There is a great difference between merely viewing an object by the microscope, and investigating its nature: in the first, we only consider the magnified representation thereof; in the second, we endeavour to analyse and discover its nature and relation to other objects. In the first case, we receive the impression of an image formed by the action of the glasses; in the second, we form our judgment by investigating this image. It is easy to view the image which is offered to the eye, but not so easy to form a judgment of the things that are seen; an extensive knowledge of the subject, great patience, and many experiments, will be found necessary for this purpose: for there are many circumstances where the images seen may be very similar, though originating from substances totally different; it is here the penetration of the observer will be exercised, to discover the difference, and avoid error.[40] [40] Fontana sur les Poisons, vol. ii, p. 245. Hence Mr. Baker cautions us against forming too suddenly an opinion of any microscopic object, and not to draw our inferences till after repeated experiments and examinations of the objects, in all lights and various positions; to pass no judgment upon things extended by force, or contracted by dryness, or in any manner out of a natural state, without making suitable allowances. The true colour of objects cannot be properly determined when viewed through the deepest magnifiers; for, as the pores and interstices of an object are enlarged, according to the magnifying power of the glasses made use of, the component parts of its substance will appear separated many thousand times farther asunder than they do to the naked eye; it is, therefore, very probable, that the reflection of the light from these particles will be very different, and exhibit different colours. Some consideration is also necessary in forming a judgment of the motion of living creatures, or even of fluids, when seen through the microscope; for as the moving body, and the space wherein it moves, are magnified, the motion will also be increased. If an object be so opake as not to suffer any light to pass through it, as much as possible must be thrown on its upper surface, by that part of the apparatus which is peculiarly adapted to opake objects. As the apertures of deep magnifiers are but small, and consequently admit but little light, they are not proper for the examination of opake objects: this, however, naturally leads us to our second head. OF THE MANAGEMENT OF THE LIGHT.