384 Dr. J. Burdon-Sanderson. On a New Rheotome. [May 13, 



fessor Bernstein, and described by him in his work " On the Excitation 

 Process in the Nervous and Muscular Systems," published in 1871.* 

 The other is called by its contriver, Professor Hermann, the Pall 

 Rheotome, and is described in a paper published in " Pfliiger's Archiv " 

 in 1877. I have given a short account of it, which will be found in 

 the "Journal of Physiology" (vol. i, p. 196). 



In each of these instruments, as also in the instrument now to be 

 described, two independent circuits, one of which may be called the 

 exciting circuit, the other the galvanoscopic, are successively closed 

 and immediately afterwards opened by a mechanism of such a nature 

 that the time-interval between the two closures and (as regards . the 

 galvanoscopic circuit) the duration of the period of closure may be 

 varied according to the purpose of the observation, and accurately 

 measured. In the fail rheotome each of the times required is deter- 

 mined by the measurement of the distance which a falling weight 

 passes through in the interval between the first and second event, as, 

 e.g., between the closure of the exciting and galvanoscopic circuits and 

 between the closure and opening of the latter. In Bernstein's rheotome 

 time is measured in terms of the rotation-time of a wheel, which is 

 driven by an electro-magnetic motor. 



Without making any comparison between the instrument now to be 

 described and its predecessors, or venturing to claim for it any supe- 

 riority, I think I am justified in bringing it under the notice of the 

 Royal Society, on the ground that in very numerous experiments it 

 has been found well adapted for its purpose, and that the value of the 

 results obtained by means of it could not be so well estimated by the 

 reader without a knowledge of the construction and mode of action of 

 the instrument used. 



Description of the Instrument. 



From a circular iron plate, supported on levelling screws, spring two- 

 strong brass pillars, each 6 centims. in height, on the summits of which 

 rests a horizontal bar. In the middle of the bar is a screw, which ends 

 below in a steel point. A similar steel point rises from the centre of 

 the iron plate. On these centres works a vertical axis about 5 centims. 

 in length. The steel point on which the lower end of the axis works 

 is surrounded by a circular plate of vulcanite about '5 centim. thick. 

 In this plate are cut eight pools, of which the forms are shown in the 

 diagram (fig. 1). They are intended to contain mercury and are tra- 

 versed by platinum wires, of which the arrangement is such that the 

 pools, a, a, a, a, and h, b, b, b, are severally connected with each other .- 

 The two rings of wire are insulated and are connected the one with 

 the binding-screw, G, the other to the bin ding- screw, Gr'. 



* " Untersuchnngen iiber den Erregungsvorgang ini Nerven- tujd Muskelsysteme," 

 Ton J. Bernstein. Heidelberg, 1871. 



