Nixon, H. K. (1924). A Sphygmograph with an Electric Attachment for Recording Pulse Rate at a Distance. Journal of Experimental Psychology, 7(5), 358-370.
http://dx.doi.org/10.1037/h0075547
The article describes a new sphygmograph which can be attached to the pulse in the wrist by means of a simple lever-device and a pair of weights which control the amount of pressure brought to bear upon the wrist. The apparatus is so made that it will remain properly adjusted for an indefinite length of time, and for this reason has been found useful in ordinary laboratory work. The record can be made with ink upon plain paper as well as by marking on a smoked drum. The writer appends a survey of sphygmographic devices which already have been employed, and also adds a long bibliography. From Psych Bulletin 22:12:00845. (PsycINFO Database Record (c) 2016 APA, all rights reserved)