We study the extinction properties of dust in the well-defined dust lanes of four highly inclined galaxies using U-, B-, V-, R- and I-band CCD and J- and K'-band Near-Infrared array images. For three of these galaxies, we could use the symmetry of the underlying light profile to obtain absolute extinction values in the dust lanes. Maximum values

IAUC 6072 available at Central Bureau for Astronomical Telegrams. IAUC 6072 available at Central Bureau for Astronomical Telegrams.

We classify non-trivial (non-central) extensions of the group $Diff^+(S^1)$ of all diffeomorphisms of the circle preserving its orientation and of the Lie algebra $Vect (S^1)$ of vector fields on $S^1$, by the modules of tensor-densities on $S^1$. The result is: 4 non-trivial extensions of $Diff^+(S^1)$ and 7 non-trivial extensions of $Vect (S^1)$

EN ESTE TRABAJO SE PRESENTAN LOS RESULTADOS DEL ANALISIS DE OBSERVACIONES FOTOMETRICAS Y ESPECTROSCOPICAS DE SIETE DE LAS OCHO BINARIAS QUE CONSTITUYEN EL SUBGRUPO DE SISTEMAS RS CVN DE PERIODO CORTO, ASI COMO DE OTROS DOS SISTEMAS DE PERIODO MAS LARGO PERTENECIENTES AL SUBGRUPO LLAMADO "CLASICO" DE LOS SISTEMAS RS CVN. LAS OBSERVACIONES

IAUC 6065 available at Central Bureau for Astronomical Telegrams.

A procedure to compute meteoroid spatial number densities from photographs is presented. It follows from the visual method of Koschack and Rendtel with slight changes. Some parameters are recomputed and hints are given on how to produce useful photographic observations. Finally, an analysis of the expected errors is performed.