We propose to consider the spatial form of a quasi-normal modes with allowance for their time dependence. Doing in this way one can escape the exponential rise of quasi-normal modes at spatial infinity.

The eigenfrequencies of a dielectric sphere are complex $\omega
=\omega'-i\, \omega''$, where $\omega '$ is the free oscillation (radian) frequency and $\omega ''$ is its relaxation time. These modes can be classified as the interior and exterior ones and, at the same time, as volume modes and surface modes.

In physical applications the surface modes turn out to be important, for example, when estimating the health hazards due to the use of portable telephones. The point is the eigenfrequencies of a dielectric sphere with physical characteristics close to those of a human head lay in the GSM 400 MHz frequency band which has been used in a first generation of mobile phone systems and now is considered for using again. In this situation one can assume that the surface modes excited by a cellular phone will lead to higher heat generation in the tissues close to a head surface as compared with the predictions of routine calculations in this field.

The layout of the paper is as 