The most delicate test objects for microscopes are the lines on the feathers of butterflies or moths' wings, of which there are many gradations; some easily demonstrated, and others only to be seen with the most powerful reflectors, and to the best advantage by the simple and uncondensed light of the lamp. The hair of a mouse is a very good test object: it is best seen by daylight; the most difficult parts of which are longitudinal lines in the transparent part of the hair, which require high powers. The hair of the bat and seal are also fine tests. The lines on the scales of the diamond beetle, &c. are excellent opaque proof objects. The feet of flies are likewise very interesting.

New Lilac Dyes.

Dr. Macculloch has lately produced two fine lilac dyes from plants of domestic growth, not hitherto applied to this purpose. One is from the berry of the Portugal laurel, and the other the black currant. The simplest process with alum is all that is required for either; and as far as his trials go, the best tint is produced by the former fruit.

Dirty Windows.

We have frequently remarked small radiant and arborescent crystallizations on dirty windows in London, and have found them to consist of sulphate of ammonia. This salt, or at least, sulphite of ammonia (which becomes sulphate by exposure to air), is an abundant product of the combustion of coal.

Brande's Journal.

Indigo.

This valuable plant, which gives rise to as great speculation in India, as hops in England, is much injured by wet weather; although the rapidity of the growth of plants during much rain, in the temperature of the tropics, is extraordinary, yet a proportional deficiency in all that characterizes the vegetable world necessarily follows. This we find to be the case with all forced vegetables; and the mildness of the radish of hastened growth, when contrasted with the highly pungent and almost acrid flavour of the slowly and gradually advanced one, may be adduced as explanatory of this observation. Hence, it is practically well known to manufacturers, that the indigo plant, however fine and luxuriant, as is the natural result of much rain, is very deficient in produce, and a similar loss is experienced even if the plant, without the fall of too much rain, has grown up under cloudy weather. Sunshine, much and continued sunshine, is essentially necessary for the proper exercise of those secretory organs by which this peculiar drug is formed and perfected.

Indigo leaves produce two dyes—blue and yellow; but the refuse leaves, when boiled for an hour and a half, will render the water yellow, tinged with green. This water, kept boiling for two hours, (supplying the loss by evaporation), will, when filtered, afford a precipitate, which, when dried, will in colour be a dun-slate, and in quantity perhaps about equal to the blue extract such leaves have produced. This observation, as it can lead to no practical advantage, is made for the man of science, rather than the man of business.—Mr. C. Weston—in Brande's Journal.

Chain Bridge.

Mr. Disney has lately erected at his seat the Hyde, Ingatestone, Essex, a suspension bridge of common chain, which is much cheaper than either wood or brick. It is fifty feet long, and four feet wide. The whole cost of material, and workmanship scarcely exceeded 30l. Upon a rough estimate, a wooden bridge of the same span would have cost from 80l. to 100l., and a high arch probably from 150l. to 200l. The piers or posts supporting the chains are of oak, but should they in ten or fifteen years decay, 10l. in money, and three days in time would set it up again.—Brande's Jour.

Stone Roofs.

The Romans employed pumice in building their arched incombustible roofs. This porous material possessed the additional advantage, when combined with good cement, of rendering the arched surface one united petrifaction, opposing (in consequence of its firm union) little lateral pressure, comparatively, against the sustaining walls.

Bonomi, the architect, suggests that the principal cause of the destructiveness of fires in large buildings, is the want of arched surfaces of incombustible materials. This has been disastrously exemplified in the destruction of the choir of York Minster, where the roof of the aisles, which are solidly arched with stone, suffered no injury; while the choir-roof, although much more raised above the action of the fire, has been entirely destroyed by it.

Fossil Saurians.

Several beautiful specimens of fossil saurians, or animals of the lizard tribe, have, as our scientific readers are aware, been found at Lyme, in Dorsetshire; but the world would to this day have remained ignorant of the treasures England possessed, but for the patient labours of three female pioneers in this service, viz. Mary Anning, a dealer; Miss Congrieve, and Miss Philpots, residents, who for years had been collecting and preserving these bodies from the wreck of the coast; the two last without any other view than the gratification of a laudable curiosity, and who, with unequalled liberality, communicated their collections to every man of science that visited the place; and it is to liberal minds like theirs, and Miss Bennet's, of Wiltshire that we owe the first rescuing of these natural gems from the spoilers. We copy this from a communication of Mr. Cumberland to Brande's Journal, and are truly pleased to record such amiable examples of female excellence in scientific pursuits. At Dover, Portsmouth, and other places we could name, we obtained the best information respecting the fossils of the coast, from females resident there, and we need not add that this circumstance imparted additional interest to our inquiries.

The Zoological Society.

We copy the following from the Report to the Zoological Society, just published:

"In the Museum in Bruton-street various improvements have taken place. Additional cases have been erected, wherever space could be obtained, for the exhibition of the different collections; and two persons have been in constant employment in preparing and setting up the more interesting specimens. An assistant has also been lately added, for the arrangement of the shells, insects, and the other smaller subjects of the collection; and much care has been bestowed upon the various departments of comparative anatomy. An instructive as well as an attractive series in every branch of zoology, but more particularly in the groups of mammalia, birds, and insects, has thus been arranged for inspection. A catalogue of the more important objects in the Museum has been published; and a more detailed list, accompanied with scientific notices of all the species, is in preparation.

"The increase in the number of subjects in the collection during the last year has been considerable, and many of the additions have been of the utmost importance to science. The whole of these, with a few exceptions, have been presented by the friends of the society. A detailed list of these donations which are too numerous for insertion in this report, is laid upon the table; a reference to the contents of which will evince that the spirit of liberality, which laid the foundations of this already valuable collection, has not decreased.

"A very extensive correspondence has been established with naturalists of foreign countries, and persons resident in distant parts, who are anxious to promote the objects of the Society. Through these channels many valuable acquisitions have been already received; and it is expected that much of novelty and interest will continually pour in to increase the attractions of the Museum and Menagerie.

"The Garden in the Regent's Park is the principal source of attraction and of expense. The nature of the soil, which consists of a thick ungrateful clay, increases the cost of every work. The health of the animals requires that oak floors be raised above the surface of the ground; and it is necessary to lay a thick substratum of dry material under every inclosure and every walk. These disadvantages are however amply counterbalanced by its immediate vicinity to the town. The Council have, notwithstanding the nature of the soil, endeavoured to give to the garden all the attractions which good cultivation and an abundance of flowers can afford: and they have to return their thanks for the very liberal supplies for this purpose which they have occasionally received from the Horticultural Society. The resort to the garden has far surpassed the most sanguine expectations of the Council; 112,226 persons have visited it during the last year."