sometimes , as when he had been trailing his fingers over the slightly pebbled surface of the stand in which the memorial park birdbath was set , or when he had squatted down to look more closely at the trolley tracks which grooved mont street in the old cape , he would be struck by a profound sense of time ... time as something real , as something that had unseen weight , the way sunlight was supposed to have weight ( some of the kids in school had laughed when mrs greenguss told them that , but mike had been too stunned by the concept to laugh ; his first thought had been , light has weight ?