You may sometimes find that the actinometer indicates a very different exposure from what the eye would lead you to expect.
"Scientific American Supplement, No. 492, June 6, 1885" by Various
For judging long exposures, the use of an actinometer (issued in many inexpensive forms) is helpful.
"How to Observe in Archaeology" by Various
Exposure must be judged by an actinometer.
"Photogravure" by Henry R. Blaney
It is a good plan to employ an actinometer to judge the correct exposure.
"Photographic Amusements, Ninth Edition" by Walter E. Woodbury and Frank R. Fraprie
PRINTING WITH AN ACTINOMETER.
"The Barnet Book of Photography" by Various