Infrared technique was used to visualize cross-flow vortices on a 7° half-angle sharp cone at an angle of attack of 6.6°. The measurements were made in the Mach 6 hypersonic Ludwieg tube Braunschweig of the Technische Universität Braunschweig. Surface pressure-sensors gave additional information of the frequency and the position on the cone of second-mode instabilities. The combined data was used to identify the surface regions where laminar-turbulent transition was caused by second-mode instabilities. Relative N-factors were computed along the footprints of the cross-flow vortices. These N-factors were modified by the placement of artificial roughness elements on the cone's surface.