As this experiment was made with a fluid of 8° strength, so for the sake of greater certainty, several experiments were performed, both with stronger and weaker fluids, and the results corresponded exactly with the above: for instance, with a fluid of 14° strength, the thermometer, at the commencement of the distillation, stood at 63°, and the strength of the spirit was 16°; the instrument continued stationary, until the spirit, which came over, was weaker, when it rose gradually in the foregoing proportion.

On the other hand, when the strength of the liquor is only 4°; at the beginning of the operation the thermometer stands at, and the product is 14°, but afterwards follows by degrees the preceding proportions.

The experiments, performed many times, and always with the same result, gave rise to the following results:

1. A person may, by the state of the thermometer, immediately ascertain the strength of the liquor in the vessel.

2. There is no necessity of using the alkohometer in distillation, as the preceding account shews that the thermometer indicates the strength of the liquor with equal accuracy.

3. Without drawing off any spirit, what quantity there is of any particular strength may be immediately known.

4. Every possible fraud, during the operation, may be prevented, as the apparatus can either be locked up, or brought into an adjoining apartment, for the person who attends the work does not require the thermometer to direct him.

With a larger apparatus of 200 pots, the thermometer differed much from the preceding scale, which probably was caused by its not being perfectly free from air; this, however, does not refute the accuracy of the above mentioned results. A person may, at the first trial with each apparatus, immediately form a scale for himself.

Although this discovery has only been tried with Mr Groening's apparatus, it is nevertheless his opinion, that a proper application of the thermometer to an apparatus, of whatsoever construction, will give the same results.

ART. VIII.-On Animals Preserved in Amber, with Remarks on the Nature and Origin of that substance. By J. MAC CULLOCH, M. D. F. R. S. Journ. Roy. Instit.]

THE value which has long been attached to the specimens of amber which contain insects, has introduced into the cabinets of collectors many imaginary examples of this occur rence, which a more careful examination would have proved to be fallacious. For the sake of those who may be inclined to purchase such specimens, or to reexamine their own acquisitions of this nature, it may be useful not only to suggest the frequent deceptions to which they are exposed by not attending to the real characters of the including material, but to point out an easy method of distinguishing the true from the false. It is the more necessary to do this, as the test which the Abbé Haüy has given in his work for this purpose, is neither satisfactory nor of easy application.

The existence of an insect in amber is an unquestionable proof of the vegetable origin of this remarkable substance, and is, therefore, in a mineralogical view, an important fact; but to find such an animal in the exudation of a living vegetable, is scarcely a subject of curiosity. It is in another respect, important to show, that such remains, if most frequently occurring in the recent resinous exudations, are not limited to them; since collectors, finding themselves deceived in their own specimens, might perhaps imagine that no genuine instance of an insect, actually preserved in amber, exists.

For the honor of dealers in specimens, it is, however, but just to remark, that the difference is not, or at least not generally, known to them; as among innumerable specimens exposed for sale, which I have examined, I have never yet found any of the proprietors aware of the distinction. False specimens seem, at any rate, to be true in their eyes, as they are in those of the purchasers. A very perfect state of preservation in such insects as may be surrounded by any substance resembling amber, is generally a justifiable ground of suspicion respecting the nature of the including material. It rarely happens that those insects preserved in amber are perfect; or that they present the more delicate part of the anatomy of the animal; the wings of the hymenopter, for example, or their delicate legs.

It would require too much nicety of observation for an ordinary naturalist, perhaps too much for any one, to decide on the recent nature of the including resin from the charac

ters of the insect contained in it: when it is considered how many insects are yet unknown, and how difficult it is to examine the enclosed specimens accurately. Otherwise, as there is abundant reason, from the analogy of other animal remains buried in alluvial matter, to conclude that insects enclosed in amber, have belonged to a former state of the globe, this difficulty might be solved by the entomological examination of the species. To ascertain the true nature of the including material, is a task of great comparative facility; and it is always sufficient for the purpose in view; that is, for ascertaining simply, whether the specimens consist of amber, or of some recent resin enclosing animal remains.

Where the exudation is sold in its natural state, the form of the lengthened mass, or drop, is generally a sufficient evidence of its real nature; as no amber is ever found which has not undergone some loss of shape from mechanical violence, or other causes, connected with its present mineral position.

But it frequently happens that this test becomes of no use; as the specimens are often cut and polished into such forms as to show the enclosed insect to advantage. Even in these cases, however, the colour and appearance of the resinous matter which encloses the insects, are always somewhat dif ferent from those of amber; or they are always at least such that a practised eye can pronounce on the genuine specimen ; can distinguish between resin and amber. A paleness of colour is invariable in the resin; and if amber is not always of a full yellowish brown, the paler varieties have a peculiar tinge of yellow which never exists in the resin; the colour of these is comparatively watery, thin, and feeble.

The striking character, however, to a practised eye, is a peculiar lustre in amber, which is wanting in the resin; arising probably from a higher refractive density, and easily recognized when once pointed out; but difficult to describe in words.

To those to whom characters of a nature so delicate are insufficient, it is necessary to point out other more unquestionable and easier modes of discriminating the two without injuring the specimens.

It is proper, in the first place, to remark, that the electrical property is not a sufficient test; although it is that to which an appeal is commonly made. The resins, like amber, are electrical on friction, and the electricity of both is negative. But on strongly rubbing the resins, they give out a smell quite different from that which is elicited from amber in the same circumstances. To describe odours, is evidently impossible;

but as they can never be mistaken for each other when once known, it will be necessary for the collector of specimens to render himself acquainted with both; by making the necessary experiments on genuine specimens of common amber, and on specimens of that resin which, if it is not the substance in question, agrees with it in its ostensible properties, namely, gum animi, as it is commonly called.

It would obviously be easy to supply chemical tests for the purpose of making this distinction; but the circumstances under which these specimens exist, are not such as to warrant their destruction for this purpose; and to ordinary collectors, any refined or minute mode of chemical examination would be useless. The only easy test which can be applied without destroying or materially injuring a specimen, is that of burning. If the doubtful specimen be held against a red-hot iron, the smell of the smoke which is produced, is always a sufficient distinction between the resins and amber; and to render this test of easy application, the collector may easily familiarize himself with the peculiar smells of the essential oils, which, with very slight differences, are given out by copal, gum animi, or the other recent resinous substances, and that of the oil of amber which is produced by burning this mineral. To this ultimate test, therefore, in doubtful cases, the collector of specimens may have recourse; and it will always be sufficient to distinguish from genuine specimens of insects enclosed in amber, those which have been entangled in the recent resinous exudation of trees. Haüy's differences between copal and amber, already alluded to, and which is founded on the different manner in which a melted drop falls from each, is neither so practical nor satisfactory.

I am sorry that I cannot inform your readers what is the real nature of the vegetable resin in question, which is commonly sold for amber when it contains insects. It has not been a matter of observation among the collectors of these specimens, or the dealers in them. Nor as far as the chemical analysis of vegetable compounds has yet proceeded, have we acquired any means of ascertaining by chemical means, the distinctions among these, more than among any other vegetable products, of which the general and ostensible characters are similar. It is, however, plain that it is not copal, at least in all cases; but it bears, as already insinuated, a striking resemblance to the gum known by the name of gum animi. That such insects should be contained in more resinous exudations than one is to be expected; and if those who are inclined to pursue this investigation should think it worth

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their trouble to make the necessary inquiries and experi ments, it will probably not be found very difficult to ascertain whether these specimens are limited to the produce of many trees, or to that of one only, and to what plant they actually belong.

The immediate object of this paper is included in the foregoing remarks; but the fact itself, as far as it relates to the existence of insects in amber, opens a different field of interesting inquiry, respecting which, unfortunately, no accurate information will probably ever be obtained.

Geological observations, recently multiplied to a most interesting degree, have proved, that besides the animals imbedded in deep seated strata of solid rock, and consisting of marine species, numerous remains exist in alluvial soils, of quadrupeds and birds which have once inhabited the dry land and the air, and of amphibious creatures that have been bred and have died where they have had alternate and easy access to the shores and to the waters of lakes.

It ought to be a sufficient proof of the corresponding, probably simultaneous, existence of insects, that they are found imbedded in amber; the only mode nearly in which they could have been preserved for the examination of the naturalists of future and distant ages, though some of the aquatic, or rather subaquatic, winged ones, have been found in the shales of the fresh-water formations. To render the proof of distance of time or of a corresponding era complete, it is only here necessary to advert to that which is already well known; namely, that amber is found in alluvial soils of an antiquity at least as remote as that which marks the other alluvial soils or strata in which such remains of a former living inhabited world are imbedded. That this should have been the fact, is too probable to doubt, even if such proofs did not exist. Whether specimens sufficiently numerous, and sufficiently distinct, may ever be found to enable some future Cuvier in entomology to assign the genera and species of such remains, is uncertain, perhaps it is not probable.

Hitherto, it is certain, that no sufficient attention has been paid to this branch of subterrene zoology, to the entomology of a former world. To clear the way to this investigation, by guarding against error in the specimens, is a humble step indeed. Yet to have called the attention of those who are versed in the minutiae of entomology to such a subject, will not be deemed officious in him who is unable to lend any further assistance towards that object. A careful examination of specimens may, perhaps, ultimately prove that more