CAT A 



CATAPLASMS. 



to the ini iMiit obsmatron of their placet, with view not only to 

 amend preceding result*, and to destroy the necessary error* of one 

 observation by th* avenge of many, but also to measure more closely 

 the proper motion* of the star*. which hare, since accurate catalogue* 

 began to be formed, become visible in comparing their result*. A 

 catalogue of stars therefore ha* a value for all succeeding generations 

 in proportion to its goodness ; the comparison of two distinct cata- 

 logue* serves both to determine the precession of the equinoxes and 

 theproper motion* of the atani. 



The declination* of (tar* are observed by a method which mokes 

 their correctne** depend either upon a plumb-line, or more commonly, 



at the praaent day, u|>on .1 double observation of the star: first, 

 directly ; secondly, by mean* of an image reflected from a surface of 

 mercury. The latitude of the place, and the refractions of the atmos- 

 phere, must aUu be well known. The right ascension* of the stars, 

 relatively to each other, depend upon nothing but the correctness of 

 the instrument employed, and the uniform going of the clock. But 

 the absolute right ascensions of the stars are measured from a fictitious 

 point, the Menu r7H<No.r. The real equinox is the point at which the 

 nun crosses the equator ; but as this point mores in the heavens with 

 a motion nearly uniform, but at the same time affected with slight 

 irregularities [KqriNoxEs, KQCATIOX or], the latter are considered as 

 correction* to be applied when necessary ; and catalogues always give 

 the right ascension of the stars as measured from the point at which 

 the equinox would be, if it had it* average motion, instead of the real 

 ,. The same fiction in adopted in our measurement of time, 

 which proceeds not according to the real sun, but according to a 

 fictitious body which mores, not in the ecliptic, but in the equator ; 

 and not as the real sun moves, but with its average motion. Conse- 

 quently, the value of the absolute right ascensions of a catalogue 

 depends upon the observer's observations of the sun ; these may be 

 wrong, more or less, while his relative right ascensions may be very 

 correct ; that is, the differences of hU right ascensions may be exact, 

 while all his right ascensions may be wrong by the same quantity, 

 arising from a misplacement of the equinox. 



In the mean while, since it is certain that there are stars wh i 

 much better known than any others, it is usual to moke these, which 

 are called standard stars, the solo regulators of the clock, that is, to 

 presume that all the difference of right ascension which appears 

 between the places of those stars as deduced from the catalogue, and 

 that obtained from observation, is the fault of the going of the clock ; 

 which, corrected by these observations, is made to determine the right 

 ascension* of stars which are presumed to be not so well known. The 

 tendency of this assumption is, to moke the latter species of stars as 

 well known as the former ; bettor they cannot be by such a method. 

 Tli.- .>liervation of the sun, l.y which even the standard stars must be 

 regulated, are best mode at the solstices (from which the equinoxes 

 can be deduced), and of course occur only twice a-year. There is in the 

 Nautical Almanac for 1 862 a catalogue of standard stars, 147 in number, 

 which are reduced, and their places given for every ton days througln nit 

 the year. This last refinement, namely, the selection and constant 

 observation of a few particular stars, is due to Maskelyne (1790 and 

 1905). The standard catalogue of Maskelyne contained only 86 stars. 

 In the present day, the catalogue used for a similar purpose at the 

 Royal Observatory includes 190 stars. 



Looking further back, we find that a preceding epoch begi> 

 Bradley, whose discoveries of aU-rnitinn ami nutation <-nablcd him first 

 to reconcile the discrepancies which his predecessors bad detected, but 

 could not account for. Klamsteed (whose catalogue was published in 

 1725) was the first who habitually observed with the transit instrument 

 to the extent of forming a large catalogue. Herelius (1690) was the 

 first who determined right ascensions, not however by the transit 

 instrument, but by the old method of measuring distances of stars 

 from each other. Tycho llmhe, the restorer of astronomical measure- 

 ment, furnished the first catalogue in which any material improve- 

 ment was made upon that of Ptolemy ; for thoee of Albntegnius 

 and Ulug Beg hardly merit such a description. The catalogue of 

 Ptolemy is most probably not formed from observation, but from that 

 of Hipparchus, brought down to the time of the latter by on assumed 

 (but erroneous) value of the precession. Delambre found, by taking 

 the value 'if the prpcoution, a* given by Ptolemy himself, and reducing 

 his catalogue of utars to the time of Hipparchua, that it then presented 

 the state of the heavens more nearly than, as given, it could hare done 

 h) the time of Ptolemy. (' Astron.,' vol. i. ch. xvi.) 



CATALOG 1 T 1 



CATAU IAI.V I ic I-M|!<-K. Certain substances, when 



brought in contact nith other Rubstances, act njxm them in such 

 a manner as to induce a chemical act i "Hindu are decom- 



posed, or new one* formed, although the Hubstance by which tl,,- , 

 change* are induced is not at all affected. To thi- .-I..-, of ph. , 

 Berzelius and MiUcherlich have given the name of " catalytic action*," 

 and to the force by which they imagined them to be produced, the 

 name * catalysis,'' or " catalytic force." 



Among the examples of the operation of this force may be men 

 tioned the peculiar actions which certain metallic oxide*, mch as those 

 of manganese, copper, and iron, exert hi facilitating the decomposition 

 of chlorate of potash. When heated alone, this salt is decomposed with 

 some difficulty ; to effect iu complete decomposition, the application 



of a high temperature is ultimately required. But if a small quantity 

 of binoxido of manganese, for example, be mixed with the salt, and the 

 mixture heated, the decomposition is effected with the application of a 

 jomparatively low temperature ; the disengagement of oxygen i* regu- 

 ar, but HO rapid as frequently to produce incandescence of the mass, 

 In this cam the quantity of binoxide appears to be immaterial, it 

 undergoes no change; the decomposition is effected simply 

 presence. As additional examples may be mentioned the following 

 phenomena, which have been ascribed to the operation of this force : 

 The conversion of alcohol into ether and water by means of sulj 

 vid. in the process of etherification ; many operations of ferment 

 such as the conversion of sugar into alcohol and carbonic acid, under 

 the influence of yeast; the conversion of starch into sugar in the 

 operation of mashing wort, or in the germination of seeds, under the 

 influence of duuKut ; and the gradual conversion of amrgdaline, the 

 bitter principle of the almond, into hydrocyanic acid, hydride of ben- 

 zoyle, sugar, and formic acid, when it is dissolved in water and mixed 

 with euiuUine. 



The peculiar action which platinum exerts in effecting combination* 

 and decompositions, has also been commonly attributed to the cata- 

 lytic force. When the finely divided form of platinum, known as 

 jilatinum Marl; obtained by precipitating chloride 'of platinum by 

 means of zinc, is moistened with alcohol, and exposed to the air, the 

 alcohol rapidly becomes converted into acetic acid. When the same 

 substance i* added to a solution of peroxide of hydrogen (HO.), the 

 latter is immediately decomposed into water and free oxygen. In like 

 manner an acid solution of peroxide of barium (BaO.), is decomposed 

 into baryta (BaO), and free oxygen. Finely divided platinum has also 

 a remarkable influence in effecting the combination of bodies. Win -n 

 a small quantity of spongy platinum is introduced into a mixture of 

 hydrogen and oxygen it speedily becomes incandescent, and the gases 

 combine with a loud explosion. Similarly, sulphurous acid and oxygen 

 gases, which under ordinary circumstances do not combine, readily do 

 so when passed over gently-heated platinum black. Ammoniacal gas, 

 mixed with excess of oxygen and passed over platinum, is oxidised into 

 nitric acid and water. The reverse operation, that is, conversion of the 

 oxides of nitrogen into ammonia, may also be performed by the agency 

 of platinum. A mixture of binoxide of nitrogen and hydrogen led 

 over gently-heated platinum, yields ammonia and water. NO, + 6H = 

 NH + 2HO. 



The assumption of the "catalytic," as a special force is at least 

 doubtful. Phenomena have frequently been attributed to ito opera- 

 tion, simply because a better explanation was wanting. The progress 

 of science has shown that many reactions at first attributed to cata- 

 lysis, may be explained on known principles, and further knowledge 

 may be expected to leave none of the catalytic phenomena wit lion 

 and more satisfactory explanatii <n. The curious and interesting > 

 which platinum exerts, and which are cited by Berzelius as being 

 the most striking examples of catalytic actions, may be more easily 

 explained as being caused by the operation of the surface. According 

 . ],1 it ilium black absorbs 250 times ito volume of oxygen, 

 which must, therefore, be contained within its pores in a state of con- 

 >n greater than that of liquid water. Hence, when platinum 

 black is placed in a mixture of hydrogen and oxygen, or of binoxide of 

 nitrogen and hydrogen, or of sulphurous acid and oxygen, these gases 

 being condensed on the surface have their particles sufficiently approx- 

 imated to give play to their mutual affinities, and combination is the 

 result. The action of sheet platinum may also be similarly explained ; 

 the recent observations of lieviile have shown, that ordinary hammered 

 sheet platinum is full of minute pores. 



A curious reaction, usually held to be catalytic, is observed \vh. n 

 oxide of silver is added to peroxide of hydrogen : oxygen is liberated, 

 and metallic silver precipitated. Of this, and many other similar 



under the head OroxE. The key to their elucidation will j,, 

 ultimately be found in the views first propounded by lirodie in a 

 paper ' On the condition of elements at the moment of chemical 

 change,' read before the Royal. Society. (' Phil. Trans.' i-art ii. 7 



CATAMARAN is a name given, both in the Kant and Went Indies, 

 to some kinds of rafts which ore used in short navigations along the 

 sea-shore. The rafts which are used by the fishermen and others at 

 Madras consist of three logs of timber, each eight or ten feet long, 

 which are huhed together. With these rafts the rownrs pass through 

 the surf to fish, or to convey refreshment* to ships when no boat could 

 venture off. On the coast of South America the rafts are of con- 

 trunks of trees from 70 to 80 feet long, 



lashed together, and being from 20 to 25 feet wide : the middle trunk 

 is longer than the rest, and projects beyond them at the after 

 extremity. They carry sails on masts resembling shears ; and they are 

 steered by raising or lowering, as the occasion may require, a board 

 which enter* vertically between the timbers either at the fore or after 

 part of the raft. 



CATAPLASMS, or poultices, are substances applied externally to 

 different parts of the body, either to allay pain and repress inflamma- 

 tion, ,,r more frequently to promote inflammation or its consequences, 

 and lessen the pain attending it. For the former purpose they are 



