XXXV. The maximum difference, at a given period, between two or more languages is also capable of being approximated.

XXXVI. The original unity of the species is a postulate. XXXVII. The minimum amount of time necessary for the maximum amount of difference is the measure of the shortest admissible recent period.

XXXVIII. The probable nature of the future changes in the relationship between the different varieties of man is, certainly, within the department of the ethnologist. In this case, however, he reverses his method, and arguing from the past and present to the future, argues from cause to effect also.

XXXIX. Still his proper sphere is limited to the appreciation of physical influences. The historian measures the influence of a great warrior. The ethnologist inquires whether the American of New England can be acclimatized to the intertropical influences of Brazil.—Latham's Natural History of Man, p. 559.

On the Connection between the Colour and the Magnetic Properties of Bodies. By RICHARD ADIE, Esq., Liverpool. Communicated by the Author.

In continuing my experiments* on the connection between the colour of bodies and their magnetism, I was desirous, in the first place, to determine the nature of several substances which contained particles that moved on a sheet of paper to a magnet underneath; for, in applying this test, such bodies had appeared much more numerous than I expected, and as I had been cautioned against the prevalence of iron, which by treatment may become unmasked magnetically, I took care to prepare the salts free from this metal, and to test for iron in every stage of the operations. Notwithstanding these precautions, I found in the repetition of the experiments metallic particles containing carbon to move on a sheet of paper to a magnet underneath; in every case such bodies forming only a small proportion of the pulverulent mass, made me apprehensive that there was yet some other impurity, rather than to suppose that this was the true magnetism of those particles; an opinion that was soon confirmed. For, on substituting a sheet of silver foil for the paper, I found

* See Vol. 50, p. 214, of this Journal.

that the electrified state of the dry paper surface had much influence in producing these movements, and that when this was guarded against, the number of bodies furnishing particles to be moved on silver by a magnet underneath, became much reduced. With the silver cold, they were confined to the numerous compounds of the three magnetic metals, iron, nickel, and cobalt; but when the silver was heated, the number of such bodies began to increase. In the experiments in my first communication, where I used the magnet under a sheet of dry paper, the white and dark coloured products were tried under similar conditions; so that although the magnetic effect was mixed up with an electrical action, the results are not thereby invalidated; and at the time I kept checking them continually, by submitting each substance in its dark and light coloured state to a comparative trial on the torsion balance, where the dark coloured one shewed most magnetic attraction. But in writing out an account of these experiments, I preferred, wherever I could, to give the paper test, as it appeared to me to be a more palpable proof than the other, and to admit of more easy repetition.

To continue the evidence that shews that magnetic bodies form a larger proportion of dark coloured compounds than diamagnetic ones, I selected from Dr Turner's chemistry a list of the oxides of the elementary bodies I had examined for their magnetism on the torsion balance, which supply the following numbers :

In classifying these oxides I have referred to the anhydrous form, excepting in a few cases where this has not been insulated, for there the hydrated oxide is classified. From Gmelin's chemistry I selected the compounds of metals arranged in three different groupsthe first magnetic metals; the second, metals of feeble magnetism in

Iron,. Nickel, Cobalt,

themselves, but magnetic in many of their compounds; and the third, diamagnetic metals. In reading over the descriptions of nearly 1500 combinations for this purpose, some, the majority of which are probably colourless, had to be omitted for the want of an explicit statement about colour; but by pursuing a uniform principle in the classification of all, the results, it is hoped, are nearly the same as would be obtained by the more rigorous method of examining in the hand each substance before classifying it.

Το compare these numbers together in order to shew the relative proportion the transparent or white bodies bear to the coloured in each class, a common integer is found to convert the former into 100, thus-for every

100 White Oxides of Magnetic Bodies, there are 336 Coloured.

Diamagnetic,

Compounds of the 3 Magnetic Metals,

47

400

259

63

Giving proportions which do not materially differ from those I had previously derived from the tables of the colours of the precipitates by the re-agents used in testing, but being founded on the descriptions of a much larger number of combinations, are more satisfactory as evidence of the general tendency of magnetic bodies to form coloured combinations; the difference between these and the diamagnetic, as derived from Gmelin, being as 400 to 63.

Carbon, Nitrogen, and Hydrogen.-These elementary bodies in their combinations with one another, give compounds which, on the torsion balance, shew very clearly the influence of colour on magnetic properties. Carbon and hydrogen form turpentine and naphtha, colourless diamagnetic fluids. Carbon and nitrogen form cyanogen, a colourless gas, strongly diamagnetic, according to Faraday; they

Transparent

or White.

Coloured.

also produce para-cyanogen, and proto-carburet of nitrogen, two substances of a dark colour, which, on the torsion balance, are feebly attracted by the magnet.

Corolla of Flowers-The result of the trial of a number of different corollæ on the torsion balance before a magnet, was, that the white colours were, when fresh, diamagnetic, while the coloured corollæ varied much, the diamagnetism of many being apparently due to their moisture, which, at the same time, tends to make them transparent; moreover, I observed that change of season and of the site of the flowering plant frequently had an influence. From these experiments I may select one or two which serve to shew the connection of colour with magnetic properties. Two cineraria flowers were tried, the one white, tipped with crimson, the other a rich strong blue; the white was inert, while the blue was decidedly attracted. The corollæ of the pile-wort and dandelion were compared together, the first being attracted, the second repelled. The pilewort is an early spring flower, peculiar in its glistening surface, that gives it a varnished appearance. Our fruit shops in the winter season abound with dyed everlasting flowers imported from France, which contain colours that shew very well the change of magnetic properties, and being in a dried state, the results are not subject to that disturbance which the moisture of fresh flowers occasions; the pale yellow is diamagnetic, the dyed chrome-yellow nearly inert, the verdigris-green feebly magnetic, and the logwood-purple magnetic. I believe the effect of the sun's rays on the colours of plants has been noted; in the course of the above experiments I had to attend to the nature of these changes. Solar rays bleach dead vegetable matter with rapidity, while in living parts of plants their action is frequently to strengthen the colour; two opposite effects, which, according to my experiments, should be accompanied by different magnetic properties. The bleaching power of the sun's rays is familiar to every one; their power in developing fine colours is perhaps best seen on the sides of peaches, apricots, apples, &c., &c., in these the sides exposed to the midsummer sun being highly coloured. During the last open winter a wallflower plant afforded me the proof of a like effect; in the dark months there was a slow succession of one or two flowers, to give it the appearance of flowering all the winter; these were of a uniform pale yellow hue; in March streaks of a darker colour appeared on the flowers, and continued slowly to increase, till, in April, they were variegated brown and yellow, of rich strong colours. On the supposition that these changes are accompanied by alterations of magnetic properties, we may hereafter be able to explain Mrs Sommerville's experiments on steel needles exposed to the sun's rays under envelopes of silks of various colours. The results obtained by that distinguished lady have been the source of much discussion among men of science; and there can be no doubt that the most rigid experiments have failed to magnetize steel needles in the coloured rays

of the spectrum. But to magnetize them under envelopes of dyed silk is quite a different experiment, and if I do not much mistake, the effect in this case will hinge on the chemical change wrought in the silk and its dye by the solar rays; consequently, to repeat the experiments hereafter, it will be necessary to attend to the materials used in the dyeing.

In concluding this inquiry I may repeat, that I view the nature of the connection between colour and magnetism to be, that there are forces which act in common on the magnetism and the power of the body in transmitting or reflecting light. Faraday and Plucker have previously shewn the intimate connection between the crystalline and the magnetic force; while the tendency of my experiments has been to shew that the colour, a property much more strongly attached to a body than its crystalline force, is likewise connected with the magnetism. When a number of bodies are grouped together the connection is seen clearly enough; but when single cases only are examined, apparent contradictions are not unfrequent. This appears to me to indicate that colour and magnetism are mixed up with other qualities derived from the forces of aggregation, together giving the varied properties possessed by the bodies by which we are on every side surrounded, while the further knowledge for the unfolding of these may demand the labour of countless ages to come.

A Comparative Examination of the Objective Glasses of Microscopes, from Mr Ross of London, Mr Spencer of America, and M. Nachez of Paris. By J. LAWRENCE SMITH, Esq. Having had an opportunity a short time since, while at Paris, to examine the comparative merit of the lenses of these makers, it might not be uninteresting to microscopists to know the result of my examination, particularly as it was made under peculiar circumstances-namely, by adapting alternately the objectives to the same mounting, and regarding the same object under the same illumination.

The glasses used were considered by their makers as among their best. That made by Ross was in the possession of M. Rutherford of U. S. Spencer's was owned by Dr Burnet of Boston, and had just been brought by him from Spencer That of Nachez belonged to Dr Bigelow of Boston, now in Europe, engaged in microscopic research very creditable to himself. Their magnifying powers varied from thirteen