When the configurations are fully formed, and all the water evaporated, most kinds of them are soon destroyed again by the moisture or action of the air upon them; their points and angles lose their sharpness, become uneven and defaced, and moulder as it were away; but some few are permanent, and by being inclosed between glasses, they may be preserved months or even years.
It happens oftentimes that a drop of a saline solution can hardly be spread on the slip of glass, by reason of the glass’s smoothness, but breaks into little globules, as it would do were the surface greasy: the way to prevent this is, by rubbing the broken drop with your finger over the glass, so as to leave the glass smeared with it; on which smeared place, when dry, another drop of the solution may be spread very easily in whatever form is agreeable.
It sometimes happens, that when a heated drop is placed properly for examination, the observer finds such a cloudiness that he can distinguish nothing of the object; which is owing to saline steams that arise from the drop, covering and obscuring the object glass, and therefore must immediately be wiped away with a soft cloth or leather.
In all examinations of saline solutions by the microscope, even though made in the day-time, you must use a candle; for the configurations, being exceedingly transparent, are rendered much more distinguishable by the brown light a candle affords, than by the more white and transparent day-light; and besides, either by moving the candle, or turning the microscope, such light may be varied or directed just as the subject requires.
It may be also proper to take notice, that no kinds of microscopes are fit for these observations, but such as have an open stage, whereon the slips of glass, with the liquor upon them, may be placed readily, and in a perfect horizontal position; and moreover, where they can be turned about freely, and without disordering the fluid.
CHAP. V.
THE IMPORTANCE OF NATURAL HISTORY; OF INSECTS IN GENERAL, AND OF THEIR CONSTITUENT PARTS.
There is no human science which to a rational mind exhibits a greater variety of attractions, or which is more deserving of general esteem, than that of NATURAL HISTORY; accordingly we find, that from the earliest times in which the sciences have been promulgated, it has never been entirely destitute of its votaries; but, on the contrary, has for ages employed the lives of many learned men, as being, in fact, the study of DIVINE WISDOM displayed in the creation: the farther our researches are carried, the more striking proofs of it every where abound. In the present century, an æra particularly devoted to investigation, and propitious to discovery and improvement in various branches of science, Natural History, so far from being neglected, has been more generally cultivated, and pursued with an ardor unprecedented at any former period. Men of the first rank in literature have become indefatigable labourers in the vast and unbounded field which it presents to the eyes of an accurate and attentive observer. The animal, the vegetable, and the mineral kingdoms, have been examined with the utmost care; that confusion and perplexity which seemed unavoidably to result from a view of the immense variety of articles contained in each of those departments, and which frequently deterred persons from engaging in the pursuit, have been in a great measure removed by the introduction of systematic arrangement; by these means, the various subjects are distributed into classes and genera, enabling us to form distinct and comprehensive ideas of them. To the same methodical plan, and the nicety of discrimination thence arising, we must attribute the discovery and description of many new species; this has excited an emulation still farther to pursue the inquiry, nor need any apprehension be entertained that the subject will be exhausted, as, no doubt, an infinite variety still remains unexplored to engage the utmost attention of the philosophic mind, and fully to compensate the pains bestowed on so interesting a branch of knowledge.
Of the abundance of articles enumerated in books of Natural History, there are comparatively few, whose uses are as yet known, or their properties fully understood. The true naturalist should always bear in mind that there is a vast difference between retaining the names, and investigating the nature and peculiar qualities of the creatures to which they belong. It is highly proper, indeed necessary, that the multifarious objects of Natural History should be well ascertained and distinguished with nicety in all their varieties; the science and admirers of it are, therefore, unquestionably indebted to the able naturalists who have devoted their time, and exercised their ingenuity in devising commodious methods of arrangement, and invented systems for identifying the several subjects with accuracy, and less danger of fallacy or mistake: but all who are, or would wish to be thought naturalists, ought to consider, that the best possible mode of classification is, after all, but an introduction to Natural History. The ingenious and indefatigable Linnæus, who spent his life in fabricating the curious system now generally adopted, intended it certainly for the improvement of the science, as a basis for the service of knowledge and the benefit of mankind; let us be cautious not to mistake the means for the end, but in the prosecution of the science, think of the true ends of knowledge, and endeavour to promote our own instruction, and the advancement of others, with a view to the adoration of that DIVINE BEING to whom all creation is indebted for existence, and their application to the occasions and uses of life, all along conducting and perfecting the study in the spirit of benevolence.
The study of nature, or in other words, a serious contemplation of the works of GOD, is indeed a great and proper object for the exercise of our rational faculties; nor can we perhaps employ them better, than in endeavouring to make ourselves acquainted with the works of that glorious Being from whom they were received.