TRU 



TRU 



equator at the first point of Libra, con- 

 tinues to descend southward till it 

 reaches the first point of Capricorn, when 

 it again turns to the northward and 

 reaches Aries. 



TROPICAL YEAR. The period of 

 time which intervenes between two coin- 

 cidences of the sun with the vernal equi- 

 nox. This is the common or civil year, 

 in which the phenomena of the seasons 

 are repeated, and after which they recom- 

 mence. It depends chiefly and directly 

 on the annual revolution of the earth 

 round the sun, but subordinately also, 

 and indirectly, on its rotation round its 

 own axis, which occasions the precession 

 of the equinoxes. It consists of 365d. 

 5h. 48m. 49s. 7 ; it is, therefore, shorter 

 than the sidereal year, or the period of 

 the actual revolution of the earth round 

 the sun, by 4' 39". 7. See Anomalistic 

 Year. 



TROUGH APPARATUS. Oersted's 

 trough apparatus is essentially the same 

 as WoUaston's battery. It consists of a 

 trough of copper plate, in the form of a 

 parallelopiped, about ^ an inch wide at 

 the bottom; in it the zinc plates are 

 •arranged so as not to touch the copper ; 

 the trough serves also to hold the liquid. 



TROUGH, PNEUMATIC. A vessel 

 made of tinned iron for collecting gases. 

 It has a moveable stage or bridge, above 

 which water is to be poured to the height 

 of about an inch. The bridge is perfo- 

 rated by a round hole, communicating 

 above with an inverted receiver, into 

 which it transmits the gas conveyed to it 

 by a tube beneath the surface of the 

 water. 



TRUE PLACE. In Astronomy, the 

 place which a star or planet appears to 

 occupy in the heavens is not called its 

 true place, but that which it would oc- 

 cupy if corrections were made for paral- 

 lax, refraction, &c. ; that is, if the spec- 

 tator made his observation from the cen- 

 tre of the earth, and without the light 

 passing through a refracting medium. 



TRUMPET. The speaking trumpet is 

 an instrument, best when made of a 

 parabolic form, for rendering the human 

 voice audible at a great distance. This 

 object is accomplished by the rays of 

 sound being reflected from the interior 

 of the trumpet, as the words are spoken 

 ^ at the smaller end, in such a manner that 

 they issue from the expanded mouth 

 parallel to each other, and consequently 

 agitate the air in the direction in which 

 the axis of the trumpet is held, more 

 348 



forcibly than they would had they pro- 

 ceeded immediately from the mouth of 

 the speaker. The efficiency of this in- 

 strument increases with its length : a 

 strong man's voice, sent through a trum- 

 pet from 18 to 24 feet in length, may be 

 heard at a distance of 3 miles. 



The hearing trumpet inverts the opera- 

 tion above described, the rays of sound 

 being received at the large opening, and 

 reflected so as to become united at the 

 small aperture which is inserted into the 

 ear. 



TRUNK; STEM; &c. The former 

 term is applied by botanists to the main 

 stem of trees ; while the latter is gene- 

 rally used to denote the ascending axis of 

 herbaceous plants or shrubs, but not of 

 trees. The culm or straw is the stem of 

 grasses ; to these terms De Caiidolle adds 

 calamus, applying it to all fistular simple 

 stems without articulations, as those of 

 rushes. 



TRUTH. This term, in its strict logi- 

 cal sense, applies to propositions and 

 to nothing else; and consists in the con- 

 formity of the declaration made to the 

 actual state of the case ; agreeably to 

 Aldrich's definition of a "true" propo- 

 sition — vera est, quae quod res est dicit. 

 It would be an advantage, observes 

 Whately, if the word Trueness or Verity 

 could be introduced and employed in 

 this sense, since the word Truth is so 

 often used to denote the " true " pro- 

 position itself. " What I tell you is the 

 Truth ; the Truth of what I say shall be 

 proved :" the term is here used in these 

 two senses. 



1. Truth, in its etymological sense, 

 signifies that which the speaker " trows," 

 or believes to be the fact. The etymology 

 of the word aXr^Oet seems to be similar, 

 denoting non-concealment. In this sense 

 it is opposed to a lie ; and may be called 

 moral, as the other may logical, truth. 

 A witness therefore may comply -with 

 his oath to speak the truth, though it so 

 happen that he is mistaken in some par- 

 ticular of his evidence, provided he is 

 fully convinced that the thing is as he 

 states it. 



2. Truth is not unfrequently applied, 

 in loose and inaccurate language, to 

 arguments ; where the proper expression 

 would be "Correctness," ** conclusive- 

 ness," or •* validity." 



3. Truth, again, is often used in the 

 sense of Reality, r6 ov. Persons speak 

 of the truth or falsity of facts ; properly 

 speaking, they are either real or /c- 



