Data on specially intense solar flares from spectroscopic records (including recent spectrohelioscope observations) have been discussed in connection with the occurrence of magnetic storms. Certain features, including their great area and possible characteristics of spectrum, distinguish these very intense flares when they occur. Future observations should aim at including quantitative data to serve as an index of intensity. A geophysical measure of intensity should also be explored. Far more often than could occur by chance, an intense flare is followed about a day later by a great magnetic storm, provided that the flare is not farther than about 45° from the centre of the disk. Assuming that a corpuscular stream is newly ejected at the time and place of an intense solar flare, the mean effective time of travel of the stream from Sun to Earth is about 26 hours, the most intense magnetic storms giving a shorter travel-time of about 20 hours. The distribution on the Sun's disk of flares preceding great magnetic storms is examined and suggests certain features of the corpuscular streams involved.