On the colour excesses of the long-period cepheids.

Photometric measurements have been made on the uvby system of stars located in the fields near five long-period Cepheids. The interstellar reddening of these field stars is compared with published data for the Cepheids. It appears that for the longest period Cepheids (periods greater than about 15 days) systematic errors exist in the methods of finding colour excesses which seriously affect the pulsational masses.