210 W. K. BRIDGMAN OX A NEW ANTI-VIBRATION TURNTRAY. 



others, and the vibrations of the one will be counteracted by the 

 other. To obtain greater stiffness, four other pairs of rings — one 

 within the other, forming a cross and expanding in opposite directions 

 — are inserted midway at the ends and sides, as at c, c. ; while to 

 prevent flexure and warping, four pieces of thin board are glued 

 across the inner sides so as to fit alternately without touching — as 

 shown in Fig. 4 — an edge view of the two when put together, 1 and 

 1 being on one board and 2 and 2 on the other. 



Although this arrangement has been found perfectly successful 

 against the upward tremor arising from street traffic and the passing 

 of vehicles, it is not proof against the swinging motion of an elastic 

 floor, without having a corresponding arrangement applied to the 

 edges in addition. To accomplish this, it only requires to have a 

 ledge attached to the two sides of the lower board, rising up to the 

 level of the upper surface, and having indentations to receive the 

 compressed rings b, b. Fig. 5, which prevent the boards touching 

 each other. In order to avoid the corner rings being too much 

 stretched when not in use, it is desirable to have the boards kept 

 together by a hook and pin at the four points, two of which are seen 

 at e, e., Fig. 84, but which must be turned quite clear of the upper 

 board when being used. By covering the lower side with thick 

 baize or cloth, it will be found to slide freely on a polished table 

 without scratching, and by supporting both light and instrument, the 

 whole may be passed from one observer to another as a "turntray," 

 without having to rise from the seat, which is a great comfort to all 

 concerned. 



Description of Plate XIX. (Upper Part). 



Fig. 1. Section of board on four springs as not checking vibration. 

 „ 2. Ditto, showing Fig. 1 inverted upon a second similar set of springs 



so that the vibrations of one are counteracted by the elasticity of 



the other. 

 „ 3. Inside arrangement of two boards separated by india-rubber rin°-s. 

 „ 4. Side view of Fig. 3, when the two boards are put together. 

 „ 5. Front view, showing the tension rings upon the corners, and the side 



springs to counteract lateral motion. 



