The " Wolf-note " in Bowed Stringed Instruments. 391 



fairly indicated because of the presence of electrical circuits 

 in the neighbouring rooms of the laboratory and a changing 

 distribution of iron about the building. 



VI. Summary. 



1. A magnetometer has been designed and built, depending 

 on the property of the cathode rays being deflected by a 

 magnetic field, the deflexion being compared with that 

 produced by a known standard field. 



2. A Wehnelt cathode is used to impart a low velocity to 

 the electrons, resulting in measurable deflexions for the weak 

 magnetic fields. The deflexions are recorded on a photo- 

 graphic plate. 



3. The elimination of the earth's magnetic field for a zero 

 re i ding of the deflexion is avoided by mounting the tube so 

 as to turn about a vertical axis, and deflexions observed for 

 different orientations. 



4. The magnetometer is also a declinometer of sufficient 

 precision for setting the coil in a plane perpendicular to the 

 magnetic meridian. 



5. Account is taken of the fact that the field of the standard 

 coil is not uniform along the path of the rays, and an analytical 

 solution of the problem is found. 



6. Seven determinations of H have been made with a rela- 

 tive probable error in the fourth significant place. 



The general design and construction of the apparatus is 

 that of the senior author, who also did a part of the pre- 

 liminary work. The junior author supplied some of the 

 details of construction, deduced the formula, and made the 

 final observations and the necessary calculations. 



Laboratory of Physics, 

 University of Illinois, 

 June 9, 1916. 



XLIII. On the " Wolf-note " in Bowed Stringed Instruments, 

 By C. Y. Raman, M,A* 



[Plate IX.] 



IT has long been known that on all musical instruments 

 belonging to the violin family there is a particular note 

 which it is difficult to elicit in a satisfactory manner by 

 bowing. This is called the " wolf-note," and when it is 

 sounded the body of the instrument is set in vibration in an 



* Communicated bv the Author. 



