In none of these particulars has it any relationship with polyzoa; but the mouth is surrounded with a circlet of tentacles, not indeed like those of the polyps, simple and contractile, but uncontractile and covered with vibratile cilia. They are probably the homologues of the labial palpi of other molluscs. This circlet of tentacles, then, is the great point of resemblance between molluscoids and polyps; in the latter the common arrangement-in the former, arising as it were from an accident or variety of organization. But yet, is it not easy to perceive that the common possession of tentacles exhibited by polyps and polyzoa implies a very great similarity, nay, almost identity, in one of the most important habits, namely the mode of procuring food?

Having so far established a community of habit between them, let us next refer to the grand organic distinction which is implied in the widely different form of the digestive apparatus. In the polyps, the rejectamenta being passed out by the mouth, such animals are well fitted, doubtless, for living in cells with a single aperture; the mollusca, however, have an intestinal canal, and anal aperture besides. But it must be borne in mind that the anus in the polyzoa does not open at the extremity of the body opposite the mouth, as in the archetypal mollusc; but by a sudden bend of the intestine, the anal aperture is brought into the closest possible proximity to the mouth; so that, although separate, they both open at the same spot; and let it not be supposed that this diminishes aught from their position as molluscs, for in the highest molluscs, viz., the cephalopods, the same thing takes place in a somewhat less degree. Here again is a structure which implies great community of general habit. Lastly, there is another most important community of habit between the polyps and polyzoa, viz., that although the mollusca, as a class, are oviparous, the polyzoan molluscs are, in addition, gemmiparous, like the polyps; and this power is evidently the

secret of the production of those compound forms which the polyzoa present in common with polyps. Hence we see that with scarce anything in common, except superficial characters, the habits of polyzoa and polyps are nearly identical; and to this fact I would look for an explanation of their identity of form.

In conclusion: Lord Bacon has somewhere remarked that experiments and observations are of two kinds, viz., first of fruit, and second, of light-by which he meant that some led directly to some plain and definite ends, which amply repaid the labour bestowed upon them; while others, by no means to be despised, yet were not so obviously accompanied by actual fruit. Far be it from me to raise homomorphism to the rank of homology; I have endeavoured throughout to place them in strong contrast; and although I do not wish to forego all claim to fruit from these observations, I am willing to allow them rather to belong to the second category. But I cannot sympathize with those who would taboo such curious questions, simply because some others lead to more important results. Everything in Nature is worthy of investigation, and although I may not have succeeded in fully tracing out the law of order which probably exists in these homomorphisms, still I have by the enquiry improved my own knowledge of Nature, and have given, I trust, an insight into the creative workings of the Almighty, which cannot fail to increase the desire to be more closely acquainted with them. Surely, human works fall infinitely short of the surpassing interest which appertains to those of the Great Artificer; and human history is but a line in the great scroll of the universe, which has been inscribed from the beginning with the works of the Creator. Let no one presume ignorantly to contemn, or

For an example of such reasoning, see Bain "on the Senses and Intellect," p. 499, where the writer of that generally excellent work argues rather as the disciple of a severe school of logic, than as a loving and humble follower of Nature.

conceitedly to overlook the stupendous work of creation, of which man is the keystone and the crown but if ever he be tempted to assert his superiority by underrating the matchless perfection of Nature, let him humble himself in the dust, when he remembers that the God who formed him looked upon all the things which he had made, "and behold they were very good."

THIRTEENTH ORDINARY MEETING.

ROYAL INSTITUTION, 2nd April, 1860.

The Rev. H. H. HIGGINS, M.A., President, in the Chair.

The Chairman alluded to the interview of a deputation from several learned societies in town, with William Brown, Esq. and the Town Council, relative to a contemplated plan of setting apart a portion of the Free Public Museum for the display of models and scientific objects applied to purposes of utility.

The Chairman also drew attention to the development of medusæ, from Hydra tuba in the aquarium under Mr. Moore's direction in the Derby Museum.

Mr. JAMES YATES, F.R.S., corresponding member, attended the meeting, and spoke on the question of a decimal system of measures, time, and money, referring to Mr. Statter's plan of employing the equatorial circumference of the earth instead of its polar axis, as the basis of his unit.

The Secretary exhibited and described a working model of Newcomb and Lovell's engine, for using water as a motive power. The chief peculiarity was the adaptation of a donkey

engine to the cylinder, so that with but one cylinder the work of two could be obtained. The small steamer exhibited had been tried a few days before upon the lake in the Prince's Park, and made fair speed.

The following Paper was then read

ON THE RELATION BETWEEN

ATMOSPHERIC PERTURBATIONS & EXPLOSIONS OF FIRE-DAMP IN COAL MINES.

BY THOMAS DOBSON, Esq., B.A.CANTAB.

THE inquests which follow fatal explosions in coal mines seldom elicit much information respecting the ultimate causes of these disasters. The proximate cause even is in general left to conjecture. Some miner in whose "board" the "foul air" appears to have first "fired," is supposed to have been working at the time with a naked light. But as it is notorious that miners run this risk habitually, either from carelessness, or from a dislike of the faint glimmering given by a locked Davy-lamp, it would seem reasonable on such occasions to make the investigation bear more directly on the question, "how did it happen that the atmosphere of the mine was in such an exceptional state as to explode without any unusual exposure of lights?"

In many dangerous mines Davy lamps are only used in the "pillar" workings, which lie in, or near to the "goaves," or abandoned wastes,-reservoirs of many acres in extent, where the carburetted hydrogen gas accumulates undisturbed; while naked candles are always used in working the new coal. This is the ordinary state of things, and the probability of an explosion occurring soon after any extraordinary flow of gas

into the mine is evident, when it is considered that the Davy lamp itself is by no means perfectly safe, and that the light inflammable gas may easily travel gradually along the roof of the passages of the mine from the goaf to the parts where naked lights are being used.

There is only too much reason to fear that at such inquests the viewers and inferior officers of the mine, seeing their professional reputation at stake, unite in defeating the enquiry by withholding information, and that the owners are not unwilling tacitly to sanction a line of conduct which tends to protect them from the consequences of an unfavourable verdict.

One of the last things to be admitted by the manager of an exploded mine at an inquest, would be the direct agency of atmospheric disturbances in causing the accident; for as such disturbances may be foreseen, and their consequences in mines prevented, the neglect implied by such an admission might help to lead to an adverse verdict, and to a compulsory provision for the widows and fatherless children of the men killed by the explosion.

Nevertheless, the belief that atmospheric fluctuations are in some manner principally concerned in causing these disasters has long prevailed among the most intelligent mining agents, viewers, and practical miners, as is abundantly shown by the evidence given before the several Committees of both Houses of Parliament appointed from time to time to enquire into the subject of accidents in coal mines.*

The following were quoted from authentic records. (Blue Book):—

In 1835, 4. Winship, wasteman in Lord Durham's mines, says-"we generally think that the hydrogen gas is more quick and severe when the wind is from the south.

Nicholas Wood, colliery viewer to Lord Ravensworth and Co., says—“ a fall in the barometer occasions a considerable change in the quantity of gas discharged; if the barometer rises, the gas then withdraws to the old workings, and does not come out in such quantities. Hydrogen gas exists in the pores of the coal in a state of high compression, if the external pressure is removed, it issues in greater quantities, and we accordingly find a very much greater discharge by the fall of the barometer."

The evidence of George Stephenson is very clear on this point, he says-"I believe that accidents of this kind, of any extent, very rarely happen except when