T EM 



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TEN 



the nebular hypothesis be correct, or 

 otherwise, it certainly does appear 

 that a very high temperature did 

 once exist on this planet; and that 

 such temperature has been gradu- 

 ally diminishing. "Whether also 

 the nucleus of the globe be in a state 

 of incandescence or fusion is a ques- 

 tion which probably never will be 

 solved, till the heavens shall be 

 rolled away as a curtain, and the 

 elements shall melt with fervent 

 heat. Still we well know that the 

 temperature of the earth does 

 increase in a fixed and certain 

 ratio as we descend into its depths. 

 The following are general results 

 from the various facts observable 

 on the earth's surface, and such 

 depths thereof as man has hitherto 

 been able to penetrate. 1 . Nume- 

 rous experiments in mines shew an 

 increase of temperature from the 

 surface downwards, that is, from 

 those depths where the action of 

 the solar rays ceases to produce a 

 variable heat. 2. Thermal springs 

 occur in all parts of the world, 

 and among all varieties of rock. 

 3. The temperature of the water 

 in Artesian wells is found to in- 

 crease with the depth. 4. Terrestial 

 temperature, at small depths, does 

 not coincide with the mean tem- 

 perature of the atmosphere above 

 it. 5. Igneous matter has been 

 ejected at all periods from the inte- 

 rior of the earth. 6. Active vol- 

 canoes occur widely spread over the 

 surface of the world, and so closely 

 resemble each other, that they may 

 be considered as produced by a 

 common cause, and that cause 

 deep-seated. 7. Geological phe- 

 nomena attest a great decrease of 

 temperature on the surface of the 

 globe. 8. A decreased tempera- 

 ture of the earth would, by radia- 

 tion, produce the various mountain 

 ranges and fractured strata found 

 on the surface of our planet. 

 When all these circumstances are 



taken into consideration, and we 

 add the probability that heat coun- 

 teracts the effects of gravity in the 

 sun and certain planets, and that 

 the free passage of the particles of 

 terrestrial matter among each other 

 was necessary to produce the figure 

 of the earth, the evidence in favour 

 not only of a central heat at pre- 

 sent, but also of a heat of far 

 greater intensity at remote geolo- 

 gical epochs, becomes exceedingly 

 strong; so strong, indeed, that 

 there is some difiiculty in resisting 

 the impression that we have, by 

 various means, made as fair an 

 approximation to the truth, as the 

 nature of the subject will admit. 

 If the theory of central heat be 

 founded on probability, the very 

 general occurrence of tilted and 

 fractured rocks is of easy explana- 

 tion. From a series of experiments, 

 it appears that the temperature of 

 the earth's crust increases at the 

 rate of 1 Fahrenheit for every 

 forty-five feet of perpendicular 

 descent. 



TE'NDKIL. (tendron, Fr.) In botany, 

 a spiral appendage to certain plants, 

 its use being to clasp and wind 

 round other bodies, by which means 

 weak and climbing stems support 

 themselves, and rise to a great 

 height. 



TE'NNANTITE. A variety of sulphuret 

 of copper, of a lead-grey or blackish 

 colour, thus named by Prof. Phil- 

 lips. It occurs in copper veins in 

 some of the mines of Cornwall. Its 

 constituents are, according to the 

 analysis of Prof. Phillips, copper 

 45-32, arsenic 11'84, iron 9-26, 

 sulphur 28-74, silica 5'00. Hard- 

 ness 4-0. Specific gravity from 

 4'3 to 4-4. It occurs massive, and 

 crystallized in rhomboidal dodeca- 

 hedrons, cubes, and octohedrons. 



TE'NTACLES. j Feelers ; exploring or- 



TENTA'CULA. j gans. In its most 

 restricted sense this term is under- 

 stood to signify organs, appendages 



