Measurement of the HiRes Stereo Composition

Extensive air showers are induced when ultra-high energy cosmic ray particles enter the Earth's atmosphere. The distribution of depths where the number of particles in the air showers reach a maximum (defined as $X_{max}$) can be used to measure the composition. We present a method of directly measuring the flux of various hypothesized compositions by comparing Monte Carlo calculations of $X_{max}$ with the distribution of $X_{max}$ for data.