Two models of a liquid-hydrogen (?-illegible) Cherenkov counter (illegible) been constructed (illegible). The first served as a prototype (?-illegible) and was (illegible) to demonstrate the feasibility (?-illegible) of the (illegible) concept (?-illegible) (illegible) liquid hydrogen does not give scintillation (?-illegible) (illegible) that of Cherenkov light. The second, final version (?-illegible), (illegible) in an experiment (?-illegible) in which particles brought to rest (?-illegible) (illegible) (illegible) electrons. In this second counter, the efficiency (?-illegible) (illegible) relativistic (?-illegible) particles (?-illegible) by their Cherenkov radiation in liquid hydrogen (?-illegible) was measured by stopping (illegible) mesons in the hydrogen and detecting their decay electrons outside (?-illegible) of the flask (?-illegible) after a suitable time delay. An average detection (?-illegible) efficiency (?-illegible) of 75% (?-illegible) was (illegible) taken over the volume of the hydrogen (?-illegible).