The symbol is used throughout to indicate per cent.

The French Millimetre (mm) equals 0.03937 English inch. 762 mm = 30 Eng. in., or more correctly 29.9999.

The Metre (m) equals 39.37100 Eng. in., or 3.28089 feet.

The Toise equals 1.949036 metres, or 6.39495 Eng. feet.

The old Paris Foot equals 1.06578 foot Eng.

The Gramme equals 15.438 gr. troy.

To convert centigrade degrees into those of Fahrenheit, by mental calculation, double the former, and deduct one-tenth of the product, add 32° if the temperature is above the freezing-point, but if below it subtract the product from 32°.

7

MICROSCOPIC REPRESENTATIONS OF RED SNOW.
(Vide p. 199, § 215.)

8

Fig. I.

Fig. I. represents Red Snow of the Grimsel, magnified 300 times: Shuttleworth,-Jameson's Journal, No. 57, coloured plate.

1. Represents the general appearance of the snow, the dark patches being coloured red. 2. a, globules of Protococcus nivalis; b, a globule whence sporules have escaped; c, a globule surrounded with the Protococcus nebulosus (10),-Kutzing.

3. Astasia nivalis, Shuttleworth.

4. Gyges sanguineus,-Shuttleworth.

5. and 6. Other infusoria (coloured red).

7. and 8. Other infusoria uncoloured.

9. Monas gliscens.

Fig. II. represents the Red Snow as given by Carpenter,-Princip. of Gen. and Compar. Physiol. 2d ed. p. 76.

Protococcus nivalis,-a, a, a, vesicles or cells containing germs; b, the same ruptured; c, the liberated germs becoming developed.

b

Fig. II.

DIAGRAMS AND ENGRAVINGS.

Page 35, Graphic representation of the Barometric curve in this country.

...

54, 104,

...

104,

106,
106,

Thermometric curve in this country.
Curve of Mean Humidity in this country.
Curve of Mean Dryness in this country, com-
puted in the fall of rain, were the aque-
ous particles fully, and simultaneously,
precipitated.

Curve of Mean Dew-point in this country.
Curve of Mean Dryness in this country.

In these diagrams the indications are read off upon the vertical lines to
the right hand of the respective months.

180, Section of a remarkable hailstone, reduced one-third.
181, Drawings of hailstones, reduced one-third. The cerebral form of some
which fell, is shewn in Fig. 1; the lenticular form of others, in Fig. 2.
In the section represented in Fig. 3, a better idea will be conveyed by
supposing the radii to be formed by a series of minute air-bubbles,
which gave to the mass the stellular fibrous arrangement which it
presented.

198, 215, descriptive of red snow, illustrated by microscopic representations
at page 467.

212, Iceberg seen off the Cape of Good Hope, April 1829.

... 220, Diagram exhibiting the course of the pencils of light which produce the

rainbow.

221, Diagram representing the Primary and Secondary Rainbows.

234, Parhelia seen in England, in 1233.

by Scheiner, in 1630.

by Hevelius, in 1660.

by Hevelius, in 1661. The external circle in this drawing

represents the horizon.

by Hoff and Kries, in 1824.

in America, in 1825.

by Parry, in the Arctic Regions.

...

by Parry, on April 9. 1820-(figure to the right).

by Hevelius, March 30. 1660.

243, Paraselena

243,

...

by Hevelius, December 17. 1660.

418, Diagram representing part of the Cuba Hurricane, in illustration of the circular and progressive motion of these winds.

446, The Mountain Barometer suspended by its tripod-stand.

446, The Marine Barometer: Fig. 1, the instrument, but not suspended as it is on ship-board; Fig. 2, the mercurial tube detached.

447, Keith's Register Barometer. Upon the surface of the mercury there rests an ivory float, supporting a kneed wire which moves two delicate indices, sliding on a wire attached to the scale, which in this instrument is inverted.

447, Dr Traill's Register Barometer. The diagonal barometer to the right, registers the maximum elevation of the mercury, by pushing before it a piece of iron wire introduced into the closed end of the tube. The barometer to the left, which is a slight modification of the rectangular barometer of Cassini and John Bernoulli, indicates the minimum depression of the mercury, by leaving behind it a similar float, introduced into the open end of the instrument.

470

DIAGRAMS AND ENGRAVINGS.

Page 449, The Aneroid Barometer: Fig. 1, its external appearance; Fig. 2, its internal structure; Fig. 3 (next page), a perspective view of the

same.

451, Diagrams representing the vacuum-chamber of the Aneroid detached.
452, The Sympicsometer. To prevent oscillations from motion at sea, the bore
of the tube at the lower part is capillary.

455, Six's Register Thermometer. The elongated bulb in the centre, is filled
with alcohol, which is continued in the capillary tube till it meets
the mercury in the curved part of the instrument; the smaller
bulb is partially filled with spirit, which reaches to the mercury.
As the alcohol in the large tube expands or contracts by tempera-
ture, there is a corresponding movement of the mercury; and pro-
perly constructed indices leave indications of its position.
455, Dr Traill's Register Thermometer. This is a modification of the one de-
scribed, alcohol and mercury being employed; but its chief advan-
tage over Six's thermometer, is the more simple form of the in-
dices, springs being rendered unnecessary by the slight inclination
of the tube.

457, The Differential Thermometer.

458, Dr Lind's Portable Anemometer. When used, the tube is half-filled with water, and as it revolves freely upon the iron spindle, the kneed part is directed to the wind. The detached kneed-tube is put on when the wind is strong, allowance being made in reading off the indication. The instrument may be held in the hand, or screwed into any convenient support.

460, Professor Daniell's Hygrometer. This instrument consists of two parts,
-a stem, upon which the hygrometer, properly so called, rests,
and to which a thermometer is attached; and the glass tube
above. This tube is twice bent at right angles, and upon its ex-
tremities two balls of equal size are blown, the whole being air-
tight. The bulb upon the shorter limb is covered with muslin,
and is moistened with ether when the instrument is used. In the
other bulb and limb of the apparatus, there is a delicate thermo-
meter; this ball is darkened and partly filled with ether it is
upon it, that the dew is deposited, the earliest appearance of
which is to be carefully watched, and the temperature of both
thermometers then noted.

460, Sir John Leslie's Hygrometer, with case.
461, Leslie's Atmometer.

461, Dr Anderson's Atmometer.

462, The Ombrometer, or Rain-Gauge.
463, Leslie's Photometer.

465, Bennet's Gold-Leaf Electrometer.

465, Henley's Quadrant Electrometer.