753 



ECLECTICS. 



ECLIPSE. 



761 



echoed by neighbouring clouds, or awfully prolonged by repeated re- 

 flections from an amphitheatre of mountains. 



A similar effect of rapidly repeated echoes may be perceived in the 

 prolonged tread and ringing sounds which we hear when walking in 

 stillness through long galleries, cloisters, and other narrow passages 

 with parallel sides, particularly when the ah- is confined ; but hangings 

 and carpetings, yielding to the impulse of the sonorous waves, or 

 stifling them by a multitude of interior reflections, together with 

 open windows or much furniture, diminish these effects to a great 

 extent. 



The distribution of sound hi public edifices, so that the echoes may 

 be most advantageously brought to strengthen the original sound, is a 

 subject practically deserving of much attention. For some sensible 

 observations on the errors of architects in this respect, we must refer 

 to Sir J. Herschel's treatise on ' Sound." Certainly the unlucky error 

 of placing the confessional in the cathedral of Girgenti in a focus con- 

 jugate to another, which happened to be an unenclosed part of the 

 church, by which Echo was instrumental in informing a husband of 

 the infidelity of his spouse ; and the parabolic reflector of a late inge- 

 nious clergyman at Cambridge, which had the effect of completely 

 stunning him, however impartially his voice was distributed to his 

 congregation, are not inconveniences of such common occurrence as 

 those contrivances by which a part of an audience hi a church or 

 theatre possesses a monopoly, while the remainder witness the cere- 

 mony or performance in dumb show. 



A ludicrous anecdote, mentioned by Lord Bacon, of a Frenchman 

 calling, out Satan, and being answered Va-fen, led him to assert that 

 the letter S was not echoed, and this assertion has been copied by 

 several authors. The fact is, that S being hi a great measure a 

 breathing, the distance necessary for the production of a distinct echo 

 i too great to render it audible, owing to its small intensity ; but 

 when its echo is taken at a small distance, the effect is to increase 

 the sound, and this disagreeable prolongation is very perceptible hi 

 churches whenever persons in repeating the service make use of this 

 letter. The whispering gallery of St. Paul's is another instance of this 

 error, for a low whisper uttered at one end is conveyed by successive 

 reflections along its curved roof, anfl being again concentrated at the 

 other end, may be distinctly heard, although, in such cases, it has 

 been also attributed, not to reflection, but to what Mr. Scott Russell 

 terms lateral accumulation, of the sonorous wave. 



When the reflecting surfaces, instead of plane, are curved, as in 

 caverns, grottoes, rocks, or ruined buildings, the reflected sound will 

 be most intense at the foci, or the points which would be most enlight- 

 ened by reflection if a luminous body were substituted in the place of 

 the original source of sound. 



Whatever may be the figure of the echoing surface, the total path 

 traversed by a wave in a given time before and after reflection taken 

 together is constant (and, when the time varies, is proportional to it) ; 

 therefore a small portion of a plane section of the echoing surface is 

 common also to an ellipse having one focus at the origin of sound, the 

 other in the returning wave, and the axis major equal to the space 

 traversed by sound in a given time. Hence, flrl, the plane sections of 

 the returning wave are the loci of the second foci of a series of ellipses, 

 having a common focus and equal axes major, all touching the section 

 of the echoing surface ; and, Kcondly, the figure of an obstacle neces- 

 sary to produce a given wave will be found by taking the curve which 

 touches a series of ellipses having their second foci in this wave surface 

 and their first focus and axis major as before : this should, however, 

 strictly speaking, be confined to surfaces of revolution. 



Lastly, M. Colladon has found from his experiments, that if sonorous 

 undulations excited within a fluid impinge very obliquely on its 

 surface, they do not emerge, but are internally reflected, as in the case 

 of light, forming thus an echo within the fluid. 



ECLECTICS. The name given to those philosophers who, without 

 adopting any particular system, or dogmatising for themselves, pro- 

 fessed to select (iK\iytH>) from other philosophical systems whatever 

 they conceived most conformable to truth, and fitted those detached 

 parts together so aa to form a new whole. The notion of such a union 

 of jarring systems seems first to have originated with the Neoplatonists, 

 who endeavoured to settle the dispute between themselves and the 

 Peripatetics, by the adoption of such parts of the doctrine of Aristotle 

 as could be made to tally with their modification of the academic 

 philosophy. This union of the Aristotelian and Platonic philosophies 

 was attempted first by Potamo of Alexandria, whose principles were 

 taken up and maintained by Ammonius Saccas. It may be doubted, 

 however, if the title of Eclectics can be properly given to Potamo or 

 Ammonius, the former of whom was hi fact merely a Neoplatonist, 

 and the latter rather jumbled together the different systems of Greek 

 philosophy (with the exception of that of Epicurus), than selected the 

 consistent parts of all of them. The most eminent of the followers of 

 Ammonius were Plotinus, Porphyry, Jamblichus, Proclus, and Clemens 

 Alexandrinus ; and the ancient Eclecticism became at last little more 

 than an attempt to reconcile Platonisni with Christianity. The 

 modern and more genuine school of Eclecticism sprung up in the 17th 

 century, when Bacon and Descartes flourished. These philosophers, 

 refusing to acknowledge themselves members of any particular sect, or 

 to adopt any principle on the mere authority of their predecessors, 

 formed systems for themselves which admitted the doctrines of any 



ARTS AND BCI. WV. VOL. III. 



other sect without distinction, whenever those doctrines were not at 

 variance with what their own investigation had taught them of the 

 nature of things. But modern philosophers have since then formed 

 themselves into new sects, and a new Eclecticism has consequently 

 arisen in our own days, of which the originator was Hegel, and the 

 most eminent supporter Victor Cousin ; this newest Eclecticism re- 

 sembles that of the Alexandrian Platonists in being rather a union of 

 systems than a selection from them. 



ECLIPSE (ecleipsis, eitXenJ/is), an astronomical phenomenon, being 

 the disappearance of a heavenly body. This may happen in two dis- 

 tinct ways ; either the disappearing body may be lost on account of 

 another body coming between it and its source of light, and thus 

 intercepting the light ; or the disappearance of a body may be caused 

 by another body coming between it and the spectator. These two sets 

 of circumstances, though ending in the same species of phenomenon, 

 are yet of a character so different that it will be advisable to consider 

 the two in separate articles. We shall therefore here content ourselves 

 with an enumeration of the various kinds of eclipses; leaving further 

 detail, when necessary, to the articles which will be referred to. 



Let us suppose a spherical body A u, which is lurninotis, and another, 

 c D, the smaller of the two, which is not luminous. Let us consider 

 first the circular sections of these bodies made by the plane of the 

 paper, and let common tangents be drawn to these sections, four in 

 number, namely, A x, B Y, A M, and B N. If the bodies be very distant 

 from each other, in comparison with their bulk, then it will be suffi- 

 cient for practical purposes to consider these common tangents as 

 intersecting at A and B and c and D, the opposite extremities of two 

 parallel diameters. If the whole figure then revolve round the line 

 joining the centre of the two circles, the spherical bodies will be re- 

 produced, together with the conical envelopes by which it may be 

 seen on what the phases of an eclipse depend. 



The whole space generated by the revolution of Y c D x is, in whole 

 or in part, deprived of the light from A B. Within the space c D z 

 (or the cone generated by its revolution), the loss of light is' total : 

 a spectator situated within that cone sees no part of A B, and a planet 

 which receives its light from A B cannot, when in that cone, be visible 

 in any part of space. This is even true at the point z ; but any- 

 where within the cone N z M, more or less of. the border of A B is visible, 

 and c D hides a portion of the middle of A B. If c D be small in com- 

 parison with A B, then the effect of c D to a spectator situated far off 

 hi N z M is only the appearance of a small dark spot upon the face 

 of AB. 



Within the spaces Y c z N and M z D x, a part only of the face of A B 

 is hidden from a spectator there situated, and part only of the light of 

 A B is lost. On the lines c Y or D x the spectator imagines the two 

 bodies A B and c D to be in contact. 



The eclipses in which the disappearance takes place by the removal 

 of the light from the body are 



1. The eclipse of the moon. [LUNAR ECLIPSE.] 



2. The disappearance of a portion of Jupiter's surface, occasioned by 

 one of its satellites passing between it and the sun. This is usually 

 called the transit of the satellite's shadow over the disc of Jupiter. 

 [JuriTKR.] 



3. The eclipses of Jupiter's satellites. [JupiTEK.] 



The eclipses in which the disappearance arises from the absolute 

 interposition of another planet are 



1. The eclipse of the sun [SoLAB ECLIPSE], meaning the eclipse of 

 the sun by the moon. 



2. The eclipse of the sun (that is, of a very small portion of the sun) 

 by Mercury or by Venus, commonly called the transit of Mercury 

 or Venus over the sun's disc. [MERCURY, TRANSIT OF; VENUS, 

 TRANSIT OF.] 



3. The occultation of a fixed star by the moon. [MooN.] 



4. The eclipse of a portion of Jupiter by one of its own satellites, or 

 transit of a satellite over the disc. [JUPITER.] 



5. The eclipse of a satellite of Jupiter by JupiterJtself, or occultation 

 of a satellite by the planet. [JUPITER.] 



We have here mentioned such eclipses as are not unfrequent : the 

 only additional phenomenon which we are aware of is the eclipse of a 

 portion of the ring of Saturn by a satellite, or passage of a satellite 

 over the ring, seen by Sir W. Herschel. The satellites of Saturn must 

 suffer eclipses of the first kind by entering the shadows either of the 

 planet or the ring, and of the second kind both from the planet and 

 the ring ; bufc- these satellites are only seen with very good telescopes 

 and under very favourable circumstances, so that their eclipses excite 

 little public curiosity. For an account of the physical phenomena 



So 



