of Torpedo ocellata. 171 
Methods. In the study of a series of rhythmic movements 
three points may receive attention: these are the frequency, the 
amplitude and the form of the movements. The first may be 
‘determined with sufficient accuracy by simple observation, but for 
the study of the second and third of these factors a graphic record 
is required. For the accurate study of the form of the movements 
the recording surface must move fairly rapidly, that is to say at 
the rate of some centimetres per second. From such a record all 
‘the information required as to frequency and amplitude could be 
obtained, but only as the result of examining and measuring many 
metres of tracing, even in an experiment of moderate duration. 
As a matter of fact, in the case of respiratory movements, the 
factors of greatest interest are the frequency and amplitude of the 
movements; it is rare to find changes in form unaccompanied by 
any change either in frequency or in amplitude. For the investi- 
gation of frequency avd amplitude the most usual practice is to 
fake a tracing on a drum travelling at such a rate that the 
movements are just distinctly separated. Such a record shows at 
once the amplitude, and on counting and comparing with a time 
record it gives the frequency. Anyone who has had the task of 
counting up the number of movements per minute from such a 
tracing knows that it is exceedingly tiresome. The tracings 
moreover are very cumbersome if the experiments are prolonged, 
and mere inspection gives no indication of any but relatively large 
changes in frequency. Following on the work of Marey, Nogues* 
has elaborated an apparatus known as an odograph for the 
investigation of such series of rhythmic movements. The fre- 
quency of a rhythm studied by this apparatus is indicated by the 
inclination of a continuous line to the horizontal axis. If the 
rhythmic movements continue at a uniform rate, the line ascends 
regularly: if they accelerate, the line goes up more steeply, if 
they retard, less steeply. In the course of an experiment, it may 
pe of several hours’ duration, the frequency recorder traces a single 
oblique line. 
The method which I have used differs from that of Nogués in 
that the counting mechanism records each minute by a separate 
vertical line the number of contractions which have taken place 
in a predetermined interval of time. It is arranged as follows. 
The lever shown in Fig. 1 is used to record the amplitude of the 
movements, in the usual way. The recording lever is pivoted at 
A. At B a second lever is pivoted, the screws supporting it 
being insulated from the brass holder. This second lever consists 
of a wire bent to the form shown. On its axis there is pressed 
a piece of hair-spring which introduces sufficient resistance to 
* Trav. Inst. Marey, u. p. 31, 1910. 
