300 
60 45 | 3,800 
70 38°1 1,700 
450 
The mean heat at the equator is 84:29, and at 
Of 10,000 rays falling perpendi- 
eularly, 8,100 reach the earth,—7,000 at 509, 
2,800 at 7°, and 5 at 0°: Water seldom freezes 
till the meridian altitude of the sun is less than 
When the sun is in Aries and Libra, the 
relative heat of the equator, according to Hum- 
boldt, is taken at 1,000; at 20° is 940; at 40° is 
750; and at 60° is 590. But when in Cancer or 
Capricorn, it is, for the same hemisphere, at 0°, ; coldest day in the year. 
TEMPERATURE. 
9,117; at 20°, 1,008; at 40° and 50°, 1,150; at 
70°, 1,159; and at 80° and 90°, owing to sunshine 
for six Hionthe: 1,250. 
The temperature in equal latitudes is from 4° 
to 8° less in the southern hemisphere; and this 
difference is supposed to arise from the extended 
surfaces of water, and from the sun passing 
through the southern signs 7? days less than the 
northern. The climate of the southern hemi- 
sphere is more equable than that of the northern. 
In May, at Cape Horn, latitude 56°, our Novem- 
ber vegetation is flourishing. The sea is colder 
in the south, and ice extends 400 or 500 miles 
further from the south pole than from the north. 
There are currents from the poles towards the 
tropics, and then from east to west, in conjunction 
with the trade-winds. In latitude 75°, where 
the mean temperature is only 37°, only moss, 
lichen, dwarf willow, and sorrel grow. The 
earth, from the equator to the poles, resembles 
mountains in their kinds of vegetation from the 
base to the summit. Humboldt says the pro- 
portions in variety are, in the tropics 12; tem- 
perate zones, 1; and frigid, 0°l. The cold and 
heat of climates depend also on the vicinage of 
seas.—At Moscow the thermometer ranges from 
6° to 70°, but at Copenhagen, in the same lati- 
tude, only from 27° to 65°; so at Vienna it ranges 
from 26° to 70°, but on the French coast, in the 
same latitude, only from 41° to 67. In the Gulf 
of Guinea the thermometer rises. to 130°; and 
Humboldt thinks that in the air it can never rise 
above 140°; at sea it never rises above 85° or 88’. 
The average heat at London in the first 16 years 
of this century was 50°93. The hottest day from 
1774 to 1837 was in July, 1808, being 93°5; and 
the coldest, 25th December, 1796, 2° below zero. 
In 1830, the highest point of the thermometer 
was 90° in June, and the lowest 11° in January. 
The wettest month was 2°516 in July, and the 
driest 0°746 in February. In the past century, 
the severe frosts in England were in the winters 
of 1708, 1715, 1739, called the hard frost, 1742, 
1754, 1776, 1788, 1796, and 1813. The highest 
temperature in the sun’s rays at London is 154°; 
the highest of the air in the shade 90°; the 
mean temperature of the air 493°, lowest 11°, and 
on the earth’s surface 5. In the counties round 
London, the mean temperature and rain in every 
month is as under :-— 
Degrees. Inches. 
January . 36°] 1-483 
February 380 "746 
March 43°9 1:44 
April 49°9 1°786 
May . 54°0 1°853 
June . 58°7 1:83 
July . 61-0 2-516 
August . 61°6 1:453 
September . 578 2-193 
October 48°9 2:073 
‘November 42°9 2-4 
December 39°3 2°426 
The 14th January, on an average of years, is the 
— 
The mean daily course 
a 
