for a succession of mornings and would number many repetitions in the course of every winter. The writer counted a dozen fine exhibitions of this kind before one winter was half gone. In cold weather, a perceptible thin vapor comes on at night, not uncommonly, when the air has a stillness favorable to the growth of this icy leafage. In certain covered situations, where moisture rises, cobwebs are changed to a lace-work of crystals, the length and delicacy of which would be incredible to one who never lived in such a climate. In a cellar stair way, the plastering and shelf and every article on it were soon robed with a polar-bear fur of icy filaments, so long that the smaller articles lost their identity of shape.

It is well known that the fine porous soil of the West has a marvellous ability to support vegetation, during the long droughts that characterize the region. The cracking of the earth in a prolonged drought is wonderful, especially along the beaten surface of roads. Fissures over an inch across have been measured. How the subsoil can retain any moisture, with such openings down into its heart, is a mystery. On the high treeless rolling prairie, however, at the summit level between river systems, water is readily obtained at a depth of from fifteen to twenty feet, though not always in suflicient quantity. The manner in which wells are made for the supply of mills, in such a situation, is worthy of publication. A shaft is sunk, say thirty feet, and from the bottom galleries are drifted in various directions, in the style of a mine, sometimes to the length of a hundred feet. Thus, numerous very small veins are struck, which, all together, give a large supply of water. The workmen report these veins as occurring at somewhat regular intervals, and as indicated by a root-like mass of darker earth; it is affirmed, too, that they follow one general direction,-in one instance at least, said to be transverse to the surface drainage.

In this connection, reference may be made to the subterranean cryptogams that penetrate almost every inch of the deep, loamy gray clay beneath the top soil in that prairie region, and perhaps in all similar districts. This vegetation, threadlike or coarse stringlike, is coated with dark discolored earth, and is mostly dead, the thread lying shrivelled, black and loose in its cylindrical cavity; but the writer has found the filaments apparently fresh and living at a great depth—even to the depth of eight feet, if his memory is not at fault.

One very common peculiarity of the surface drainage may be

noticed

the extent to which the water of the sloughs, or swales, reaches up the acclivities on either hand, even where the interval has a very considerable descent in the line of flow; there is thus a broad concave bog that must strike a stranger with surprise, for it is not due to springs, but rather to a spongy retention of rainfall. Some peculiarities of prairie storms should not be omitted in this sketch. Nothing at the West is done by halves; when it rains, it rains; and the general surface is so uniform, the soil to a certain depth so pervious, that something like a subterranean lake is suddenly formed, which rapidly rises, flooding cellars and even bursting up the cement of cellar floors by hydrostatic pressure, if cement has been resorted to, by the trustful immigrant.

One species of prairie storm should be elevated to the rank of a genus. It is mostly nocturnal in its habits and prowls all night; its distinguishing characters are surges of rain, rhythmic roar of wind like that of heavy billows on a coast, incessant quiver of lightning, and overlapping continuous peals of thunder. It is as if the spirits of the old American Mediterranean sea were claiming again their last battle-ground—a suggestion harmonizing with the ocean-like level of the country and the looming mirages of sunny days. But the lightning of this species of storm seems to be among the clouds, and the new-comer soon becomes fearless; indeed, it does not require a long residence at the West to make one familiar with lightning, however timid he may have been at the East, although it remains true that thunder gusts are not pleasant to a person who is out on the open prairie, where man or horse is the only prominent object to attract the downward or upward bolts of electricity. Finally there is something peculiarly grand in western thunder. No hills break its smooth roll, and its long crescendos and diminuendos give a breath and cadence to the sound, as if chariots could be heard rolling on for hundreds of miles over the level prairie floors.

The subjects of this article have not been in the path of the writer's special study; but he believes that the prairie region offers a fresh and interesting field of observation in this regard. The reports and books where the information might properly be looked for, have failed to give him, any information in respect to the relative humidity of the prairie atmosphere-a matter of prime importance. On average winter days, the writer found it from forty to fifty hundredths of saturation.

REMARKS ON UNIFORMITY OF NOMENCLATURE

IN REGARD TO MICROSCOPICAL OBJEC

TIVES AND OCULARS.

BY R. H. WARD, M.D.'

THE nominal focal length of an achromatic objective, as used by microscopists generally, represents its amplifying power as actually used in the compound microscope. Even the equivalency in amplifying power with a single lens of the same focus is no longer distinctly realized, while the size and appearance of the combination, its working focus, angular aperture, and microscopical efficiency, are not even hinted by the figures used. The nominal focus represents the magnifying power and those properties dependent on it. Like other measurements, these must be stated by comparison with known standards. To use diverse and unknown units of measurement in cases designed to be compared with each other is simply self stultification. To call two lenses, of identical magnifying power, respectively one-fourth and onesixth inch lenses, is just as indefensible as to call two houses of equal height, forty and fifty feet high respectively. To argue against the existing looseness of usage in naming lenses, is only to state what everybody knows in regard to the advantages of uniform standards of measurement generally. So impressed are many microscopists with the urgency of this question, and so determined are they to escape from some of the present confusion, that a committee has been appointed to report on the subject. Though that com-* mittee is unprepared to report, it is believed that giving publicity to some facts and opinions involved in the consideration, may lead to useful agitation and to increased definiteness of ideas and of information in regard to it. Of course it would be premature to claim or expect accuracy of statement or safety of opinion in such a complication of disputed questions; and what is said, is designed to be contributory and suggestive, and in no degree dogmatic or final.

The great variation in objectives of identical name is familiarly

* Being the substance of remarks made by the writer at the Indianapolis meeting of the American Association for the Advancement of Science.

known and is undisputed. Among other people one-fourth of an inch is less than four-tenths and more than one-fifth; but among microscopists it may often be more than the first or less than the last. An indefinite number of figures might be published to prove or illustrate this irregularity, the writer having been particularly interested in making and recording these comparisons for more than a dozen years, and Messrs. Bicknell, Biscoe, Higgins, Cross, and many others having been especially interested in the same study; but it is idle to prove what everybody knows and admits. So familiar have some of these apparent errors become by use, and good usage too, that they have been often accepted as established, even one of the latest authorities* stating the power of the one-fourth-inch objective five times as high as that of the oneinch.

In the early days of the compound microscope as a really useful instrument, we find microscopists wishing that microscope makers would "grind their glasses to some settled standard." We are willing to be more reasonable now, or else the conditions stated have become more difficult. We do not desire, nor consider it practicable that the opticians should make all their combinations of certain definite and conveniently graded powers; but we do propose so to name our powers, if we can, that each number shall group together all those powers of which it is the nearest and best description.

Makers would doubtless be considered as doing a favor to those who use their instruments if they would. after finishing lenses, carefully estimate their powers and name them by the fractions most nearly representing those powers. But even if this were done, and much more now when this is certainly not done, or not done upon such a uniform plan as to be satisfactory, microscopists should always reëxamine their lenses in order to be definitely informed in regard to one of their most important properties.

The easiest method of examining the magnifying power of an objective, by measuring the image (of a known object) which it forms at a standard distance (now ten inches), was as well understood a hundred years ago as now; a lattice of fine silver wire or of human hair, or a scale ruled on glass, being used to measure

*Suffolk, Microscopical Manipulation, London, 1870.

† Baker on Microscopes. London. 1742.

the image. A positive ocular† or the eye-lens of a negative one is used as a simple microscope with which to read off the measurement. If a separate piece of apparatus were to be made for the purpose of measuring these powers, a positive ocular with micrometer attached would doubtless be preferred, it being placed by means of the drawtube or some other contrivance at such a height that its micrometer should be ten inches from the objective. Its reading would then give the real size of the image formed at that distance by the objective, and the ratio of this number to the known size of the object, say the distance apart of two lines on a stage micrometer, would give the magnifying power of the objective. But as few are possessed of a large variety of apparatus, or care to buy a piece for so infrequent a use as this, the measurement is generally made with an arrangement which every microscope ought to include, a negative ocular with a micrometer in the focus of its eye-lens, whose advantages for general micrometry are so well understood, giving the best view of the object and a sufficiently good view of the measuring lines, that it is usually preferred for that purpose. Of course the field lens is removed in measuring the power of the objective alone, but replaced for ordinary work. If it should be thought best to name lenses by their magnifying power alone, the power ascertained could be at once attached to the lens, the present one-inch lens becoming No. 10, or x 10:§ but if it should be the usage to name it by its power when combined with some standard (say two-inch) ocular, it would be marked No. 50, or x 50, or perhaps x 45 or x 55. Should it be preferred to retain the nomenclature by inches of focal length, a power of ten diameters might be called a one-inch lens, and powers above and below rated in proportion. This plan is within reach of the opportunities of every microscopist, while the plan of actually employing a single lens of small aperture and exactly one-inch focus as a standard of comparison is only adapted to the use of

* The measurement of the image, formed by the objective only, on a screen at a distance of several feet, as employed by Dr. J. J. Woodward at the Army Medical Museum at Washington, is unquestionably the most reliable method of determining the amplifying power; but is a method which requires too many applications and too much skill to be univer-ally applicable.

†The convenience and growing popularity in this country of this continental term suggest the propriety of its general substitution for the awkward name eye-piece. Dr. J. J. Higgins in the American Naturalist, Dec., 1870, p. 628.

§ It might be 9 or 11, and thus the various degrees of power would be conveniently expressed.