June 19, 1885 



♦ KNOWLEDGE 



523 



somewhat lars;er, which is lixed when the machine is in 

 ust>, Init which at other times will revolve. Encircling the 

 dial-plate »n4 resting on the lower plate is a metal ring 

 carryiiit; an arm provided with a small horizontal plunger. 

 The spring to be gauged is provided with a small collet 

 which slips over a start' (attached to which is a spring of 

 known strength) on the centre of the dial plate, and is there 

 held liy friction. The horizontal plunger above-mentioned 

 holds the stud attached to the other end of the spring 

 against the arm. Tiie ring (and with it the arm) are 



readings is taken. A table is provided as the out- 

 come of long experiment, by which it may bo found 

 at a glance what the weight of the balance must 

 be for a spring of any given strength. Thus tliat 

 spring which recorded 1,380 would bo fitted to a balance 

 weighing 911 grains. A vibrating machine is used for 

 timing the springs. A standard spring and balance are 

 susjiended from an arm, and from another arm is suspended 

 the spring to be tested. The two arms are geared together 

 and moved through a portion of a revolution and back 



Fip. 8. 



carried through a complete revolution, and an index, which 

 moves over the dial-plate with the inner end of the spring, 

 indicates the spring's strength in one direction, say in coil- 

 ing up. The ring and arm are carried back again through 

 a revolution, so that the index returns to zero, when the 

 ring is made to perform a revolution in the ojtposite direc- 

 tion to that first taken, so a'- '■.est the strength of the spring 

 in uncoiling. It is founa taat the strength in both direc- 

 tion-< i-* almost identical. Thus one we saw, being gauged, 

 carrieii the arm through 1,380 divisions each way, another 

 through 1,432 one way and 1,433 the other way. In the 

 event of the strengths varying, the mean of the two 



a'-ain, whereby the springs and balances are set vibrating. 

 It requires but little experience to determine whether or 

 not they vibrate synchronously. 



NOBERT'S RULING MACHINE. 



By John Mayall, Jun., F.R.M.S., F.Z.S. 



(Continued from p. 504.) 



171 OR the production of diffraction gratings, interference- 

 ' plates, and micrometers, where the equidistance of 

 the lines would be of extreme importance, and where the 

 breadth of space covered by the lines is so large that the 

 lever motion in arc would have produced errors in the 

 evenness of the division, Herr Nobert removed the bent 

 arm from the centre of the division-plate, and substituted 

 a vertical cylinder, on which he coiled an extremely thin, 

 fiat steel spring, having a hook at the free end. This hook 

 he attached to a stud beneath the polished steel cylinder 

 which carries the glass plate to be ruled under the diamond, 

 and which takes the place of the carrier used for the test- 

 plates. The rotation of the division-plate caused the 

 vertical cylinder in the centre to rotate, coiling the steel 

 sjiring, and thus, after the manner of a windlass, hauled 

 along" the diffraction-plate carrier at right angles to the 

 ruling motion of the diamond. 



In a former description of this part of the machine 

 (given at the Royal Microscopical Society) I stated that 

 Nobert probably used the stud and " dots " to divide his 

 diffraction gratings, &c. On further consideration, I find 

 I was in error on this point. Incredible as it may seem, I 

 am now convinced he must have used the micrometer- 



