On the resolving power of photographic plates

.—The convenience of the photographic plate as a recording instrument, in that it not only makes a record but also integrates impressions which are individually too faint to be observed, is so manifest that to a continually greater extent physicists are designing instruments for use solely or chiefly by photographic methods. It is curious to note that while the resolving power of physical instruments generally has been completely investigated, very little indeed has been published upon the resolving power of the plates used as recording instruments.