86 C. Ba/rus and M. Barus — Plane Grating Similar to 



swivelled at a and b, 169'4 centimeters apart, and capable of 

 sliding right and Left and to and fro, normally to each other. 



The swivelling joint, which functioned excellently, is made 

 very simply of j-inch gas pipe T's and nipples, as shown in 



Fig. 1. 



Fig. 1. Plan of apparatus. AA, BB, slides ; CD, carriages ; 

 R, connecting rod. 



fig. 2. The lower nipple JV is screwed tight into the T, 

 but all but tight into the carriage D, so that the rod ab turns 

 in the screw j?, kept oiled. Similarly the nipple N" is either 

 screwed tight into the T (in one method, revoluble grating), 



