would have been more proper to have signified such serial homology by giving the general term applicable to such parts, as abstract vertebral elements.

The fact is, however, that the mastoid (s) is the parapophysis of its vertebra, whilst the ilium is a portion of the pleurapophysis of its vertebra; and the mastoid is serially homologous with the transverse process (parapophysis) of a sacral vertebra (fig. 27, p), not with the pleurapophysis or ilium'; it is not, therefore, a repetition of the ilium in the skull. The true expression of the ideas which suggested the terms ilium of the head,' 'scapula of the head,' &c., will be found in the true enunciation of the serial homologies of the vertebrate skeleton.

It finally remains for inquiry, admitting the explanation of the endoskeletal archetype given in this Report to be the true one, whether such is the ultimate attainable generalization, or whether we may not also gain an insight into the nature of the force by which all the modifications of the vertebrate skeleton, even those subservient to the majesty of man himself, are still subordinated to a common type.

We perceive in the fact of the endoskeleton consisting of a succession of segments similarly composed,-in the very power, in short, of enunciating special, general and serial homologies,-an illustration of that law of vegetative or irrelative repetition which is so much more conspicuously manifested by the segments of the exoskeleton of the invertebrata, as, for example, in the rings of the centipede and worm, and in the more multiplied parts of the skeletons of the echinoderms.

The repetition of similar segments in a vertebral column, and of similar elements in a vertebral segment, is analogous to the repetition of similar crystals as the result of polarizing force in the growth of an inorganic body.

Not only does the principle of vegetative repetition prevail more and more as we descend in the scale of animal life, but the forms of the repeated parts of the skeleton approach more and more to geometrical figures; as we see, for example, in the external skeletons of the echini and star-fishes: nay, the calcifying salt actually assumes in such low-organized skeletons the very crystalline figures which characterize it when deposited, and subject to the general polarizing force, out of the organized body. Here, therefore, we have direct proof of the concurrence of such general and all-pervading polarizing force with the adaptive or special organizing force in the development of an animal body.

The marvellous phænomena of this development have, hitherto, been explained by two hypotheses or forms of expression, as the result, viz. of vital properties' either peculiar to living matter or common to all, but latent in dead, matter; or, as due to the operation of one or more 'vital principles,' vital forces, dynamies or faculties, answering to the idea of Plato, deemed by that philosopher to be superadded to matter and mind, and which he defined as a sort of models, or moulds in which matter is cast, and which regularly produce the same number and diversity of species*.

Now besides the idéa, organizing principle, vital property, or force, which produces the diversity of form belonging to living bodies of the same materials, which diversity cannot be explained by any known properties of matter, there appears also to be in counter-operation during the building up of such bodies the polarizing force pervading all space, and to the operation of which force, or mode of force, the similarity of forms, the repetition of parts, the signs of the unity of organization may be mainly ascribed.

The platonic icéa or specific organizing principle or force would seem to *See Barclay, Life and Organization, 8vo, 1822.

be in antagonism with the general polarizing force, and to subdue and mould it in subserviency to the exigences of the resulting specific form.

The extent to which the operation of the polarizing or vegetative-repetition-force is so subdued in the organization of a specific animal form becomes the index of the grade of such species, and is directly as its ascent in the scale of being. The lineaments of the common archetype are obscured in the same degree but even in man, where the specific organizing force has exerted its highest power in controlling the tendency to type and in modifying each part in adaptive subserviency to, or combination of power with, another part, the extent to which the vegetative repetition of segments and the archetypal features are traceable indicates the degree in which the general polarizing force may have operated in the arrangement of the parts of the developing frame and it is not without interest or devoid of significance that such evidence should be mainly manifested in the system of organs in whose tissue the inorganic earthy salts most predominate.

On Anemometry. By JOHN PHILLIPS, F.R.S., F.G.S.

ANEMOMETRY, or the registration of wind, is a process of recording certain effects of the (horizontal) pressure or movement of the atmosphere. According to the kind of effect which is subjected to observation, and to the process of measuring, weighing or counting which is adopted, the anemometrical instruments vary, and it is required to determine the forms of these instruments which are best adapted for accurate meteorological inquiries. Correct anemometers may be applied with advantage as auxiliaries in a variety of important problems not meteorological, but they are of primary importance in meteorology, and derive their value in other branches of knowledge from their proved adaptation to this.

A complete anemometrical register should give on a scale of time the direction of the wind, and its pressure or velocity in a continuous series, or at very frequent intervals, for days, weeks, months or years. We may for particular inquiries be desirous of learning the total space traversed by the aërial movement, or be satisfied with knowing the maxima and minima of pressure, in a given period of time, or in other ways simplify the problem, which in its general form cannot be solved without adding a clock or other register of time to the apparatus for measuring wind.

Mechanical Effects of the Movement of the Atmosphere.

The (horizontal) movement of the air over any given point on the earth's surface, one of the most important desiderata in meteorology, can only be observed directly in the phænomena of the clouds. The velocity of these light bodies may be measured trigonometrically, by their change of position, or when the sun shines, by observing the progress of their shadows on the ground. But these are rather experiments than observations, and when we attempt by instrumental means to register the velocity of the wind, some considerable difficulties at once appear. The air moves because it is pressed: machines to be influenced by wind must be made to receive and yield to its pressure. If this pressure be received on a machine so contrived that it has a resisting power, which rises with the increase of pressure till equilibrium is gained, the displacement of the spring, the elongation of the lever, the augmentation of the weight, &c. may be taken as proportioned to the

PRESSURE. Many such instruments have been invented, the most famous being M. Osler's anemometer, first erected at Birmingham.

But if the pressure (P) be received on an instrumental contrivance, which (its inertia being overcome) is set into a continuous motion (as the various sorts of windmills), the rate of this motion goes on increasing till the resistance which the motion generates balances the wind-pressure on the sails. This resistance consists of two parts, one caused by the displacement of the air in the path of revolution of the sails, and consequently proportioned to the square of the velocity of revolution (or to v'); the other caused by the ordinary friction of machinery, which being a uniformly retarding force (b), destroys the power P exerted on the machine a quantity proportioned to the space moved over*, and consequently to v'. P then is prop. to a v'bv', the coefficients a and b requiring to be separately determined for each instrument.

If we conceive friction to be very small, so that the second term almost vanishes, the velocity of revolution becomes nearly proportioned to V, the velocity of the wind; but if friction be very large, the velocity of revolution of the machine becomes nearly proportioned to P or V2. The former is the case on a windmill in heavy wind-pressures; the latter of the same machine when the wind-pressure is light t.

Hence all machines of this kind have a rate of revolution proportional to the movement of the air, retarded by quantities which are proportioned to something else. The smaller we can make this retardation, the nearer to perfection is the instrument. Such an instrument is Whewell's anemometer.

Whewell's Anemometer.—Assuming in respect of this instrument that its general action is like that of a windmill, we see with low velocities of wind, the term b v' is not only greater in proportion to a v'e than with high velocities, but may acquire a higher numerical value than it.

Coulomb found with a windmill (the load being constant), the following proportions of wind's velocity and revolutions of sail :

Wind Vel. Revolutions.

:

We

may with these data compare the following calculation :

*This is not strictly the case with varying pressures of wind, if these act unequally on the bearings of the axles.

+ Mr. Harris's experiments with Whewell's anemometer (Reports of the British Association, 1844, p. 245) confirm this view. He had previously observed (Reports of the Association, 1842, p. 33) in one limited set of experiments with low velocities of wind, the space described by the pencil to be proportional to the square of the velocity of the wind. But in a larger series of trials, in strong and steady breezes, the spaces passed over by the pencil came nearer the simple ratio of the wind's velocity. In strong winds the ratio between the revolutions of the fly and the velocity of the wind is [nearly] constant.

In this calculation a is taken at 10 and b at 14-75. The small differences are quite within the range of errors of observation.

Mr. Harris has furnished us with experiments* in which the revolutions of the vane of Whewell's anemometer were compared directly with the wind-pressure on Lind's well-known instrument, and to these the same form of calculation is equally applicable. In the subjoined Table the observed values of v' and V2 are first given, and then a column of values of V2, calculated from the formula Pav'2+ bv', the values of a and b being taken at 1 and 10.

By this very simple calculation, then, any one rate of revolution of the vanes of Whewell's anemometer may be made to indicate the corresponding velocity of the wind. But we cannot from the sum of these rates, obtain by this calculation the corresponding sum of the velocities of the wind; since the relation of these sums to each other depends on the individual values of v', and these are not recorded. They may be recorded, in a form fit for the calculation, by adding a clock-movement, which shall cause the instrument to register the series of values of v', but the machine then loses its simplicity. An approximation to the individual values of ' may be had by a process suggested by the inventor, but not (it is believed) put into constant use by any observer. It consists in simply turning round the cylinder, on which the wind register is written, after regular intervals of time by hand. The shorter these intervals, the nearer the approximation.

If we knew precisely the law according to which the wind's velocity rises and falls with the lapse of time, the correction of the record in Whewell's anemometer might become more complete; and it seems no small recommendation to observers for practising the hourly rotation of the instrument, that this process would speedily furnish data for the determination of that law.

The conversion of the register effected by Whewell's anemometer into pounds of pressure or miles of air-movement may perhaps be sufficiently easy and accurate, if only two things are attended to:-first, the values of the constants a and b in the previous formula must be determined by observation; and secondly, the register scale should be read and the results recorded sufficiently often to obtain an adequate number of values of v'.

* Reports of the British Association, 1844, p. 263.

+ The observation must be a comparison of Whewell's registration with some experimental contemporaneous determination; the simple pressure of wind may be obtained by Lind's