80 PROCEEDINGS OF THE AMERICAN ACADEMY. 



graphic records were obtained with the coil mentioned above when it 

 was suspended by a certain short piece of wire which gave the system 

 a period of about 2.60 seconds. The next table shows (1) the values 

 of x, (2) the corresponding values of a determined by a series of 

 measurements of the diagrams from amplitudes not greater than 4°, 

 (3) the values which the damping coefficient (a') would have if 

 the air damping were absent, as calculated by aid of Table IV, and 

 finally the reciprocal (?/) of a'. Since a' should theoretically be of 

 the form 



K^7' (29) 



if the observed values of x and y be plotted, the locus should be a 

 straight line the intercept of which on the axis of abscissas is the value 



of g'. 



TABLE VII. 



x. a. a.'' y. 



As a matter of fact, the points indicated by this table lie almost exactly 

 on a line which cuts the x axis at a point the abscissa of which is a 

 little less than forty. The apparent resistance of the galvanometer 

 is, therefore, a trifle less than 40 ohms, while its real resistance with 

 this wire is less than 20 ohms. 



The Motion of a Suspended System which carries a rela- 

 tively Large Damping Vane under Righting Couples of 

 Different Strengths. 



In order to study the effects of different restoring moments upon a 

 swinging system furnished with a given damping vane, I used the appa- 

 ratus represented in Figure 3 (Plate 2). G is a uniformly wound sole- 

 noid the horizontal axis of which lies in the meridian at a place where 

 H is known. From a fine fibre in a narrow chimney inserted in the top 

 of the solenoid at the centre hangs a small bar magnet (Q) fastened 

 to a stiff mica vane in the manner shown at N. The axis of the magnet 

 is coincident with the axis of the solenoid. A small mirror on the 

 vertical wire which carries the vane and magnet lies in a vertical plane 

 which makes an angle of 45° with the vertical plane through the axis 



