So in those fearful days we worked with the recording instruments, watching them at each new trial for some indication of the force whose source we sought. The whole great mass of New York's giant structures that stretched southward and downward from our laboratory lay now in complete darkness each night; the last wonted activities of civilization having ceased in it as elsewhere. Ragged hordes of savages roamed it, savages so hairy and crouching and brutal of face, seeming each day more prognathous of jaw and slanting of brow and animal-like of eye, that we knew them to be troglodytes, cave-men, men such as humanity had been ages before and such as it was over all earth now. We saw them occasionally prowling through the university grounds in search of food, shambling toward us with lowering brows to attack us when they glimpsed us, but fleeing in fear when we fired over their heads. For none of them could manipulate so complicated a thing as a firearm. All earth's hundreds of millions were prowling their way in just such brutal bands, thrown back to the state that had been man's before history's dawn. And ever more brutal and hairy and animal-like they were becoming as they slipped back farther still, back from troglodyte to ape! Mankind was gone, transformed into these still-changing brutes--all except Ferson and me. * * * * * I cannot tell now in full of those terrible last days of change, those days in which in our chance glimpses we saw men making that other terrible step backward, from troglodyte to ape. For Ferson and I were working with the speed of utter despair. Even were Grant's terrible work to be halted, the sun's evolution vibrations again released on earth, it would take them untold ages to raise the brute-like beings about us to the status of men once more. Humanity was passing, had passed, into the brute around us, yet for their sake, for the sake of the humanity that might rise again in the dim future, we kept to our efforts, sought still to halt this awful change, that would otherwise not stop until protoplasmic slime alone was left living on earth. We had found the correct frequency for the circuits of our recording instruments, and in feverish haste set up those instruments at intervals of a mile, working through the night. The weirdest of work it was, the vast city's streets and structures silent in the night around us, the countless hordes of brute-like beings that once had built them now cowering in the buildings in ape-like fear of the night's mysteries. We took our readings, hastened back to our laboratory, and dawn found us marking those readings on the great chart-map of the section we had ready. Somewhere in that section, somewhere near New York, we knew, Grant lurked with his terrible mechanism, our first readings having shown us that. And now, as with trembling hands Ferson and I drew the graphs on the big chart, we stared for a moment after in complete silence.