6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87 



readily done with the periodometer. The original data are set up as 

 usual on the right-hand drum. They are then all consecutively trans- 

 ferred to the left-hand drum on a scale of |, |, or accordant to any 

 preferred smoothing grouping of five or less. The left-hand drum is 

 then set back by the interval of one groove, and the transfer of all the 

 data is made a second time. This process is repeated five times, four 

 times, or to correspond with whatever consecutive grouping is chosen. 

 The left-hand drum will then have set up upon it a curve on the same 

 scale as the original curve, but smoothed by consecutive means. This 

 curve may be read ofT and recorded or it may be transferred back to 

 the right-hand drum as follows : Set the right-hand check screw- 

 clamp corresponding to zero of the scale, a, and all the right-hand 

 sliders at zero. Disconnect the gear train, g, h, and set the left-hand 

 pawl as described above for eliminating evaluated periodicities. Turn 

 the knurled wheel, h, towards the left till the pawl touches a slider, 

 clamp the right-hand clamp, ;', and turn back to zero of scale, a. 

 Repeat for all the data of the smoothed curve, and the right-hand 

 drum will then have upon it the smoothed curve set up ready for 

 periodicity determinations. 



As yet the periodometer has not been extensively used. It may be 

 that after longer experience with it additional automatic features may 

 be introduced which will promote speed of operation. In its present 

 form it works well. 



