Invisible.—Naturalists suppose another species or order of invisible animacules, viz., such as escape the cognizance even of the best microscopes, and give many probable conjectures in relation to them. Reason and analogy give some support to the existence of infinite imperceptible animalculae. The naked eye, say some, takes in from the elephant to the mite; but there commences a new order referred only for the microscope, which comprehends all these from the mite to those 27 millions of times smaller; and this order cannot be yet said to be exhausted, if the microscope be not arrived at its last perfection. See further on this subject the article MICROSCOPE.