The speed of sound
in helium was measured along five isotherms
in a temperature range from 273 to 373 K at pressures from 15 to 100
MPa with a relative expanded uncertainty (k= 2)
from 0.02 to 0.04%. A dual-path pulse-echo system was utilized to
conduct these measurements. The data were compared with the reference
equation of state developed by Ortiz Vega et al. At pressures up to
50 MPa, relative deviations were within the uncertainty of our measurements,
while, at higher pressures, increasing negative deviations were observed
up to -0.26%. We also compared the results with predictions based
on the virial equation of state correct to the seventh virial coefficient,
using theab initiovirial coefficients reported
recently by Gokul et al., finding agreement to within the experimental
uncertainty at all investigated states.