to the Length of a Cylindrical Resonant Tube. 341 



Let L = wave length ; 



lx — length from open end to first node ; 

 Z 2 = „ „ „ second node; 



x = correction for open end. 



Then L=2(l 2 -h), and ^==^-Z 1 = Z AzA_/ 1 . 



The lengths as tabulated, however, require further slight 

 corrections to obtain the true values of l x and l 2 . The dis- 

 turbing influences are : — 



1. The slight veiling of the open end caused by the position 

 of the fork (equivalent in effect to a certain increase in the 

 length of the tube). 



2. The slight variations in the pitch of the forks, due to 

 changes of temperature. 



3. Capillary attraction. 



4. Humidity. 



I found by experiment with two organ-pipes set slightly 

 out of unison, and with plain open cylindrical tubes sounded 

 by blasts across their ends, that a fork held over one of two 

 such pipes caused an easily recognized difference in the num- 

 ber of beats ; for the forks and tube I used, the value of this 

 correction is about '0071 inch. 



For the second correction I take the variation in the pitch of 

 the forks as being equal to '00005 per vibration per degree Fahr. 



The third possible disturbing influence I found was not mea- 

 surable in a tube of the diameter used. 



The observations being taken on different days, the varying 

 humidity of the air must be taken into account : I regret that I 

 had no means of doing this at the time ; but I have availed 

 myself of the observations taken at the Royal Botanic Gardens 

 (about a mile distant from the place where 1 worked) to form 

 an estimate of the correction due to aqueous vapour. 



The dates of the observations, with the values of these differ- 

 ent corrections to reduce the results to a standard for dry air at 

 60° Fahr. are here given : — 



Date, 



1878. 



Pitch. 



Average 

 tempe- 

 rature. 



Tension 



of 

 vapour. 



Corrections. 



Sum of 

 correc- 

 tions. 



1. 



2. 



4. 











+ 









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