This farmer's weather-glass, then, consists of three distinct instruments: the barometer, the thermometer, and the hygrometer. He has thus at command the three instrumental data necessary for the prediction of the weather. And now to describe-- _How to Use the Instrument._--The observations should be taken twice a day, say at 9 A.M. and 3 P.M.; and should be entered on a slip of paper, or a slate hung up by the barometer. The observer will then be able to see the different values of the readings from time to time, and to draw his conclusions therefrom. The thermometer on the left hand should first be read, and a note made of its indication, which is the temperature of the air. The wet bulb thermometer should now be read, and also noted; and the difference should be taken of these two readings. Next read the barometer by moving the small index at the side of the tube until it is on a level with the top of the mercury. Having noted the number of inches at which the column stands, compare with the last observation, and see immediately whether the barometer is rising, steady, or falling. Now, having taken the observations as above, we naturally ask the question, _What are we to predict from them?_ And, probably, the best way of answering this query will be by giving an example. We will suppose that our readings yesterday were as follows:--Temperature, 70 deg.; Wet Bulb, 69 deg.; Difference, 1 deg.; =very moist air. Barometer, 29.5, and that rain has fallen. To-day, we read:--Temperature, 60 deg.; Wet Bulb, 55 deg.; Difference, 5 deg.; =dryer air. Barometer, 30. We may safely predict that the rain will cease, and probably we may have wind from the northward. In spring or autumn, if the barometric height be steady any where between 29.5 and 30 inches, with the temperature about 60 deg., fresh to moderate south-westerly winds, with cloudy sky, will probably characterize the weather; the indications of the hygrometer being then specially serviceable in enabling us to foretell rain; but if the mercury become steady at about 30.5 inches, with temperature about 40 deg., north-easterly winds, dry air, and clear sky, may be confidently expected. Many cases will doubtless suggest themselves to the observer where these figures do not occur, and where he might find a difficulty in interpreting the indications of his instruments. We have, therefore, drawn up some concise rules for his guidance; and although they will not prove absolutely infallible guides to this acknowledged most difficult problem, still, they will be found of much service in foretelling the weather, when added to an intelligent observation of ordinary atmospheric phenomena, as force and direction of wind, nature of any particular season, and the time of year. 26. RULES FOR FORETELLING THE WEATHER. A RISING BAROMETER. A "Rapid" rise indicates unsettled weather. A "Gradual" rise indicates settled weather.