T H Y 



[ 259 ] 



T I N 



THYRSE. } (thyrsus, Lat. Bvptrog, Gr. 



THY'RSUS. i thyrse, Fr.) In botany, a 

 kind of inflorescence, as when the middle 

 branches of a panicle are longer than the 

 others. The horse-chesnut, lilac, &c., 

 afford examples. 



TI'BIA. (tibia, Lat. tibia, Fr.) The name 

 given to the shin-bone, or large bone of 

 the leg. It is said to have received its 

 name from a supposed resemblance to a 

 pipe or flute. 



TIDE, (ebbe and fluth, Germ, fiusso del 

 mare, It.) The flow of the water in the 

 ocean ; the alternate rise and fall of the 

 surface of the sea twice in the course of 

 a lunar day, or in 24h. 50m. 28s. of solar 

 time. The tides are a subject on which 

 many persons find a great difficulty of 

 conception. As the tides depend upon 

 the action of the sun and moon, their rise 

 and fall are classed among astronomical 

 problems, of which they are the most 

 difficult, and their explanation the least 

 satisfactory. That the moon, by her at- 

 traction, should heap up the waters of the 

 ocean under her, seems to .most persons 

 very natural, that the same cause should, 

 at the same time, heap them up at the 

 opposite, appears to many a palpable 

 absurdity. Yet nothing is more true, nor 

 indeed more evident, when we consider 

 that it is not by her whole attraction, but 

 by the differences of her attractions at the 

 two surfaces and at the centre that the 

 waters are raised. In the semi-diurnal 

 tides there are two phenomena particu- 

 larly to be distinguished, one occurring 

 twice in a month, and the other twice in 

 a-year. The first phenomenon is that 

 the tides are much increased in the syzi- 

 gies, or at the time of new and full moon. 

 In both cases the sun and moon are in 

 the same meridian : for when the moon 

 is new they are in conjunction ; when she 

 is full they are in opposition. In each of 

 these positions, their action is combined 

 to produce the highest or spring-tides 

 under that meridian. The neap tides 

 take place when the moon is in quadra- 

 ture. The higher the sea rises in full 

 tide, the lower it is in the ebb. The 

 second phenomenon is the augmentation 

 in the tides occurring at the time of the 

 equinoxes, when the sun's declination is 

 zero, which happens twice every year. 

 The greatest tides take place when a new 

 or full moon happens near the equinoxes, 

 while the moon is in perigee. The height 

 to which the tides rise is much greater in 

 narrow channels than in the open sea, on 

 account of the obstructions they meet 

 with. The tides in the British channel 

 sometimes, in some parts, rise as high as 

 fifty feet ; whereas on the shores of some 

 of the islands near the centre of the Pacific 



ocean, they do not exceed one or two 

 feet. One of the most remarkable cir- 

 cumstances in the theory of the tides is 

 the assurance, that in consequence of the 

 density of the sea being only one-fifth of 

 the mean density of the earth, and the 

 earth itself increasing in density towards 

 its centre, the stability of the equilibrium 

 of the ocean can never be subverted by 

 any physical cause. A general inundation 

 arising from the mere instability of the 

 ocean is therefore impossible. Mrs. So- 

 merville. Sir John Herschel. 

 TIN. (zinn, Germ, etain, Fr. stagno, It.) 

 A metal of a white brilliant colour, slightly 

 tinged with grey, being one of the fifty- 

 five simple or elementary bodies. Its 

 specific gravity is 7*3. It fuses at a tem- 

 perature of 442 Fahrenheit. It is of 

 greater hardness than lead, but not so 

 hard as gold. It is very malleable, and 

 may be beaten out into leaves one two- 

 thousandth of an inch in thickness. It is 

 more tenacious than lead, and a wire of 

 tin one-tenth of an inch in diameter will 

 sustain a weight of forty-seven pounds. 

 It is very flexible, and, while being bent, 

 it causes a crackling noise. Tin unites 

 with many metals, forming valuable alloys. 

 The bronze of the ancients consisted of 

 88 or 90 parts of copper, with 10 or 12 

 parts of tin. Bell-metal consists generally 

 of one-fifth of tin to four-fifths of copper. 

 The gongs of the Chinese are formed of 

 one-fifth of tin and four-fifths of copper. 



Tin is mentioned repeatedly in the 

 Pentateuch. It is generally believed that 

 the Phoenicians came to Britain for tin, 

 and, from the importance of the trade, 

 that they concealed the situation whence 

 it was obtained ; it is certain that be- 

 fore the time of Herodotus tin was ob- 

 tained from Cornwall. The period at 

 which Cornish tin was first worked and 

 exported would appear to be lost in the 

 obscurity of past ages. Mr. Hawkins con- 

 siders that the Phoenician colony of Gades, 

 on the western coast of Spain, was the 

 medium or entrepot of the commercial 

 intercourse between Phoenicia and Corn- 

 wall. Diodorus says, " we will now give 

 an account of the tin which is produced 

 in Britain." The total value of tin-ores 

 sold in 1837, according to a statement 

 in Mr. De La Beche's Geological Report 

 of Cornwall, &c. amounted to .363,322 

 16*. 4d. Mr. W. Phillips states "at 

 about 80 or 100 feet under the surface, 

 the first traces of copper or tin are usually 

 found. If tin be first discovered, even 

 without a trace of copper, it is not un- 

 usual that, in the course. of sinking 80 or 

 100 feet, or more, all trace of it is lost, and 

 copper only is found ; but if, instead of tin, 

 copper be first discovered at a depth of 80 or 



