The Collaborative International Dictionary
Perceptibleness
Perceptible \Per*cep"ti*ble\, a. [L. perceptibilis: cf. F. perceptible. See Perceive.] Capable of being perceived; cognizable; discernible; perceivable.
With a perceptible blast of the air.
--Bacon.
[1913 Webster] -- Per*cep"ti*ble*ness, n. --
Per*cep"ti*bly, adv.
Wiktionary
perceptibleness
n. The state of being perceptible.