4 MOVEMENT 



from the more simple to the more complicated cases. 

 We shall first show how the method can be applied to 

 register the successive phases of rest and motion, as 

 executed by a man's foot in walking, and then the 

 movements of the four feet of a horse as they occur in 

 its various paces, and, lastly, the automatic method of 

 registering the fingering of a pianist on the keys of 

 his instrument. This last problem must be regarded 

 as one of the most difficult to solve. 



Rudiments of Chronography. — Let us suppose that a 

 strip of paper is made to travel by clockwork at a 

 uniform rate, and that a pen fixed above the paper 

 marks, as it alternately rises and falls, the various 

 periods and intervals. 



As the pen comes in contact with the paper it leaves 

 its record in the form of " dashes," of various lengths, 

 and at various intervals ; and by this means the 

 sequence and duration are registered. If the " dashes " 

 are equidistant, it means that the periods of contact 

 follow one another at equal intervals of time. Finally, 

 if it is necessary to obtain an accurate measurement of 

 the duration of contact, and of the intervals between, 

 the exact rate at which the strip of paper is being 

 carried must be known. A control record of the 

 rate may be obtained by allowing the oscillation of a 

 pendulum to mark the seconds on the paper, or, if the 

 movement be very rapid, by allowing the vibrations of 

 a tuning-fork, of which the rate of vibration is known, 

 to trace themselves upon the paper.* 



Transmission of the Movement to the Recording Needle 

 which registers the Duration, — It hardly ever happens 

 that the phenomena, of which one wishes to record 

 the sequence and duration, are capable of acting 

 directly on the recording needle. More often such 



* For the jieneral principles of chronography, its technique and 

 applications, see "The Graphic Method," pages 133, 142, 456. 



