PHENOMENA OF HEAT AND SOUND. 77 



purities. The way in which he refers to the separation of 

 the slag shows that, as might be expected, the slag was a 

 very fusible silicate of iron and manganese, each removal 

 of slag resulting in a corresponding loss of iron. He him- 

 self says that steel was not often made because of the great 

 loss of iron, but less refining was needed when the iron used 

 was of good quality.* 



Aristotle's statements about sound are comparatively few 

 in number, and occur chiefly in his De Anima. There is 

 but little information on this subject in his De Sensu, dx., 

 where such information might be expected to be found. In 

 a small Aristotelian treatise, the De Audihilihus, are also a 

 few interesting statements on sound, but it is generally 

 admitted that this treatise was not written by Aristotle. 



His observations on sound furnish little that was 

 original. He reproduces in clearer language some facts 

 which w^ere well known before his time, e.g., that sound 

 was a motion of the air or other sounding body, that such 

 motion was transmitted in some way to the ear and caused 

 a sensation of hearing, and that an echo was due to a 

 rebounding of the air, a bending back or reflection of the 

 voice. In the production of an echo, he believed that the 

 air rebounded like a ball off a mass of air which, on account 

 of its being prevented from dispersing by reason of its filling 

 a cavity or vessel {ajyeiov), acted like a solid or resisting 

 body.t 



When a body, such as a bell, is sounded, there are, as is 

 well known, four things which contribute to the result : the 

 hammer of the bell, the bell itself, the air acting as a medium 

 of transmission, and the ear. Aristotle, however, held that 

 an important condition was that the air should withstand 

 the blows causing its motion and should not yield laterally 

 or disperse. If the air were struck forcibly and suddenly, 

 it would be unable to yield, but if the blow were weak and 

 slow in its action, the air would have time to escape or 

 disperse, and no sound would be produced. It was partly 

 for these reasons that he seems to have believed that wool 

 and other light substances, enclosing many air spaces, were 

 not sounding bodies, while bronze articles and other hard 

 bodies, which were polished and had no crevices or recesses 

 into which air could escape, were sounding bodies. I 



* Meteorol. iv. c. 6, s. 10. t De Anima, ii. c. 8, 4196. 



I Ibid. ii. c. 8, 4196. 



