We report the first observation of axisymmetric solitary waves on the surface of a cylindrical magnetic fluid layer surrounding a current-carrying metallic tube. According to the ratio between the magnetic and capillary forces, both elevation and depression solitary waves are observed with profiles in good agreement with theoretical predictions based on the magnetic analogue of the Korteweg-deVries equation. We also report the first measurements of the velocity and the dispersion relation of axisymmetric linear waves propagating on the cylindrical ferrofluid layer that are found in good agreement with theoretical predictions.PACS numbers: 47.65.Cb,47.35.Fg Solitary waves or solitons are localized nonlinear waves that propagate almost without deformation due to the balance between the nonlinearity and the dispersion. Since the first observation of a solitary wave on the freesurface of water by Russel [1], and its interpretation using the Korteweg-de Vries equation (KdV) [2], it has been shown that the KdV equation describes a large class of solitons observed in various situations: acoustic waves on a crystal lattice, plasma waves, hydrodynamics internal or surface waves, elastic surface waves, and waves in optical fibers [3]. Most of them involve a localized elevation disturbance propagating within a quasi-one-dimensional plane system. Observations of axisymmetric solitary waves governed by the KdV equation are scarce [4], and mainly concern waves in rotating fluids confined in a tube or on vortex lines. More recently, Bashtovoi et al. derived a KdV equation with an axisymmetric solitary waves solution propagating on the surface of a cylindrical magnetic fluid layer submitted to a magnetic field [5,6]. Without gravity, the stability of the cylindrical magnetic fluid layer is governed by the ratio between the magnetic force and the capillary one. According to its ratio, axisymmetric elevation (hump-like) or depression (hole-like) solitary waves are predicted with a subsonic or supersonic velocity [5,6]. To our knowledge, direct observation of axisymmetric magnetic solitary waves have never been reported.In this Letter, we report the first observation of axisymmetric solitary waves on the surface of a cylindrical ferrofluid layer submitted to an azimuthal magnetic field. Depending on the strength of the field, elevation or depression solitary waves are observed on the ferrofluid surface. A ferrofluid is a stable suspension of nanometric magnetic particles diluted in a carrier liquid (water or oil) that responds to an external applied magnetic field [7,8]. Although the solitary waves are damped by viscous dissipation, we have shown that they keep the self-similar profile given by the solution of the KdV equation on a propagation length larger than their typical scale. Moreover, we also report the first measurement of the velocity and dispersion relation of axisymmetric magnetic linear waves in this system in good agreement with the theoretical predictions [9].The experimental setup is shown in Fig. 1. It consists...