12 



AET. 10. — T, TEEADA. 



into or removed from the lower part of the pipe, in order to 

 adjust the length of the air column inside the pipe at will. A 

 thin plate of zinc, 0.4 mm. thick, was fastened on the open 



end to cover it partially, leaving 

 a segmentary aperture between its 

 straisiht edo;e and the edsje of the 

 pipe. In order to secure a close 

 contact between the plate and the 

 polished end of the pipe, a small 

 (juantity of tallow was applied to 

 the ]ilaee of contact. The area of 

 the segmentary aperture was calcu- 

 lated from the length of the arrow. In the annexed figure, tlie 

 area of the segment A B ( - is given by 



where 



= 



r~i> 



r being the radius and j} = CX. A strip of glass graduates 

 throughout its entire length was a})])lied to aperture so that its 

 end came into contact with the edge of the zinc plate and the 

 value of 2^ was estimated to the tenth of a milimeter. 



The tuning Ibrks used consisted of a set of lo forks giving 

 a tempered chromatic scale within the range of Cj to c... The 

 number of vibrations of these forks had been previously deter- 

 mined approximately in comparison with a set of standard forks 

 made by Koenig. For lower notes, Koenig's forks giving >^ol , 

 Mi-j, and Ut.., were employed. 



First the air column within the pi})e was adjusted to a 

 desired length /. The diiïerent forks were successively brought 



I 



