Reported here is a study of the transmission of magnetosheath hydromagnetic fluctuations with f~23 mHz and f~13 mHz through the magnetopause. The study involves measurements of the fluctuations inside the magnetosphere on the ISEE 2 spacecraft near the equator and on the ground near the boundary flux tube connecting with spacecraft. The magnetic energy of the fluctuations inside the magnetopause is about 1% of those in the magnetosheath. This ratio is consistent with that expected for the transmission of fast-mode waves through a magnetopause with a tangential discontinuity. Just inside the magnetopause the fluctuations are right-hand elliptically polarized as measured both on the spacecraft and on the ground. About 10% of the near-magnetopause energy at 13 mHz is measured on the ground at L~2.6. It is uncertain, from present theoretical concepts, how such high energy levels are produced so deep into the magnetosphere as a result of surface wave attenuation. ¿ American Geophysical Union 1989