We have received a letter from Mr. Philip O'Reilly, of Providence, R. I., in which he states that lime is of no avail in preventing potato rot, as he has tried it, and has seen it it tried by others in vain. After many experiments, he has found that a handful of dry peat in powder or in small pieces was the best preventive, and he thinks if it were generally applied, it would'save ninety-nine in every hundred hills. This experiment can easily be tried. Those farmers who cannot get peat may use swamp muck, which is nearly as good. While we advise our readers to be up and doing, in trying experiments, we exhort them always to count the cost first. Various specifics have been recommended as preventives of the potato disease ; but we must enjoin caution against relying positively on any one presented. A certain specific may be a remedy in one situation, or in one season, and not in another, just like medicine as applied to the genus homo.