A Letter published in the Journal (Vol. IV, No. 2, p. 211) from Captain Brett Hilder refers to the use of the phenomenon known as the green flash for obtaining longitude at sea, and an editorial comment on the letter suggests that accurate descriptions of what has actually been observed at different times at sea might be of value to meteorologists. The following notes, though they contain no reference to using the observations for navigational purposes, may be of some interest as they are the result of a great many observations of the phenomenon.

Numerous reports on observations of the green flash have been published in meteorological publications where, as a general rule, it is accepted that it is only seen under conditions of extreme visibility and clearness of the atmosphere. From numerous personal observations it has been ascertained that this is in fact not so, and that the green flash can be observed under conditions of extreme cloudiness, haze and humidity so long as the horizon is visible at the time of rising or setting of the heavenly body. Another factor affecting the actual sighting of the green flash is the intensity of light emanated by the body, for the flash is of very weak intensity when compared to the normal brilliance of the body observed.