Page:Hardwicke's Science-Gossip - Volume 1.pdf/156

Exotic Diatoms in British Localities.—The discovery of isolated valves of exotic diatoms does not prove that they ever lived in these isles. I have myself found (very sparingly) mixed with fresh-water forms species hitherto only detected in guano. In a gathering made from a small ditch, I found some fragments and one perfect valve of Aulacodiscus scaber, and also several valves of Triceratium alternans. Ne doubt these forms had been washed out of the adjacent fields, which had probably been manured with Peruvian guano. I had not cleaned any guano for many years. I have also occasionally observed marine and brackish-water species in washings from moss. In one gathering I detected a valve of Coscinodiscus radiatus and several valves of Pleurosigma Æstuarii. These must have been floating about in the air, and then brought down by the rain. We may fairly conclude that unless a species is found alive, and in tolerable plenty, it is not a native of the locality in which it is discovered, more particularly if the species are exotic. Thus, Arachnoidiscus has no claim to a British habitat. I believe only three valves have been found, one by M. de Brébisen, in a gathering from Ilfracombe, and described in the Synopsis of British Diatomaceæ, and two more twelve years after, by Mr. Archer. It is very desirable that all who make Diatoms their study should, before adding a new species to the large number already (and in many cases imperfectly) described, have found it plentiful and alive. To describe it correctly it must be examined living as well as dead. If the material is in sufficient quantity, a portion may be well washed with liquor ammonia, and afterwards with distilled water. By this means the stipes, or filaments, are preserved; and if the specimen is heated on the slide, it may then he mounted dry or in balsam (Aclinanthes longipes and brevipes are beautiful objects prepared in this way); a further portion may be acidized in the usual manner, as it renders striation more distinct.—Fred. Kitton, Norwich.

Guano, &c., in Exchange.—I shall be glad to exchange Upper Peruvian guano, Richmond earth, Nova Scotia earth, or China sea-soundings, rich in foraminifera, for any good foreign material containing diatomaceæ, or British gatherings of one species only.—W. J. B.

Scales on White Cabbage Butterfly.—Will any of your correspondents kindly inform me on what part of the white cabbage butterfly the elongated and tufted scales are found which are used as fest objects? I have never been able to find such as are described and figured by Quekett and others.—W. H. Reynolds.

Webster's Condenser (p. 90) is now being manufactured by a London optician. (See advertisement.)

Serpentine is used as a kind of marble. It is a silicate of magnesia, coloured very richly by metallic oxides, especially those of iron, nickel, and chrome. One kind, obtained from Cornwall, where the Lizard rock contains veins of extreme beauty, is remarkable for its brilliant red and mottled colour contrasted by veins of the purest white, and taking a very high polish. It is well adapted for small ornaments; bat when used for church work, such as fonts, internal columns, &c., its appearance is injured by its numerous veins and cracks. The polish, though brilliant, does not stand exposure to weather or damp air. The Italian serpentine (ophite) is a different mineral, and far less brilliant, the rich red tints being absent, and the colour generally mottled dark green. It is used, however, for similar purposes, and is of nearly the same value. It is comparatively soft, and very easily worked. Irish Connemara marble is a variety of serpentine, and is a very beautiful material for columns, tables, altars, and other decorative purposes. Its colour is much paler than the Tuscan, which it otherwise resembles.—Ansted's "Practical Geology."

Education in Geology.—There is no greater mistake in modern school tuition, and none so general, as the neglect of the natural sciences; and yet there are few departments of knowledge to which boys are more readily and earnestly attracted. The majority are naturally observers and collectors—as witness their little cabinets of birds' eggs, butterflies, and minerals; and it only requires encouragement and direction to make them reasoners and reflectors. If it be an important point in education to foster habits of observation and discrimination, then assuredly there is no theme se admirably adapted as the field of nature, and no section so accessible at all seasons as that of geology. It is true that the ordinary branches of tuition must ever occupy the main share of the schoolboy's attention; but there are intervals when natural history would be a recreation, and in that recreation the otherwise dormant mind might be first awakened to interest and energy. Get the mind by all means aroused to self-exertion; let it once taste the pleasurable excitement of knowing in one department, and the battle is won. The desire for further knowledge increases with the growth of that knowledge and strengthens with its strength. And even where such subjects as geology form no part of the regular curriculum, a day in the field or an afternoon in the museum might be given as a reward for diligence and proficiency in other departments, and in this way a certain amount of available information might be imparted without any attempt at formal instruction.—Page's "Geology as a Brunch of General Education."