Intelligence and Miscellaneous Articles. 235 



Experiments on this point were made in the open air, the larger 

 disk being used with angles of 60° and 70° (from the perpendicu- 

 lar) ; the Ut 4 and Ut 5 forks were employed. 



The regularly reflected waves could be heard at a distance of ten 

 or twenty feet from the disk, the fork being held a foot or two 

 from it ; inflected waves were easily distinguishable all around the 

 disk and even a few feet behind the fork. 



When the forks were placed in the plane of the disk the alter- 

 nations of loudness were reduced to a minimum, but, in the open 

 air and in a room, never wholly disappeared. This I suppose to be 

 owing to the fact that the source of sound is not a point but a sur- 

 face. Even under these circumstances, feeble alternations were 

 heard all around the disk, the inflected waves actually returning to 

 their source. With a plain disk alternations were not perceived. 



3rd. Qualitative comparisons between the power of different sub- 

 stances to reflect sound can easily be made. 



Eor example, a disk of card-board in which filter -paper is fastened 

 over the open sectors gives alternations, owing to the difference of 

 the reflective powers of the two substances. 



4th. If a composite sound-wave falls on the rotating disk, the shorter 

 ivaves will undergo regular reflexion more copiously than the other 

 components. 



This experiment is most easily made with a reed without its 

 pipe. TJt 3 , Ut 4 , Ut 5 reeds give alternations, but mainly iu their 

 high overtones ; the alternations consequently have a ringing me- 

 tallic sound. 



5th. The reflexion of sound from very small surfaces is easily de- 

 monstrated. 



If an Ut 3 or Ut 4 reed without its pipe be employed, alternations 

 are easily obtained by moving a visiting card properly near the 

 reed. By substituting a gas-flame for the card the reflexion from 

 the flame can be demonstrated. The gas-burner should be attached 

 to a long slender rod. 



Almost all of these experiments are so easily performed as to be 

 suitable for lecture-room purposes. — Silliman's American Journal, 

 February 1880. 



EXPERIMENTS ON THE COMPRESSION OF GASEOUS MIXTURES. 

 BY L. CAILLETET. 



When a mixture of air and carbonic acid is enclosed in the 

 apparatus which served me for the liquefaction of gases, the lique- 

 faction of the carbonic acid undergoes (as already observed by 

 Andrews and several other physicists) a retardation often very 

 great : it is even possible to compress at zero C. to more than 400 

 atmospheres 1 volume of air and 1 vol. of carbonic acid mixed, 

 without obtaining any alteration of aspect in the tube. 



By compressing in the apparatus 5 vols, of carbonic acid and 

 1 vol. of air, the carbonic acid is readily liquefied. If then the 

 pressure be carried to 150 or 200 atmospheres, the meniscus of 

 the liquefied acid, which till then was concave and of perfect sharp- 



