A discussion of the new variations observed in the nucleus of the Seyfert galaxy NGC 3516.

. We present new spectroscopic observations (19701971) of the Seyfert galaxy NGC 3516. Through the comparison with previous observations (1967) performed in the same conditions, we essentially deduce: - an enhancement of the Balmer lines (the intensity is about four times larger) - a decrease of the intensity of the [0 iii] line 4363 - no variations of the continuum in the range 40006000 A. The emissive region is composed of two or three different zones, with densities 108 to 1O -1O and masses from 2-200 M0 - A model with a clumpy distribution for the emissive gas accounts for the observed variations better than an homogeneous model (previously suggested by Souffrin, 1969a and b). A variable central source of UV radiation or more likely soft X-rays provides the heating. The line variations can be explained by variations in the total numbers of emitting particles. The ionized regions must then contain neutral or weakly ionized matter. An attempt is made to explain such variations over a period of three years at most. Key words: Seyfert galaxy nucleus - variations - emission lines - continuum - stellar population