78 



Intelligence and Miscellaneous Articles, 



mobility to the solution. — Bibliotheque Universelle, Archives des 

 Sciences Phys. et Nat. No. 197, pp. 75, 76. 



A NOTE ON MELBE'S EXPERIMENT. BY W. LOWERY. 



In performing Melde's experiment upon the vibrations of 

 strings, it is desirable to change the tension of the vibrating cord 

 in a continuous manner. The ordinary method of attaching 

 weights to the cord does not admit of this with precision ; and with 

 small weights the movement of the weight itself, on account of the 

 rapid vibration of the string, prevents the formation of the ventral 

 segments with regularity. I have adopted the following method : — 

 A glass tube graduated into millimetres is weighted so as to float 

 in a vertical position : this is attached to the silk cord which 

 hangs from the prong of the tuning-fork, and is placed in a glass 

 vessel filled with water. This latter vessel is provided with a 

 siphon, by means of which the water can be drawn off at pleasure. 

 It will be readily seen that, by drawing off the water from the 

 larger vessel, the displacement produced by the graduated glass 

 tube is diminished, and the tension of the string thereby is increased. 

 By diminishing or increasing the amount of water in the larger 

 vessel the tension can be diminished or increased to the desired 

 extent. 



In order to make quantitative experiments, the tube is in the first 

 place connected with the arm of a delicate hydrostatic balance. 

 The balance is adjusted when the level of the water in which the 

 tube floats is at the zero of the millimetre scale. In order to 

 avoid errors in reading, it is best to use a cathetometer. The 

 weights which are necessary to keep the index of the balance at 

 zero, when the level of the water in the outer vessel falls through 

 the millimetre divisions on the graduated tube, are noted. The 

 upward pressure of the water, and consequently the tension upon 

 the suspending cord, are then given in grams. 



In order to show the regularity of the method, the following 

 results of one experiment are given. In the experiments, a glass 

 tube which, immersed at 110 millims. on the scale, weighed two 

 grams gave, when the level of the water in the outer vessel was 

 lowered, the following : — 



Immersed at 110 milHms. 



Wei 



ght 



= 2 grams 



102 „ 







2*5 „ 





, 93*5 „ 







3 „ 





, 85 „ 







3-5 „ 





76-5 „ 







4 „ 





67-5 „ 







4'5 „ 





60 „ 







5 „ 





43 „ 







5-5 „ 



In these experiments a fall "of 8*1 millims. corresponded to a 

 difference of -5 of a gram. It is evident by increasing the size of 

 the outer vessel that a large amount of water would measure a 

 slight displacement. When the cord was set in vibration, the fol- 

 lowing results were obtained : — 



