396 



Mr. A. Mallock. Soini' Mi"-'ireg of [Mar. lit, 



Explanation of tJie Diagram*. 



Diagrams (1) to (9) are examples of the diagrams used in determin- 

 ing the ratio R/n. 



The ordinate is the scale-reading on the arm D (6g. 1). un<l the 

 abscissa the corresponding scale-reading of the images of the gU 

 scale seen in the field of the telescope. 



That the line through the ob>ervations does not in general point 

 the origin is due to the fact that the mirrors were not quite para! 

 in a vertical direction at the beginning of the experiment ; in fact, 

 according to the position in which the spring holding the mirrors 

 against the faces of the gauge was placed while they were being 

 cemented to the beam, variations of rather more than a minute of ar 

 were produced between their planes. The abscissa reading when 

 ordinate = has of course to be subtracted from n in getting 

 true ratio B/n. 



The spots indicate individual observations, and are mart 

 with arrows whose directions show whether the load was beii 

 increased or diminished. 



Diagram (5). t 



b 



W 



Diagram (6). / 



b 



W 



Diagram (7). t 



b 



W 



= 0-0473 inch -j 



= U-1190 > bismuth. 



= 0-0671 Ib. J 



= 0-0304 inch 1 



= 0-0757 > carbuncle 



= 0-0671 Ib. 



= 0-0369 inch 

 = 0-0911 

 = 0-0671 Ib. 



quartz. 



