274 Mr. K D. C. Hodges on a 



intensity with which a sound is perceived for the various 

 positions of the head. 



The circumstances adduced in the first three points may be 

 regarded as the advantages, those in the last three as the dis- 

 advantages entailed by relatively increasing the value of the 

 angle /3. 



12. In conclusion let us finally draw attention to the fact 

 that estimates of direction may be made in many cases in 

 which, according to the preceding theory, the faculty of so 

 doing is strictly wanting to the organs of hearing. Without 

 entering further upon the circumstances involved by this ap- 

 parent difficulty, be it simply remarked that often the most 

 inconsiderable and apparently unimportant things are accus- 

 tomed to suggest a particular position as that of the spot in 

 which the source of sound is situated, so that then this power 

 of finding the direction is falsely ascribed to the ear. 



Just in this manner, as estimations of depth or distance 

 can theoretically be made by one eye in a very defective way 

 only, and yet are again and again easily made owing to mani- 

 fold circumstances which stand in no direct connexion what- 

 ever with the faculty of adjustment of the eye, so also estima- 

 tions of direction of sounds are made by the aid of other cir- 

 cumstances without recourse to the particular faculties of the 

 ear. 



Moreover, the more excitable the imagination of man is, 

 the more easily will he see and hear things at a place where 

 really there is nothing to see and nothing to hear. 



XLIII. On a new Absolute Galvanometer. By N. D. 0. 

 Hodges, Assistant in the Physical Laboratory of Harvard 

 College, Cambridge, Mass.* 



IN the ordinary form of galvanometer the current is mea- 

 sured by the ratio of the force it exerts on the needle to 

 the directive force of the earth, the ratio being determined by 

 a measurement of the angle of deflection. 



The moment of the force with which a unit current acts on 

 the needle may be expressed in a series of the form 



Gtf 1 sin0 + G# s sin0Q' a (0) + &c. (Maxwell, § 109). 



Gi, G 2 are constants depending on the dimensions of the coil, 

 and g Y , g 2 on those of the suspended apparatus, coil or mag- 

 net, as the case may be. Q'viQ), Q r z(y) are quantities which 

 may vary with the deflections. 



Only in case all the terms after the first may be neglected 

 * Communicated by the Author. 



