spectra of very minute crystals, of very small quantities of material in solution, and of small blowpipe beads. As previously named, the thickness of the object makes a very great difference in the spectrum. For example, an extremely thin crystal of ferrideyanide of potassium cuts off all the blue rays, and leaves merely red, orange, yellow, and more or less green; but on increasing the thickness, the green and yellow disappear; and when very much thicker, little else but bright red light is transmitted. In all such cases, the apparent magnitude of the effect of an increase in thickness is far greater when the object is thin than when thick, and past a certain thickness the change is comparatively very

ing article on this subject to the Popular Science Review, from which we make the following extracts:

"Every one is in the constant habit of distinguishing different objects by their colour. In many cases this is sufficient to characterize various small bodies seen with the microscope. Now, strictly speaking, spectrum analysis is nothing more than a refined and scientific method of applying the same principle, and the spectrum microscope is simply an instrument which enables us to employ it in the case of very small objects. It is a more refined method, because we may have a number of different substances so nearly of the same colour, that it would not enable us to tell one from another; and yet, when examined with a spectroscope, their spectra might be entirely different and quite characteristic. On the contrary, we may have cases where the presence of foreign colouring matter so entirely disguises the natural colour of a substance, that its presence would scarcely be expected: and yet, when examined with a spectroscope, the spectrum may be so characteristic, that its presence is perfectly well established. In these remarks I refer to coloured solids or liquids. The spectroscope has been so commonly restricted to the examination of coloured flames-i.e. to the study of the light given off from incandescent vapours that I have found many persons who believed, that in order to obtain the spectrum of such substances as blood it is requisite to burn it. There can be no doubt whatever that, on the whole, the facts to be learned from the study of mineral matter in the state of incandescent vapour are far more important and decided, because the spectra are far more characteristic; but still we may learn a number of valuable facts in studying the light transmitted or reflected from solid or liquid coloured substances."

well to mount a number of different thickness; but when it is possible to obtain crystals of sufficient size, it is far better to make them into wedge-shaped objects, since then the effect of gradual change in thickness can casily be observed. Different kinds of crystals require different treatment, but, as a general rule, I find that it is best to grind them on moderately soft Water-of-Ayr stone with a small quantity of water, which soon becomes a saturated solution, and then to polish them with a little rouge spread on paper laid over a flat surface; or else, in some cases, to dissolve off a thin layer by carefully rubbing the crystal on moist blotting-paper until the scratches are removed. Then, whenever it is admissible, I mount the crystal on a glass, and also cover it with a piece of thin glass with Canada balsam. Strongly coloured solutions may be examined in test-tubes, or may be kept sealed up in small bottles made out of glass tubes, the light then examined being that which passes through the centre of the tube from side to side. Such tubes may be laid on the ordinary stage, or held on the stage attached to the eye-piece. Smaller quantities may be examined in cells cut out of thick glass tubes, one side being fixed on the ordinary glass with Canada balsam, like a microscopic object, and the other covered with thin glass, which readily holds on by capillary attraction, or may be cemented fast with gold size or Canada balsam, if it be desirable to keep it as a permanent object. Such tubes may be made of any length that may be required for very slightlycoloured solutions. Cells made out of spirit thermometer tubes, so as to be about one-tenth of an inch in diameter, and half an inch long, are very suitable for the examination of very small quantities; but where plenty of material can be obtained, it is far better to use cells cut out of strong tube, having an interior diameter of about three-fourths of an inch, cut wedge-shape, so that the thickness of the solution may be one-fourth of an inch, or more, on one side, and not above one-fortieth on the other; and then the effect of different thicknesses can easily be ascertained."

We can only quote one other paragraph, which

"For

relates to the detection of blood-stains. tunately, the various modifications of the colouring matter of blood yield such well-marked and characteristic spectra, that there are few subjects to which the spectrum microscope can be applied with greater advantage than the detection of blood-stains. I have already, in my paper in the Quarterly Journal of Science (April, 1865, II. 205), entered at so great length into this question, that I need not say much about it on the present occasion. The form of apparatus I have described enables us, however, to examine the objects in a different manner: surface illumination may be used, provided a sufficiently bright light be thrown on the object by means of a parabolic reflector or bull's-eye condenser. A speck of blood on white paper shows the spectrum very well, provided it be fresh, and the colour be neither too dark nor too light, and the thickness of the colouring matter neither too great nor too little. A mere atom, invisible to the naked eye, which would not weigh above the millionth of a grain, is then sufficient to show the characteristic absorption bands. They are, however, far better seen in solution. About of a grain of liquid blood, in a cell of of an inch in diameter, and inch long, gives a spectrum as well marked as could be desired. In exhibiting the instrument to a number of persons at a mecting, I have found that no object is more convenient, or excites more attention, than one in which a number of cells are fixed in a line, side by side, containing a solution of various red-colouring matters. In one I mount blood, which gives two well-marked absorption bands in the green; in another magenta, which gives only one distinct band in the green; and in another I place the juice of some red-coloured fruit, which shows no welldefined absorption band. Keeping a larger cell containing blood on the stage attached to the eye-piece, these three objects can be passed one after another in front of the object-glass, and the total difference between the spectrum of blood and that of either fruit-juice or magenta, and the perfect identity of the spectra when both are blood, can be seen at a glance. By holding coloured glasses, which cut off the red, but allow the green rays to pass, we can readily show how the presence of any foreign colouring matter, which entirely alters the general colour, might not in any degree disguise the characteristic part of the spectrum; and by changing the cell held

a

solution of cochineal, it is easy to show that, though it yields a spectrum with two absorption bands, more like those due to blood than I have seen in any other substance, they differ so much in relation, size, and position, that there is no chance of their being confounded when compared together side by side." Any of our readers specially interested in the subject are recommended to peruse the article from which the above extracts have been made.

FEW people are aware of the beauty to be found

in many members of the Grass family. Even our agricultural grasses are very ornamental when properly dried and arranged. I believe about a hundred and sixteen species of grasses are found in Great Britain, and from this number I shall select a few of the most desirable, leaving what are called the "Ornamental grasses " for another gossip.

I would first state that in order to preserve grasses for winter bouquets it is requisite to cut them when they are just coming into flower, before any seeds are formed, when the pollen first becomes visible, and dry them by sticking the stems into boxes of sand.

The Meadow Bucetum or Fescue, which has puzzled botanists a good deal in determining its character, presents a very graceful, wavy appearance. It is generally found in meadow ground, and flowers about the middle of June. The rough-stalk Meadowgrass, better known, perhaps, as the famous Orchistore grass, from being found of extraordinary size in a meadow near Salisbury, called Orchistore, is also very pretty. Its flowers may be looked for about the second week in June in well-irrigated land. The Fiorin grass, which some farmers anathematize as a weed, is another elegant addition to the dried bouquet; and the crested Dog's-tail, known in Ireland by the name of Trahneen, looks remarkably well; its flowering stems are very wiry, and often used in the manufacture of imitation Leghorn bonnets. The sweet Vernal grass, the only British grass that is odoriferous, so like in scent to that charming little plant the wood-ruff, blossoms early in May, and is to be met with in thickets and on poor up-land pastures. Then we have the perennial Rycgrass, which village girls are so fond of trying their fortunes with, to the measure of "Tinker, tailor, soldier, sailor, &c.;" and the rough Cock's foot grass, found so common in Norfolk. The Fox-tail, which only occurs in deep, rich, moist, and sheltered ground; together with the Cat's-tail, found on clayey soil; and last, though not least, the Sea-lime grass, which, I believe, is rather rare except on chalky soil. It

blue colour, and decidedly worthy of being classed among our most ornamental grasses. Ferns have been the rage for some time, even the most common kinds of British; and mosses, too, have their admirers why should we not have a grassery, or mix some of our native grasses with our ferns? I believe the effect would be better than when grown in a formal way by themselves.

H. E. WATNEY.

ON SOME PESTS AND THEIR CHECKS.

THERE is a subtle relation between the health

of plants and the attacks they suffer from insects. One may watch an apparently healthy, vigorous shoot on a favourite rose-bush and expect it to be presently crowned with roses. Has a current of cold air breathed unkindly upon it? Has an Aphis in its perfectly-developed winged state halted there a moment, and unseen deposited some eggs?

Quien sabe (who knows) ?-but there comes first an uncomfortable roughness, as if the plant were perspiring through the pores of its epidermis. These small beads of moisture soon show themselves to be living six-legged creatures, with bodies of bright green jelly, and they grow and increase, both in size and numbers, with the most marvellous rapidity, till they jostle and tumble over each other, coating the stem and leaves with their bodies, as thickly piled together as a swarm of bees round the branch where their queen has settled. Alas! poor plant, how your life-juices will now be sucked and drained! But help is at hand when least expected. Gardeners in general do not like ants: they accuse them of disturbing the soil from the roots of plants, and of various mischief. Yet now they come as allies to help the beleaguered fortress. In serried file they issue from their citadel, march in straight line across gravelpaths or smooth-raked border, climb up the stem, and quickly settle themselves where the Aphides are thickest and busiest, and greedily drink the honey-dew which they excrete. There have been various meanings given to the oft-quoted remark of M. P. Huber, the younger, that "the plant-lice serve instead of cows and goats to the ants "-pastured through the winter they could not be; and Gould, Latreille, and others have found that the ants become dormant, and do not require stored-up food for that time. In this little episode of the raid of the emmets on the rose-bush, there could be no such commissariat-providing prevision as that by which the respectable Dr. Watts would have us think they foresee all the frosts and the storms, and so bring their food within doors;" on the contrary, judging by the dried, empty skins, and the altogether defeated and discomfited state of the Aphides, one may suspect that the ants, God Bacchus -like, mounted on and tapped their barrels of liquor, and gorged themselves with the sweet incbriating juice fresh from the heart of the distillery, till heavy and stupefied, the ants roll helplessly on the stem, and possibly, by the formic acid exuding from them, might do more harm to the plant than their soft green predecessors. But help comes again: amongst the dark mass of the now lazy ants, move some red coral beads prettily speckled with black; these are Coccinella, equally greedy after the Aphides and the honey-dew, they soon dislodge those who would

debar them from their feast, and the ants helplessly tumble about and nearly disappear, as the Aphides. had done before. Ah, then, "lady-birds, lady-birds, fly away home," stretch out your pretty gauze winglets-begone; shelter yourselves in the dahlias or under the broad sycamore leaves, and lick up what remnants of honey-dew you can find, for here come numerous feathered flutterers to pick you up like grains of wheat. Your friends the hop-growers will willingly help to hide and protect you for the sake of the great services you render them against the Hop-aphis. In confirmation of my suspicions against the sobriety of the ants, Dr. J. E. Gray has just written to me, "I know that ants do get drunk." They pass up the stem of the laurel, the broad-leaved evergreen (Prunus Laurus-cerasus), drink the secretion from the gland on the petiole, and get so mugged they cannot find their way down again, and some seem to die on the spot.

Dr. Kirk told me he caught the Galagos (a small Lemur) when they had been up in the palm-trees drinking the juice which the negroes brew into palmwine, and they would come staggering into the house, and were easily caught. On mentioning this to a friend, a distiller, he told me he had a Skye terrier given to him which got the habit of going to the end of the worm and sipping the spirit as it dropped out, and got so intoxicated it could not walk, and nothing could cure it, so it was obliged to be sent away where spirits were not made. The Aphides we have spoken of have soft green luscious-looking bodies, which offer an easy and tempting prey to their enemies; others have curious means of defence. For instance, the little green insect which involves itself in a wet frothy spume, and either from its making its appearance when the cuckoo calls, or because it is more frequently found on the cuckoo-flowers (Cardamine pratensis) than on any other plant, has the popular name of Cuckoo-spit.

The Aphis lanigera, commonly called American blight, which so deforms our apple-trees with great white scabs, is rolled in webs of cotton-wool, which not only preserve the inclosed insects, but serve them as flying chariots; small flakes of the web being wafted by the wind from tree to tree spread the pest. If you take hold of these flakes, your fingers become bloody with the insects, whose covering you thus crush. This sort was particularly abundant in this last hot, dry summer; but after the heavy autumn rains the apple-trees appeared to be washed quite clean, and the woolly patches had disappeared. On searching closely in November, however, I found in cracks, in the axils of branches here and there, a very small soft grub inclosed in a smooth silky cocoon, which, I think, was the chrysalis state of the perfect Aphis; and which, in spring, would produce the wool-spinning stage of the Aphis. In the cocoon state, however, they are accessible to the bills of such small birds as may be industrious enough to

seek them out. Let us hope the Black-cap, or some of his relations, may make many a feast on them, and by thus clearing the trees give us fair reason to sing the olden charm said to have been formerly constantly practised in the great orchard districts, such as I saw this autumn in many of our southwestern counties glowing with loads of richer and ruddier gold than the fabled gardens of the Hesperides. On the eve of Twelfth-night, it was the custom for the farmer and his work-people to go out into the orchard after supper with a large milk-pan full of cider, having roasted apples pressed into it, Out of this each person in company took an earthenware cup full of liquor; and, standing under each of the most fruitful of the apple-trees, addressed it thus:

Health to thee, good apple-tree,
Well to bear pockets full, hats full,
Pecks full, bushel-bags full-

and then, drinking part of the contents, threw the
rest, with the remnants of the roasted apples, at the
tree, and at each cup the company set up a great
shout. There are many curious old customs and
legends about the apple-tree recorded in Hone's
"Everyday Book."
P. S. B.

THE SCALES OF INSECTS.

more apt illustration could be given of the truth of the proverb, "All is not gold that glitters," than these minute structures. The illusion in many cases is complete: the scales of the various sorts of Diamond Beetle, for instance, resemble the polished surface of the precious metal so closely, that no description, without reference to gold and jewels, can convey an idea of the splendour which enwraps many of them; and it requires an effort to certify the mind that the brilliant reflections are, in reality, not metallic.

Many observers have vainly endeavoured to satisfy themselves as to the precise cause of the phenomenon. Theories have been put forward on the subject, but we are yet in ignorance why certain scales, presenting under transmitted light a uniform semi-transparent appearance, and similar markings, should, under reflected light, differ widely from each other-some reflecting green, others blue, others red, and others again yellow. Even in the same scale great contrasts are observable.

It is to be noticed, that in all cases, when colour appears to be really present, the scales are to a great degree opaque when viewed by transmitted light. This is especially the case with those more deeply coloured, such as brown, black, and dark red.

Another point is, that a great similarity obtains in the tracery of these opaque scales of lepidoptera, which may be well observed in those coloured light red, yellow, and white, even although they vary in outline, and be procured from different insects. The

darker scales cannot be examined with so much facility.

In the earlier days of microscopical inquiry, certain selections from these objects were used to test the glasses of high magnifying power; but such great progress has been made in this manufacture, that nowadays their employment for this purpose is almost abandoned. Nevertheless, some of them still decline to reveal their beauties, except through the medium of the most exquisite specimens of the optician's skill.

The intention in this chapter is, to bring forward such examples for special description as are notable for their departure from the general type, or are interesting to the microscopist for various reasons, beauty in particular.

the wing may be found green and blue scales vying with each other in lustre, yet they are identical in appearance when transmitted light is used in their

The Meadow Brown Butterfly (Hipparchia Janira) furnishes a test of considerable difficulty. The outline resembles the scale from Pieris Brassica, but the markings are much finer.

The battledore scales from the Azure-blue Butterfly (Polyommatus) have always been favourites, owing to their unique shape and peculiar surface markings. Being very minute, considerable magnifying power must be employed.

The scale of the Gnat (Culex pipiens) is also very curious; the longitudinal striæ look more like the folds in a lady's fan than anything else.

Figs. 56, 57. Scales of Pieris Brassica x 450. examination. Under these circumstances they appear of a light-brown colour.

The scales of the Morpho Menelaus, a splendid insect, measuring some 3 inches across the wings,

which are of the deepest skyblue colour on the upper surface, differ considerably from those of the Paris Butterfly. Formerly they were considered a severe test for an objective.

From the wing of the male of the Cabbage Butterfly (Pieris Brassica) are obtained two descriptions of scales; one somewhat resembles those from the Morpho Menelaus, but the other

Fig. 60. Scale of Ghat (Culex pipiens) x 450.

Fig. 61. Scale of Lepisma saccha

rina x 450.

The Lepisma saccharina, a little spindle-shaped creature of a dull leaden hue, with three filaments or bristles pointing outwards at the tail, inhabiting the old decayed woodwork of houses, is covered with very beautiful scales.

The name implies the connection of the creature with sugar-casks. I used to be able to procure a specimen whenever I wanted from the kitchen hearth, which was somewhat out of repair; but

Fig. 58. Scale of Hipparchia Janira x 450.

Fig. 59. Battledore Scale of Polyommatus Alexis x 450. is altogether different, and requires a good quarter to exhibit the markings satisfactorily; indeed, neither of the two is easy of resolution.

Fig. 62. Scales of Sea-side Lepisma x 450. since it has been mended I have not caught one. Perhaps they were out on foraging expeditions among the bits dropped near the fire-place, and the