This paper is an experimental study of the convective instability of a jet. It is well known that a jet issuing forth from a nozzle is unstable due to surface tension forces that cause it to break downstream into drops. We apply a disturbance of a given frequency at the nozzle tip. This applied frequency determines the wavelength and the growth rate of the growing disturbances and, thereby, the drop size. We measure the wavelength and the growth rate by fitting the entire digitized image of a jet to the functional form suggested by the linear theory. Thus, it makes use of the entire profile instead of the small number of points used in previous studies. Also, in contrast to previous work, we independently measure the jet velocity and the wave speed. At high non-dimensional jet velocity, the experimental results for the growth rates and the wave numbers agree with the linear stability theory of an infinite jet in the absence of gravity. At very low velocity (low Froude number) gravity is important and the agreement is not good. (C) 2003 Elsevier Science Ltd. All rights reserved.