324 Scientific Intelligence. 



thousand which come within the limit of experimental possibiUty 

 would give a spark about 92 inches long. Probably a million 

 would never be made but they should give a spark 9166 inches 

 or 764 feet long. — Kature., xiii, 277. e. c. p. 



10. Acoustics. Letter to the editors by Professor A. M. Maykk, 

 dated Stevens Institute of Technology, Hoboken, New Jersey, 

 March 17th, 1876. — Gentlemen: Having in hand researches whose 

 completion will occupy several months, I desire to place on reeoi J 

 my invention of the two following methods of research. The tiist 

 I for the determination of the relatice intensities of souiuJs 



m 



I pitch. The second is a method of determiu 



las after I have finished the 

 3 all my leisure. 

 , ^ ir a slip of gold or alumin- 



ium foil, is placed anywhere between the centers of origin of 

 two sounds of the same pitch. The plane of this membrane is at 

 right angles to the line connecting these sonorous centers. If 

 both sides of the membrane are simultaneously acted on by sono- 

 rous vibrations of the same phase and of equal intensity, the mem- 

 brane will remain at rest. The above condition is thus attained. 

 Attach to the center of the membrane a short delicate glass 

 thread whose end can be observed through a microscope, or, place 

 a reflecting metallic film on the central paii; of the membrane so 

 that one can observe the motion of a beam of light reflected 

 therefrom. If we place, at hazard, the membrane between the 

 sonorous centers it is probable that it will be set in vibration. 

 Now if it is moved from its position its vibrations will either in- 

 crease or decrease in amplitude. Move it in the direction thai 

 causes the amplitude of the vibrations to decrease, and until the 

 vibrations have a minimum of swing. The membrane is now ni 

 a plane where the phases of vibration are the same but of uneqnxl 

 intensity. The membrane is now moved one-half wave-leuutli 

 either from or toward one of the sonorous centers and is tlius 

 brought into another plane of minimum vibration. Thus tn-no 

 the membrane until it is brought into that plane where vibrations 

 of the membrane are either entirely destroyed or l)ave their U a>t 

 amplitude. If the membrane vibrates, then move it and the 

 source of one of the sounds so that they both approach to oi- re- 

 cede from the other sonorous center always by the same quantity. 

 This is accomplished by moving a board to which is attached the 

 membrane and one of the sources of sound. By the last adjust- 

 ment we can soon reach a plane where the membrane remains at 

 rest and where the intensities of the two sonorous vib rat ions are 

 ; appears that I have thus devised a. phonometir which is 



described in this Journal, Feb., 1873. There 2 

 he use of resonators and reflection which I canr 

 Second method. If the plane of a free membr;? 



