| 
448 TIDES. 
motion round the earth, while the earth, turn- 
ing on its axis, causes any given place to pass 
through each of these swells and the intervening 
| depressions in a lunar day, or twenty-four hours 
| fifty minutes. What we have said with respect 
to the moon’s influence in disturbing the level 
of the ocean, may be applied also to that of the 
sun; only, in the case of the sun, although its 
absolute action is about double that of the moon, 
yet. on account of its very great distance, its re- 
lative action upon the surface of the earth, com- 
pared with that at the centre, is but about one 
third as great as that of the moon. At new and 
full moon, when the sun’s and moon’s actions 
conspire, the tides are highest, and are called 
spring tides. But at the first and last quarters 
of the moon, the action on one body tends to 
counteract that of the other; and the tides, both 
| at ebb and flow, are smallest, and are called neap 
tides. We have supposed the highest tides to 
| happen at new and full moon, and the lowest at 
_ the quarters. But the waters do not yield in- 
| stantly to the action exerted upon them; the 
greatest effect takes place some time after the 
| attractive influence has passed its point of great- 
est power. Thus the spring and neap tides ac- 
tually occur about a day and a half after the 
| times above indicated. So, also, for a similar 
_ reason, the real time of high water, in the daily 
| tides, happens about three hours after the moon 
| has passed the meridian. 
It will be perceived, from what has been said, 
that the sun’s and moon’s influence will vary 
with a change of distance, being greatest when 
the attracting body is nearest, and vice versa. 
The phenomena of the tides are modified, more- 
over, by the situation of the sun and moon with 
respect to the equator, and the particular lati- 
tude of the observer. When, for instance, the 
moon passes near the zenith of the observer, sup- 
posed to be in one of the temperate zones, the 
opposite high tide will be in the same latitude 
on the other side of the equator; consequently, 
under the above circumstances, the high tide, 
when the moon is above the horizon, exceeds the 
high tide when the moon is below the horizon; 
and at a point in the direction of the nearest 
pole, fifty degrees from the place where the moon 
| is vertical, there will be only one tide in twenty- 
four hours. The different heights to which the 
same tide rises, in places but little distant from 
each other, depend upon local circumstances; as 
the particular form of the coast, the meeting of 
currents, &c. Where a bay grows narrower and 
narrower, like a tunnel, as it runs up from the 
ocean into the land, the swell of water must rise 
higher as the passage becomes more contracted 
in breadth. Thus, in the bay of Fundy, which 
answers to this description, and is of great ex- 
tent, the tide sometimes rises to the height of 
seventy feet. It is frequently asked, why there 
are not tides in the inland seas and larger lakes. 
If we observe, upon an artificial globe, the very 
a re 
small space occupied by the largest bodies of 
water of this description, we shall readily perceive 
that there can be no appreciable difference in 
the action of the moon upon so small a portion 
of the earth’s surface; the whole of the lake, or 
over it, and there is no heavier mass of water 
ninety degrees distant to force it above its natu- 
ral level. 
TIGER-FLOWER,—botanically Tigridia. A | 
small genus of hardy, bulbous-rooted, herbaceous, 
magnificently-flowering, Mexican plants, of the 
iris order. 
nia, called by Linneus Ferraria tugridia, was 
introduced to Britain in 1796, and is well known 
to all amateur florists as one of the most gorgeous 
glories of the parterre. Its bulb is tunicated, 
and of smaller size than that of the common nar- 
cissuses ; its leaves rise from the root-crown, and 
are lanceolate, channelled, erect, large, and of a 
bright green colour; its floral footstalks rise from 
among the leaves to the height of about 10 or 12 
inches; and its flowers are as large as those of 
the largest irises or lilies, and display the most 
brilliant mixtures and spottings of orange and 
red, in the manner of the tiger’s skin, and are so 
startling and superb as, at the very first glance, 
to astonish and delight even the most apathetic 
observers, and may be made to bloom in succession 
from May till September, but are individually 
among the most evanescent of sublunary gran- 
deurs, and last each during only a part of one 
day, and scarcely unfold their magnificence to 
the sun or the breeze till they begin to wither 
and die. A variety called the lion-flower, 7. p. 
leona, and a species called the shell-flowered ti- 
gridia, 7. conchiiflora, were introduced in 1823; | 
and the latter has a predominance of dark yellow 
in its corolla, and is scarcely less beautiful than 
the normal tiger-flower, yet does not display the 
same diversity and depth and brilliancy of tints. 
All the three kinds love a soil of sandy peat, and 
are propagated from offsets, and may be grown | 
in clumps or beds of the open ground, in the 
same manner as any other hardy bulbous-rooted 
bloomers. The common treatment is to cut 
down the stems and take up the bulbs in autumn, 
and to replant the latter in a dried state in 
spring; but a much better one is to lift the 
plants in autumn with balls or masses of attached 
soil, to put them in pots of sufficient capacity to 
admit the attached balls, and to keep these in a 
cold pit till the time of replanting in spring. 
TIGLIUM. See Croton. 
TIGRIDIA. See Trgur-F Lower. 
TILE. A thin brick fabric, either flat, undu- 
lated, semi-cylindrical, tubular, or of any other 
form. Tiles of various kinds have, in recent 
times, come into very extensive use in georgy as 
materials of subsoil drains; and, in consequence, 
possess great interest to all persons who have any 
sort of connexion with agriculture,—and very 
eminently to farmers and landed proprietors. A 
sea, therefore, becomes lighter when the moon is | | 
| 
t 
The peacock species, Zigridia pavo- | 
