ECHO 



1914 



ECK 



to the prickly covering characteristic of many 

 members of the group. According to the mod- 

 ern classification, the echinoderms are ranked 

 between the insects (Arthropoda) and the 

 vertebrates. All make their home in the sea. 

 They are divided into starfishes, sea urchins, 

 brittle stars, sea cucumbers and sea lilies. 

 Their typical structure is that of a central 

 "disk, from which five arms radiate, much as 

 the spokes of a wheel branch from the hub. 

 In some species the arms divide again and 

 again. The mouth is located on the underside 

 of the central disk. 



Embedded in the body wall of nearly all 

 echinoderms is a skeleton made up of minute 

 plates consisting of lime and carbonic acid. 

 These plates often bear spines, which are ad- 

 mirable weapons of defense and also serve to 

 protect the internal organs. The organs of 

 digestion and reproduction are contained in a 

 body cavity enclosed by the body wall. Sea- 

 weed, clams, oysters, barnacles and other ma- 

 rine animals are consumed by some species, 

 and the sea cucumbers take into the body 

 large quantities of sand. There are about 

 3,000 living species, found in all the seas of 

 the globe, but they are most abundant in trop- 

 ical waters. 



Related Subjects. The reader is referred to 

 the following articles in these volumes : 

 Arthropoda Sea Urchin 



Crinoidea Starfish 



Sea Cucumbers Vertebrates 



ECHO, ek' oh, a reproduction of sound 

 caused by sound waves striking an obstacle 

 and being thrown back towards their starting 

 point. How sound originates is explained un- 

 der the title SOUND, in these volumes. Whether 

 or not the word echo was applied because of 

 the old Greek myth described below, people 

 will nevertheless always associate it with that 

 pleasing, sentimental tale. 



An echo may be reflected from a building, a 

 hill or other obstacle, either directly back 

 towards the point at which it originated, or 

 at such an angle that the sound cannot be 

 heard at the point of origin. Sound travels at 

 the rate of 1,080 feet per second when the 

 temperature is at the freezing point. The echo 

 travels at the same speed as the original sound, 

 so that anyone standing 540 feet from the 

 reflecting obstacle would hear the echo in one 

 second, if it. were sent straight back to him. 

 The velocity of sound increases at the rate of 

 two feet per second for every rise of one degree 

 in temperature; in the average temperatures of 



North America it travels about 1,125 feet per 

 second. 



At Woodstock, England, there is a remark- 

 able echo which repeats fourteen syllables, 

 but in most cases the echo can only make 

 audible such sounds as can be heard in one 

 second. A single sound such as a shout may 

 be thrown back distinctly by many cliffs, but 

 a sentence is usually a confusion of sounds, 

 and only the last syllable is audible. An echo 

 is often helpful to mariners in foggy weather 

 by enabling them to calculate the distance to 

 cliffs from which the sound is reflected. The 

 time between production of the sound and 

 hearing of the echo is noted, and the distance 

 is easily ascertained. 



In Greek Mythology. Echo was a beautiful 

 nymph, an attendant of Diana, the huntress, 

 and noted for her conversational powers. On 

 one occasion when the jealous Juno was seek- 

 ing her husband Jupiter, believing him to be 

 with the nymphs, Echo detained her in con- 

 versation until Jupiter escaped. The goddess 

 punished her by condemning her never to 

 speak first, and always to repeat the last word 

 she heard from others. A more poetic version 

 is that Echo fell in love with Narcissus, a 

 beautiful youth insensible to love, and because 

 he did not return her affection she pined away 

 until nothing was left but her voice, which 

 may still be heard in the mountains, speaking 

 only when spoken to and replying only in the 

 exact words of the speaker. Many poets have 

 found inspiration in this legend, among them 

 Shelley in his poem Adonais: 

 Lost Echo sits amid the voiceless mountains, 



And feeds her grief. 



ECK, JOHANN MAIER VON (1486-1543), a 

 German debater and writer, and powerful op- 

 ponent of Martin Luther, was born in Suabia. 

 He entered the University of Heidelberg at 

 the age of eleven and obtained a degree at 

 Tubingen when he was fourteen. In 1510 he 

 became professor of theology at Ingolstadt, 

 and in 1518 wrote and privately circulated a 

 pamphlet against Luther's thesis on the mass. 

 Carlstadt, who was a most extreme reformer, 

 and Luther wrote replies to this work, and 

 Eck finally challenged Luther to debate with 

 him at Leipzig on the Papal supremacy. This 

 meeting took place in June, 1519, and after a 

 discussion of three weeks, he forced Luther 

 into an admission that, under certain circum- 

 stances, it might be right to disobey the Pope 

 and the great Council of Constance. Eck left 

 Leipzig the victor in the encounter but still was 



