gular plates. We can say nothing, as yet, about the apertures or organs. The ambulacra have already been described. There is an obscure indication of a madreporic tubercle on one specimen near the apical junction of the ambulacra. From its general resemblance, and especially from the identity in structure and arrangement of the oral portion of the ambulacral system, I have little doubt that Palæodiscus is a flattened form of the family of which Echinocystites is the type; but a series of more complete specimens is necessary for the full elucidation of its structure and affinities. One Palæodiscus seems to have died adhering to a thin frond of seaweed, for, close to it, on the same lamina of schist, there are one or two circles of a small radiating polyzoon, very like a recent Lepralia, and round them a wide patch of the delicate chains of a Hippothoa, undistinguishable as internal casts from H. catenularia or H. Patagonica. The seaweed has not left even a stain upon the stone.

We have a fragment (Plate IV. fig. 8) of apparently another species too indistinct for full description. It is distinguished by its large, regular, lozenge-shaped inter-ambulacral plates; by the more distinctly petaloid form of the ambulacra; by the width of the inter-ambulacral avenues, and by the narrowness of the pore-bearing bands. The ambulacral double-pores are well marked.

EXPLANATION OF THE PLATES.
Plate III.

Figs. 1 and 2. Echinocystites pomum.-Internal impressions of the oral and apical hemispheres of the same individual. In the Queen's College Museum, Belfast.

Fig. 3. Echinocystites pomum.-Impression of the internal surface; 3 a, one of the pairs of jaws enlarged. This specimen is in the Jermyn Street Museum.

Plate IV.

Fig. 1. Echinocystites pomum.-In the Queen's College Museum, Belfast. Fig. 2. Portion of the impression of the outer surface of the test, enlarged to twice the natural size, and slightly restored, from a fragment in the Ludlow Museum. For the use of this, and of several other specimens, I am indebted to the kindness of Mr R. Lightbody of Ludlow.

Fig. 3. A single plate and spine, much enlarged.

Figs. 4 and 5. Echinocystites uva.-In the Queen's College Museum, Belfast. Figs. 6 and 7. Palæodiscus ferox (Salter).—In Queen's College Museum, Belfast. Fig. 8. Palæodiscus gothicus (n. sp.)-In Queen's College Museum, Belfast.

118

An Account of Two Artificial Hemispheres representing graphically the Distribution of Temperature and Magnetism from the Earth's Equator to the North Pole. By JAMES D. FORBES, D.C.L., LL.D., Principal of the United Colleges of St Salvator and St Leonard's, St Andrews, late Professor of Natural Philosophy in the University of Edin.

These representations of the Climate and Magnetism of the more important and accessible of the two terrestrial hemispheres, have been drawn on a plan somewhat new by Messrs W. and A. K. Johnston of Edinburgh, under my direction and superintendence. They were intended for the Natural Philosophy class, as illustrations of my lectures. The diameter of the hemispheres is thirty inches. They are mounted on square flat boards.

The advantage of delineating the climatological and magnetic curves upon the surface of a sphere instead of on Mercator's charts (as is most usually done), is well known. Indeed, unless by employing two different projections, it is impossible to form a correct idea of the totality of these complicated curves.

Another difficulty is to represent on one surface several different systems of lines, so that they may distinctly convey to the eye the collective results for each independent element. With only two systems of lines this may be done easily enough; but when a third is introduced, there is commonly much confusion. The plan which has been successfully adopted is the following:

On the Climatological hemisphere, the common isothermals from 5° to 5° centigrade, or from 9° to 9° of Fahrenheit (taken from M. Dove's charts), are represented by solid shades of sepia, increasing in intensity with the degree of cold. By this means the deepest shadow covers only an insignificant part of the Arctic regions. The isothermals for January and July respectively are represented by curves of bright blue and bright red, which neither interfere with one another nor with the brown shading.

In the magnetical hemisphere, the sepia tinting is very

suitably appropriated to the increasing gradations of total magnetic intensity from 0-9 to 1.85 of Baron Humboldt's. Unit of force, which gives, for the total intensity at Paris, the number 1.348. The two remaining elements of Dip and Declination are represented by blue and red lines respectively. As to the last of these elements, the position of the horizontal needle at any point of the earth's surface, I have preferred the system of lines drawn everywhere parallel to the needle's direction, to the more artificial system of lines passing through points of equal magnetic variation or declination, according to the method of Halley. The former mode of graphical representation has the advantage of possessing a more distinct physical significance. I have, however, added to the preceding three systems the curve of No Variation, which does not interfere with any of the others, and, being shaded with green and purple on the two sides, distinguishes the regions of easterly from those of westerly declination.

As to the sources from which the previously described lines have been taken, the isothermals have all been derived from the most recent charts of M. Dove: namely, for the lower latitudes, the chart accompanying his work "On the Distribution of Heat over the Surface of the Globe;"* and for latitudes of 50° and upwards, the chart on a polar projection included in his "Klimatologische Beiträge." I examined Mr Blodgett's charts of the isothermal lines of North America, with a view to make use of them; but I was not satisfied that they could be considered strictly comparable with the charts of M. Dove; and in particular, it appeared to me that a reduction to the level of the sea had not been allowed for; at least sufficiently, if at all.

The isodynamic Magnetic Curves, as far as latitude 60°, are taken from General Sabine's chart of 1856, in Johnston's Physical Atlas, together with the Magnetic Survey of North America by the same author in the Philosophical Transactions for 1846. For the extreme arctic latitudes, the curves have been completed partly from M. Gauss's Theoreti

* London, 1853. Neither the scale nor the execution of this chart allows of all the precision which might be desired.

† Berlin, 1857.

cal Charts, partly from the empirical Polar charts of M. Hansteen* and General Sabine.† The lines of dip, as far as latitude 60°, are taken, like the last, from the Physical Atlas; and beyond that limit, by laying down Gauss's lines, and drawing the continuation of General Sabine's lines, with a general regard to the forms of Gauss's curves.

The third and most generally important of the magnetic co-ordinates, that of the direction of the horizontal needle, presented some difficulties. The charts of Duperrey (published at Paris in 1836), which appear to have been constructed with very great care, are made the basis; but in filling up the spaces to which direct observations do not extend, it seemed desirable to combine their data with the theoretical lines of Gauss. The chart in Gauss and Weber's Magnetic Atlas, which represents equidistant values of the function

V

R'

gives us a series of lines which are known by theory to be everywhere perpendicular to the direction of the horizontally suspended needle. The lines of Duperrey beyond latitude 60° or 65° were laid down on a polar chart. The Gaussian curves (which ought to be perpendicular to the former) were laid down to the same scale on tracing-paper. The tracing-paper was then tentatively adjusted over Duperrey's lines until an approximation, as good as could be made to perpendicularity, of the two sets of curves was attained, while, moreover, the pole of the direction-curves was adjusted so as very nearly to coincide with Captain Ross's observed position of the magnetic pole. The outstanding deviations of Duperrey's curves from perpendiculars to the Gaussian ovals was then softened by drawing lines slightly differing from the former, but preserving their general form. These latter lines were then laid down in red on the hemisphere. Perhaps, in this process, I have given too much weight to the theoretical as compared to the empirical curves in the Arctic regions. It is well known that Gauss's theory gives a declination in Siberia which differs very sensibly from observation; much more, indeed, than any errors of observation could reasonably * Poggendorff's Annalen, 1833. † Brit. Assoc. Report for 1837. Leipzig, 1840.

occasion. The discrepancy becomes most perceptible when we come to trace the line of No Variation, which, for North Asia, falls in Gauss's charts somewhat to the eastward of what observation warrants.* I have not, however, considered myself entitled to displace the line of "No variation" in any material degree from the position which it occupies in the Russian territory, and which is founded on direct observation. I think it, therefore, right to specify that a certain amount of discordance exists in this region between the position of this line and that of the red curves of the needle's direction.

REVIEWS AND NOTICES OF BOOKS.

The Typical Character of Nature; or, All Nature a Divine Symbol. By THOMAS A. G. BALFOUR, M.D. London: Nisbet & Co. Edinburgh: John Menzies.

This is a work on a theme which is at all times interesting, and especially at the present moment, when society shows, with regard to the relations between the material and spiritual, such an anomalous state of belief. Thus, there are many who repudiate altogether the doctrine of ideal types and of a spirit-world, and who refuse to admit the possibility of design, or of thought, or feeling, in any form, unless a nervous system is given as an antecedent. There are not a few, on the other hand, who claim for themselves the name of spiritualists (but for whom that of spiritists would be more appropriate), who live in the most extraordinary belief as to the nearness and accessibility of the spirit-world to man, and practise upon it in a way that is very strange. And what certainly is not a little curious, there are some in whom these extremes meet, and who, while they reject the doctrine of the supernatural as such, yet believe in the same to a most extravagant extent, provided only they can succeed in construing all to themselves as natural.

Nor is it only popularly and among the half-witted that this contradiction exists and these extremes meet. Among men of science the same field has been entered, and in too many cases with a most unsatisfactory result, inasmuch as many now maintain, as if it were a settled point in the method and logic of science, that every thing and every thought which will bear the name of religious, are * See the contrasted charts of Gauss and Erman in the Report of the Committee of Physics of the Royal Society, 1840.

NEW SERIES.-VOL. XIII. NO. I.-JAN. 1861.

Q