PARAFFIN. 



I'AKALLAX. 



0u ' > v *~f 



Ba...|. Hunby* 1Mb Sermon :- 

 wparatoly proved, each by iu 

 dnying either, that the huuu 



to a propoMlion which i* oppoeed to the general belief, 

 t appear* at ftrat aight to contradict aome previously aecer- 

 tamed froth The nature of a paradox and the dbtmction between it 

 .nd a eoatradirtion b dearly explained in the following Mntenee from 

 : " When two diatinot proposition* are 

 proper evidence, it b not a reaaon for 



denying "either, that the "human mind, upon the firat hanty view, 

 ' Me > repugnance, and may perhap* find a difficulty in connecting 

 even after the dutinct proof of each i* clearly perceived and 

 rtood. There U a wide difference between paradox and a con- 

 tradiction. Both, indeed, eonaict of two dutinct propoaitioiu, and so 

 far only are they alike ; for of the two parU of a contradiction, the one 

 or the other mu*t neceeearily be fal*e : of a paradox, both are often 

 troe, and yet, when proved to be true, may continue paradoxical. 

 Thi* b the neceecary ooneequenoe of our partial view of things. An 

 intellect to which nothing should be paradoxical would be infinite. 

 In all UMM owe* there i* generally in the nature of things a 

 limit to each of the two contrasted propoaitions, beyond which neither 

 can be extended without implying the falsehood of the other, and 

 j the paradox into a contradiction ; and the whole difficulty of 



living the connection and agreement between such propositions 



arieee from thi* circumstance, that by aome inattention of the mind 

 the*e limit* are overlooked." 



Thb word wa* also used by the Greeks for a remarkable saying. 

 Cicero, in hi* work entitled ' Pandoxa,' illustrate* six of these para- 

 doxes, borrowed from the Greek stoic*. These propositions are the 

 following : 1. The honourable is the only good. 2. Virtue is sufficient 

 for happlneei. 3. All rin* and right actions are equal 4. Every fool 

 i* mad. 5. The wiae man alone is free, and every fool is a slave. 

 6. The WIM man alone i* rich. 



PARAFFIN (C,H.,f). A white crystalline body first found by 

 Beichftitmrh in coal, wood, and animal tors. He found that the lower 

 the temperature at which the tar was produced the larger the amount 

 of pr-K" formed. It is now obtained in large quantities by distilling 

 eannel coal at the lowest temperature practicable, the rectified and 

 purified product constitutes the basis of paraJKa nil. The tar is filled 

 with crystal* of paraffin, which may be collected upon a strainer, and 

 purified by pressure and treatment with concentrated sulphuric acid 

 and caustic aoda alternately. 



Paraffin U a beautifully white translucent body, like spermaceti, and 

 when manufactured into candles gives a clear smokeless light. It 

 fu*e* at 110* Fahr., and is remarkable for its resistance to chemical 

 action ; hence its name from parum a fin it. 



PARAFFIN, is one of the numerous substances which chemical 

 discovery has added to the list of liquid fuels for lamps ; its nature 

 may in aome degree be shown by the proceedings in a chancery suit 

 which took place in 1854. In 1850, Mr. Young hod taken out a 

 patent for " the treatment of certain bituminous mineral substances, and 

 in obtaining product* therefrom." It was Paraffin oil, obtained from 

 bituminous coal. The coal was distilled at a low red heat. If a 

 higher temperature were employed, the elements would be converted 

 into gai and naphthaline ; but the lowness of the heat prevented this, 

 and brought over the product as an oil rich in paraffin ; and this oil, 

 when purified, became useful as a fuel and a lubricator. On the other 

 aide, it appeared that the Hydro Carbon Gas Company of Manchester 

 were the owner* of two patents, obtained by Mr. White, for inventions 

 relating to the gas manufacture. One was for obtaining a compound gas 

 from the vapour* of oil, fat, and tar, combined with hydrogen obtained 

 by the decomposition of water ; while the other was for using resin, 

 tar, fat, or pit coal for the some purpose, but at a white red heat. 

 The defendant* cold an oil which they called Paraffin oil, and which 

 the j.Uintiff churned as belonging to his patent. The defendant 

 pleaded that paraffin is not a new substance, it having been pro- 

 duced many years ago by Reichenbach, who showed that it can be 

 obtained from wood-tar and coal-tar. The decision was in favour 

 of the plaintiff, as having adopted a low temperature for obtaining 

 paraffin, on finding that a greater heat would result in the production 

 of napbthalin. 



PAKAFKIN OIL. fPARAFFix.] 



PARALLACT1C ANGLE. The angle which measures the parallax 

 of a eeleatial body. [ PARALLAX .] 



PAKALLACTIC INSTRUMENT, or PtoUmy', Rnlet, the name 

 given to an instrument invented by Ptolemy for determining the 

 moon* parallax, and described by him, ' Almagest,' b. v., c. 12. 



A >, B c,fg. 1, are two (tout wooden rods turning on a pin or centre 

 t>; B A = B c ; A c U a third divided rod, also turning on a pin at A, 

 and pauing through a loop or bifurcation of the rod B c at c ; p Q, a 

 plumb-line by which A B U adjusted vertically ; E F, two sights fixed 

 on c B. It i* evident, if A B be truly perpendicular, and any object be 

 Men in the direction X r, that A c will be the chord of the angle ABO, 

 that U, of the zenith distance of the object. A c may be divided as a 

 Male of equal part*, and the angle deduced from a table of chords, or 

 a* a line of chord* to radius A B, in which case the angle may be read 

 off at once.* 



e Ion* Ubertle* bare been taken with Ptolemy'* description, and aereral 

 oalHlon* made. ICe aeenu to bare ben alnfularly unlucky u an obtcirer, for 

 at M' JJ' Appar. Z*m. Dirt, b* found the mooa'a parallax = 1 7', whence the 



A figure of a similar instrument may be found in Tychu Hi .!, 

 Antroo. Instatir. Mechanica,' sheet c. We have thought Pi- 



. 1. 



llulrt worth notice chiefly as pointing out a very cheap and accurate 

 instrument for obtaining the time by the method of equal altitude:). 

 Let A B be a rod turning on pivots above and below, for instance, 

 between the sill and architrave of a window, and capable of being set 

 perpendicular by a plumb-line, supposed in the figure to hang behind 

 A B. K c, a stout edge-bar turning round a pin at o, and fixable in any 

 direction by two laths, E u, c N. On K c a telescope is lashed (one 

 sufficient for the purpose might easily be made of a tin tube and 

 spectacle-glasses), with one or more horizontal wires placed in the 

 focus. If the times of contact of the sun's limbs with the hori- 

 zontal wires be observed in the forenoon and again in the afternoon 

 (the axis A B being in both cases truly adjusted, and the instrument 

 in other respects unchanged), the data will be obtained for finding the 

 time shown by the watch when the sun is on the meridian that is, 

 apparent noon with great accuracy and very little calculation. (See 

 Schumacher's ' Hulfstafeln,' p. 49, &c. ; Bail/s 'Tables,' pp. 92, 148, 

 and many other collections.) The determination of the error of the 

 watch by equal altitudes of the same star is even more simple, as 

 there is then no motion in declination to be allowed for, and the 

 middle time by the watch of similar observations is the time when the 

 star passes the meridian, or its right ascension, which is known from 

 the ' Nautical Almanac,' or from well-known catalogues. The observer 

 must be very careful to adjust the instrument by the plumb-line to 

 the same position in both observations, and he must have a watch 

 which will keep time correctly for the interval. 



Sometimes the word jxiratlactique is used to signify the instrument 

 known to us by the name of EQUATORIAL. I^alande (' Astronomic,' 

 2278) says the proper word is parallatique, or that which follows the 

 parallel of stars ; he reserves /tarallaclique for Ptolemy't Hula. 



PARALLAX (*apd\\atts), used in astronomy generally for the 

 angular variation in the position of an object caused by the cxeentric 

 situation of the observer with respect to a certain point of reference. 

 Thus the parallax of the moon, sun, planets, comets, is the difference 

 between the position of any of those bodies as seen from the surface of 

 the earth and that iu which they would be seen if the observer were 

 placed at the earth's centre. The |>arallax of the fixed stars is the 

 difference between their places as seen from the earth and from the 



sun, which is for these observations the point of reference. All bodies 

 within the solar system are in the first instance referred to the earth's 

 centre ; while those beyond our system, as the fixed stars, are referred 



hcrironUl parallax in 1 26', and the diitoncc of moon from the earth 39-8 of 

 the earth's radii. Ho hat drawn the latter conclusion, but fortunately scemi 

 not to hare uied it in bin theory. 



