The square root of the frequency of these photons  increased from one target to the next in an arithmetic progression.
ðə skwˈɛɹ ɹˈuːt ʌvðə fɹˈiːkwənsi ʌv ðiːz fˈoʊtɑːnz ɪŋkɹˈiːst fɹʌm wˈʌn tˈɑːɹɡɪt tə ðə nˈɛkst ɪn ɐn ɚɹˈɪθmətˌɪk pɹəɡɹˈɛʃən.