The microscope alone is capable of detecting at one operation the nature and extent of the more harmless but general of these frauds. When once the investigator, by the aid of that instrument, has become familiar with the configurations of different kinds of the same chemically composed substances, he is armed with far greater detective power than chemical agents could provide him with. It is beyond the limit of the test-tube to show the mind the various forms of animal and vegetable life which exist in impure water; delicate as are its powers, it could not indicate the presence of the sugar-insect, or distinguish with unerring nicety an admixture of the common Circuma arrowroot with the finer Maranta. Chemistry is quite capable of telling the component parts of any article: what are the definite forms and natures of the various ingredients which enter into a mixture, it cannot so easily answer. This the microscope can at once effect; and in its present application consists Dr. Hassall's advantage over all previous investigators in the same field. The precision with which he is enabled to state the result of his labours leaves no appeal: he shows his reader the intimate structures of a coffee-grain, and of oak or mahogany sawdust; and then a specimen of the two combined, sold under the title of genuine Mocha. Many manufacturers and retailers who have been detected falsifying the food of the public, have threatened actions; but they all flinched from the test of this unerring instrument.