Show malting making signals secret invisible light la is opening up it a new method of sending bending secret signals in wa warfare afi re flash signals are arc invisible to all but the receiver of tile the message and can be sent in full sunlight for a distance stance Pi of from five to eight miles infrared infra red rays too long to be seen cause certain dyes and pigments to become more luminous the receiver of the message Is equipped with a tinted shade for his field glasses similar ilar in color to the shade used in the signal lamp |