

NO. 4 THE PERIODOMETER — ABBOT 5 



grasps one of the sliders on the left-hand drum. The vertical pawl 

 used in pushing the sliders of the right-hand drum to their positions 

 is now pushed by the rack and knurled wheel, h, until it touches the 

 slider lying at the top of the right-hand drum. A train of gearing. 

 g, h, variable through ratios ^, ^, ?,. and ^ operates simultaneously a 

 rack carrying the knurled head and its vise-clamp, /, and thereby 

 pushes the front slider on the left-hand drum through ^ (or other 

 preferred fraction) of the travel of the pawl. 



Returning to zero of the scale, a, the two drums are then moved 

 forward one division by making a single rotation of the knurled 

 wheel, i. The above process is repeated until as many sliders are set 

 on the left-hand drum as there are data in the periodicity sought. Let 

 us assume for illustration that these data number 8. Thus the indi- 

 vidual values of this interval of 8 data are reproduced on J scale on 

 the left-hand drum. That drum is now reversed to its starting posi- 

 tion, and a new series of 8 pushes is made. As these new pushes start 

 from the positions already attained, we now have the average of the 

 first 1 6 data reproduced on f scale. Repeating the process until 40 

 data are covered, the left-hand drum then exhibits the mean value of 

 the 8-datum periodicity over an interval of 40 data. 



If the periodicity sought seems real, as revealed by the form of the 

 mean curve thus determined, it may next be read off and recorded. 

 Fresh data on the right-hand drum may then be used to give a second 

 and a third determination of the 8-datum period. If these new deter- 

 minations of it harmonize fairly with the first, then it is clear that the 

 8-datum period exists throughout the w^hole interval of the data. A 

 mean of the three determinations is taken to represent it. 



The general mean form of the 8-datum periodicity is next set up 

 on the left-hand drum and clamped. The sliders of the right-hand 

 drum are loosened. Then, employing the vise-clamp, ;, and a second 

 pawl available for the left-hand drum, all the sliders on the right-hand 

 drum are moved toward the left through distances determined by the 

 periodic setting of the sliders of the left-hand drum. This average 

 8-datum periodicity is used end to end successively so as to remove 

 completely the average 8-datum periodicity from all the original data. 

 Thus a residual curve remains, from which the average 8-datum 

 periodicity has been eliminated. 



The same procedure is repeated with any other periodicities which 

 seem to be displayed by the settings of the sliders on the right-hand 

 drum, until all promising possibilities are exhausted. 



It is frequently desirable to take consecutive means of several data 

 at a time in order to smooth a long series of observations. This is 



