Abstract
The new 13-color medium-narrow band photometry published by Johnson and Mitchell has been used to investigate the law of interstellar extinction in several regions of the sky. The extinction laws in these regions are different, and must indicate that there are physical differences of the interstellar material which produces the extinction in the several regions studied. Nevertheless, n value of R = Av/E (B-V) = 3.24 0.2 (p.e.) probably is satisfactory for statistical investigations in our Galaxy. The value of R in the region of the Orion Nebula has again been found, to be much higher; and it seems likely that high values of R will be found in regions where 0-type stars are imbedded in nebulae. Key words: INTERSTELLAR: REDDENING - EXTINCTION - PHOTOMETRY.
