Short and Easy Methods for Finding (1.) The Quantity of Time Contained in Any Given Number of Mean Lunations; (2.) The Number of Mean Lunations Contained in Any Given Quantity of Time; (3.) The Number of Troy Pounds Contained in Any Given Number of Avoirdupoise Pounds, and Vice Versa; (4.) The Quantity and Weight of Water Contained in a Full Pipe of Any Given Height, and Diameter of Bore; And Consequently, to Find What Degree of Power Would be Required to Work a Common Pump, or Any Other Hydraulic Engine, When the Diameter of the Pump-Bore, and the Height to Which the Water is to Be Raised Therein, are Given. Communicated by Mr. James Ferguson, F. R. S.