Fig. 8. Silicious, single-pointed, straight, moniliform spiculum of the Spongia monile, Gr. (See Edin. New Phil. Jour. vol. i. p. 348.)

Fig. 9. Silicious, single-pointed, curved, long spiculum of the Spongia sanguinea, Gr. (See zoological notices at the end of the present Number.)

Fig. 10. Silicious, curved, short spiculum, obtuse at both ends, of the Spongia fruticosa. (See Edin. New Phil. Jour. vol. i. p. 350.) For the S. hispida the same form occurs, but more than double this length.

Fig. 11. Calcareous triradiate spiculum of the Spongia compressa. (See Edin. New Phil. Jour. vol. i. p. 166.)

Fig. 12. Calcareous, clavate, curved spiculum of the S. compressa. (Ibid.)

Fig. 13. Calcareous, straight, very minute spicula of the S. compressa. (Ibid.)

Fig. 14. Calcareous, triradiate, large spiculum of the Spongia nivea. (Ibid. p. 168.)

Fig. 15. Calcareous, quadriradiate, minute spiculum of the S. nivea. (Ibid.)

Fig. 16. Calcareous minute fragments of triradiate spicula of the S. nivea. (Ibid.)

Fig. 17. Calcareous triradiate slender spiculum of the Spongia coronata. (Ibid. p. 170.)

Fig. 18. Calcareous, single-pointed, slightly curved long spiculum of the S, coronata. (Ibid.)

Fig. 19. Horny tubular thick fibres of the Spongia fistularis. (See Edin. Phil. Jour. vol. xiv. p. 339.) a. Amber-coloured horny translucent parietes. b. Dark opaque granular matter filling the central cavity.

Fig. 20. Horny tubular thin fibres of the Spongia communis. (Ibid.) a. Amber-coloured transparent parietes. b. Empty central cavity.

Fig. 21. Living Spongia papillaris under water, shewing its mode of generation, &c. (See Edin. New Phil. Jour. vol. ii. p. 133.) a, a, Minute pores through which the currents enter. b, Commencement of the internal canals. c, Uniting of the internal canals to form a fecal orifice. d, A fecal orifice discharging a current of water with feculent matter. e, A fecal orifice discharging two ova and feculent matter with the current. ff, Groups of mature ova. g, Ovum passing into a canal. h, Gelatinous base connecting this animal to the rocks.

Fig. 22. Living Spongia oculata, shewing its currents, mode of generation, &c. a, a, Minute pores transmitting water obliquely into the canals. b, b, Fecal orifices discharging currents, feculent matter, and ova. c, Strong fibrous part of the animal by which it hangs from rocks.

Fig. 23. Living Spongia compressa, with a part of its side laid open, to shew the terminations of its canals in the interior of its general cavity. a, Expanded base by which it hangs from rocks, fuci, &c. b, Compressed terminal opening of its general cavity, by which the currents, ova, and feculent matter, finally escape. c, Minute pores by which the water passes obliquely through its parietes. d, A part laid open, to shew the fecal orifices terminating in the general cavity of the animal.

Fig. 24. A pore of the Spongia panicea highly magnified, to shew (a) its bounding fasciculi, and (b) a defending fasciculus spread over a gelatinous network.

Fig. 25. A pore of the Spongia papillaris, highly magnified, to shew (a) its bounding fasciculi, (b) the part where the bounding fasciculi cross each other to form recesses for the ova, and to which the connecting matter of the spicula was supposed to be confined, and (c) the most usual appearance of the gelatinous network of the pores in this species.

Fig. 26. A transverse section of an internal canal of the Spongia papillaris. a, Its bounding fasciculi, covered with the very minute monade-like bodies composing the parenchymatous matter. b, Groups of imperfectly formed ova lying in recesses of the parenchymatous matter. c, Simplest form of the gelatinous network found within the canals. d, Ova hanging by their tapering extremity to the side of the internal canal, and producing currents by the motions of the cilia covering their free surface.

opaque part occub, Zone of vibrating

Fig. 27. Highly magnified ovum of the Spongia panicea, viewed from above, when about to fix. a, Central pied by spicula, and covered with ciliæ. ciliæ distinctly seen round the margin. lated sediment, produced by the cilia space next the ovum.

c, Zone of accumuconstantly clearing the

Fig. 28. Highly magnified ovum of the Spongia panicea, viewed laterally, to shew its entire ovate form. a, Ciliæ, longest on the vertex of the ovum, and resting on a more translucent part of the ovum. b, White pellucid base by which the ovum fixes

and expands. c, The part where the white base commences, and where the cilia seem to terminate.

Fig. 29. Appearance of the young Spongia panicea, after the ovum has fixed and spread for fourteen days on a watch-glass. a, Central opaque part to which the spicula were at first confined. b, Transparent homogeneous margin by which the young sponge spreads, and which likewise produces spicula. c, Halo of accumulated sediment frequently seen round the margin, at a little distance from the young sponge, and inclosing a cleared space, as in Fig. 27. d, The part where the monade-like parenchymatous matter terminates, and where the colourless homogeneous matter commences.

Enumeration of the Instruments requisite for Meteorological Observations; with Remarks on the mode of conducting such Observations. By Professor LESLIE.

EVERY

meteorological observatory, if it shall register with accuracy, and in a complete and satisfactory manner, the various atmospheric phenomena, ought to be provided with the following instruments.

1. The barometer, which measures the pressure of the atmosphere; 2. The thermometer, which indicates its degree of heat; 3. The hygrometer, which marks its relative dryness; 4. The atmometer, which measures the quantity that evaporates in a given time from the surface of the earth; 5. The photometer, which indicates the intensity of the light transmitted from the sun, or reflected from the sky; 6. The athrioscope, which detects the cold showered down from the chill regions of the higher atmosphere; 7. The cyanometer, which designates the gradation of blue tints in the sky; 8. The anemometer, which measures the force and velocity of the wind; 9. The ombrometer or rain-gauge, which marks the daily fall of rain, or haill, or snow; 10. The electrometer, which indicates the electrical state of the air;

* In a close room or sheltered in external air, the atmometer the place of an hygrometer; and compared with another one fr it might serve as a substitute for the anemometer.

tance.

and, 11. The drosometer, which measures the quantity of dew. These various instruments are not, however, all of equal imporThe barometer, the thermometer, and the hygrometer, may be considered as quite indispensable. Next to them, deserves to be ranked the photometer and athrioscope, which disclose the more recondite condition of the atmosphere. The atmometer, the ombrometer, and the anemometer, are of great consequence, from the practical results which they furnish. I would strongly recommend, as a most useful auxiliary in meteorological observations, Rutherford's maximum and minimum thermometer. In many cases, likewise, it would be convenient for the scientific traveller to be provided with a thermometer bearing large divisions, and lodged at the bottom of a walkingstick, protected by a coating of down inclosed within a brass tube. This instrument is peculiarly adapted for exploring the temperature of the ground and of springs*.

But the value of any meteorological register must depend on the accuracy with which it is kept. The observations should be made in a place rather elevated, sheltered from the direct action of the sun, but exposed freely on all sides to the aspect of the sky; and they should be repeated either at equal intervals, during day and night, or at least at those hours which represent most nearly the mean state of the atmosphere. These requisites are seldom attained, and very few registers of the weather, accordingly, are entitled to much confidence.

It cannot be expected, that registers of the weather will possess much value, so long as they are kept merely as objects of curiosity. Like astronomical observations, as now conducted, they should no longer be left to the chance of individual pur

• It would be particularly desirable, if travellers over land were provided with light barometers and staff-thermometers. A very portable barometer, sufficiently accurate for general purposes, might be constructed with a conical tube, or two portions of unequal diameters conjoined. But the staff-thermometer might often supply the want of a barometer, by discovering the mean temperature at moderate depths under the surface. Hence the relative altitudes of different places above the level of the sea could be estimated with tolerable precision. Had the various travellers who have visited the Interior of Africa made observations of that kind, the question respecting the course of the Niger would have been decided long before now; at least we should have known, whether the great lakes were, like the Caspian, below the surface of the ocean.

suit. They would require to be unremittingly prosecuted, in all variety of situations, and at the public expence. Proper sets of meteorological instruments should be placed, not only in the regular observatories, but sent to the different forts and light-houses, both at home and at our principal foreign stations. They might also be distributed among the ships employed in discovery, or engaged on distant voyages. The cost of providing those instruments would be comparatively trifling; and the charge incurred, by conducting registers on a regular and digested plan, might shrink almost to nothing in the scale of national expenditure *.

The state of the barometer alone is now kept with tolerable accuracy, because that instrument, being little influenced by adventitious circumstances, marks nearly the same impressions over a wide extent of surface. The thermometer, again, is seldom observed at the proper hours, or in situations sufficiently detached from buildings and solid walls.

It is customary, for the sake of convenience, to note the thermometer in the morning, at the height of the day, and again in the evening. But these three observations must evidently give results below the medium temperature of the whole

Government provided our discovery ships, sent to the Arctic seas, with meteorological instruments; but these, owing either to the ignorance or carelessness of the makers, were, in some instances, discovered to be very inefficient. Thus the thermometers were found to differ from one another ten degrees, and the Six's thermometers used for ascertaining the temperature of the sea at different depths, were not trustworthy. In future experiments with Six's thermometer, we would recommend correction to be made for the effect of the compression of the water against the bulb, as had been carefully done in Lord Mulgrave's voyage to those regions. Captain Parry carried out, in his second expedition, two sets of hygrometers, photometers, and æthrioscopes; but these instruments, it seems, were entrusted to the charge of the astronomer, who either broke or neglected them. Yet a connected series of observations, performed with such instruments in the Polar Regions, would have furnished most important data for extending meteorological science.

In a late philosophical voyage, directed to the Equator, some loose attempts have been made to estimate the radiation from the sky. But whatever may be said of the theory of the athrioscope, its great delicacy is beyond dispute; and for an observer to overlook or disregard such an instrument, seems about as reasonable as if a navigator should prefer the old crossstaff to the sextant or the repeating circle.