Perhaps the most widely recognized instrument of medical examination is the binaural stethoscope with two ear tubes, patented in 1855 and used to detect cardio and respiratory abnormalities. The earlier version, the monaural stethoscope, is a simple wooden tube with a flare like a bugle at one end. Craniometers and cephalometers originated in the 1820s and 1838, respectively, to relate the shape of the human skull to mental attributes (phrenology). The sphygmograph, invented in 1860, graphs pulse rate, succeeded in 1881 by the sphygmomanometer which in turn evolved in 1886 with the now familiar inflatable arm band;. the hemoglobinometer that measures red pigment in blood; and the haemacytometer, which consists of a pair of small thermometer-like pipettes and used to examine white and red corpuscles. The tuning fork, invented in 1771, became important in physics, then in hearing diagnosis a century later. They were superceded by electronic vacuum tubes during the 1920s, then electronic devices by the end of the millennium. An Olfactory tester from the early 1800s tests smell sensation. The Tachistoscope, a mechanical device that tests visual attention and response time to a variety of stimuli was developed in the 1890s. Modern counterparts are electronic and digital. Electrical shock treatment began in the 1700s and in 1782 a medical electrical machine or induction coil was patented. A single filament, hung between the poles of a magnet were used in 1897 as electrocardiographs. The similar electroencephalograph, invented in 1902, measures electrical activity in the brain. These devices derive from the kymograph, an instrument invented by Wilhem Wundt in the 1840s. Galvanometers were used in 1844 to develop the first electromyographs to detect electrical currents related to muscle activity, and the electroretinographs that study electric potential in the retina related to reaction to light intensity emerged in 1849. The polygraph, well known today as the lie detector, is a physiological instrument designed originally in the 1860s to study interrelationships between the respiratory system, pulse rate and muscle nerve reaction.