Young (P) contracted to repair a bridge for the City of Chicopee (D). P's compensation was to be measured by the number of feet of new lumber used on the bridge. The contract provided that at least one-half the materials were to be on the job before work could begin. Lumber not in use was spread about the bridge and upon the riverbanks. The bridge was destroyed by fire without fault of either of the parties. Part of the unused lumber was destroyed. D did not dispute its liability for the work done but refused payment for the destroyed and unused lumber.