for determining the Length of the simple Pendulum. 103 



fastened and riveted together; the upper part, on which the divi- 

 sions are cut, (equal to ^ of the thickness) being oi plate brass ; 

 and the under side (equal to the other f ) being of cast brass. 

 Whether it is owing to this circumstance, or to any slight injury 

 it may have received either in its packing (which is new certainly 

 not in the best order), or from some other cause, it might be dit- 

 ficult to decide at the present day; but it has a very small curva- 

 ture upwards at the ends, of sufficient magnitude, however, to en- 

 able a common playing card to be passed with ease 2 or 3 inches 

 underneath the zero end, when lying on a straight and plane 

 plank : at the other end, a piece of thin paper might be passed, 

 about the same distance. That part of the scale, which may be 

 called the standard yard, and which (as above stated) extends 

 from 10 inches to 46 inches, does not appear to be affected by 

 this distortion ; and consequently seems to be the most pro- 

 per portion of the scale to be considered as \\\e. unit of measure. 



In Captain Kater's "Account of the comparison of various 

 British standards of linear measure," inserted in thePhil.Trans. 

 for 1821, he has given the result of a comparison of 36 inches 

 on four several standards, with the same distances on Sir 

 George Shuckburgh's scale : but he has not stated ivhat part 

 of Sir George Shuckburgh's scale was selected. In his ac- 

 count, however, of the adjustment of the standard yards (Phil. 

 Trans. 1826, page 44), he states, that the distance diere used 

 was taken from zero to 36 inches : leaving it therefore to be 

 inferred that the same distance was used on the former occa- 

 sion. But, would it not have been more satisfactory to have 

 used that very distance which Sir George Shuckburgh him- 

 self adopted in his comparisons: viz. from 10 to 46 inches? or 

 (which would perhaps have been more correct,'though far more 

 troublesome) to have taken a mean of all the 240 distances 

 of 36 inches each, that might have been measured on the scale; 

 advancing by successive tenths from zero to 24 inches? 



There is also another circumstance connected with these 

 measurements, which ought to be borne in mind. Captain 

 Kater states (Phil. Trans. 1821, page 78) that his microscopes 

 were attached to a stout mahogany bar, 36 inches long, and 

 that this bar was laid upon the scale : which he considered an 

 important advantage, inasmuch as the microscopes, being once 

 adjusted to distinct vision, would not require re-adjusting when 

 placed upon another scale. But he seems to have overlooked 

 the circumstance that the bent end of Sir George Shuckburgh's 

 scale would not present the same reading when a heavy weight 

 was placed upon it: neither do I think it adviseable at any 

 time to resort to such a method. These arc points which 

 ought to be taken into consideration at any future time, if the 



))eudulum 



