664 



The Earl of Berkeley on a 



the free period. The more abrupt descent on this side of 

 the figure, of the curve for which v has the smaller value, 













20 











._ — 























• 







-— 



"' 

















T 

 78 











1 













,<& 



W 4 



























yy 



















X 



„, , 



,r 



1/1 



., 



,-, 









-, 



., , 



„ 



, c 







shows how the discontinuity which occurs in the case of no 

 friction is approached as the friction diminishes. 



It is to be noted that the maximum value of the expres- 

 sion (46) does not occur when the forced period exactly 

 coincides with the free period, but for a slightly smaller 

 value, the difference between the two values diminishing as 

 the friction is diminished. 



LXIV. Note on a Ruler for Drawing Curves. 

 By The Earl of Berkeley, F.R.S* 



IT is well known that by bending a steel ruler so as to 

 cover five experimental points, a fair approximation 

 to the true curve may be obtained, thereby affording a ready 

 means of interpolation. Should high accuracy be required, 

 it is often best to plot the known points on an extended 

 scale, the steel ruler then becomes extremely difficult to mani- 

 pulate: to obviate this, some two or three years ago I 

 devised the ruler here described. Fig. 1 gives a plan of the 

 apparatus as set up to draw a curve through the rive 

 points marked with a cross— the dimensions of the parts 

 are to the scale given on the plan, but it may be men- 

 tioned that for the highest accuracy a curve on a larger 

 scale is advisable. 



A and B are two metal T squares cut out of sheet 

 " duralumin." The two claws C and D (shown in plan and 



* Communicated by the Author. 



