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of the water will be saturated with vapour, and the thermometer will indicate 212°, or boiling point; but there need be no ebullition-if the water be perfectly pure there will be none. (Experiment.) But that the steam is in the innocent-looking liquid will be plain if you introduce a wooden stick or rod. Wherever you place the point, steam collects-where does it come from, if not in the water? the cool rod cannot generate it. To make this more clear, let us take a vessel in which a permanent source of attraction is set up in the form of a cross made of pounded brick, stuck on by paint. It is thus shewn, says Mr. Williams, "that the ebullition is purely accidental, and has no reference to the generation of vapour, and that it is solely the result of the aggregation of myriads of atoms previously formed, and irrespective of the heat transmitted and absorbed in any particular locality."

To shew the force of the ascensional power of steam atoms, Mr. Williams puts a quantity of pounded coal into a vessel of water, through which the steam forces its way-forcing the particles upwards like so many explosions.

Mr. Williams denies that water is expansible, as it is acknowledged to be nearly incompressible. He requires the application to liquids of the admitted law as regards solids"that dilatation and compression are correlative terms.”

"If," he says, "dilatation and compression are treated as being reciprocal and proportionate when spoken of in relation to solids, why draw a contrary inference in relation to liquids? If iron contracts considerably under cold, and expands considerably in same proportion under heat, why not say that, as liquids are nearly incompressible, they must be nearly inexpansible?"

Again, water wanting the power of readily conducting heat from one particle to another, cannot communicate a sufficient amount of heat to make the mass expand, as would be the case in a solid; for, if one particle cannot give, its neighbour

cannot receive heat from it. If you insert a long tube in a flask of water, so that the water shall rise a certain height in the tube, and apply heat to the bottom of the flask, the column of water in the tube will at first fall, because the glass, though solid, expands more quickly than the water, so allowing the latter more room; it will soon rise, however, but the expansion is due to the larger bulk of the particles of steam generated, and not to the expanded water.

With regard to condensation, Mr. Williams contends that steam is not condensed by cold water, for several reasons :—

1st. If steam were condensed by contact with cold water, the first steam generated must be immediately condensed by the cold water with which it would be at first in contact; you never could get beyond a succession of vaporisations and condensations—no body of vapour could be formed.

2nd. A small jet of steam discharged into a large body of water is capable of almost instantly raising the whole to 212°. 3rd. Steam, as we have seen previously, may be carried through a series of vessels containing cold water.

I shall only add a short notice of his theory regarding the interesting subject, both to cooks and captains, of Boiler Explosions.

If I rightly understand him it is, that explosions rarely occur from deficiency of water, any further than that such deficiency may cause injury to the boiler plates from over-heating; but they arise from the sudden escape of the steam contained in the water. (Of course, on his principle, the more water the more steam.) If, then, the engine has been at rest for some time, but heat continuously supplied to the bolier, both the water in the boiler and the space above it will be heavily charged with steam; so long as the equilibrium is maintained all will be well; but if, from any cause-such as the injection of water from the feed pipe, producing a tumultuous aggregation of steam atoms, or by opening the valves and starting

the engine-a quantity of steam be suddenly liberated, a tremendous rush of steam, both from the chamber above, and from the body of water, carrying a quantity of the latter with it, and gaining increased momentum on escaping from the denser medium, hurls itself with such precipitation at the valve (like a mob to the door where a theatre is on fire), that it misses its object, and is thrown violently against the crown of the boiler; and should any part of this be previously at its maximum strain, the impetus is irresistible.

The paper was illustrated by experiments in proof of Mr. Williams' views, under the charge of Dr. Edwards.

ELEVENTH ORDINARY MEETING.

ROYAL INSTITUTION, 18th March, 1861.

The REV. H. H. HIGGINS, M.A., PRESIDENT, in the Chair.

Mr. T. S. WALKER, M.R.C.S., and Mr. G. SEARLE WOOD, were elected members.

The names of numerous visitors were announced.

Mr. J. O. FABERT exhibited several beautiful specimens of Gorgonia, &c., from the West Indies, and some remarks were made by the Chairman upon their peculiar mode of growth.

Mr. MOORE exhibited a large collection of furniture and ornamental woods, the produce of the Canadian forests. They consisted of forty-five specimens, comprising ash, birch, cedar, elm, maple, chestnut, walnut, oak, &c., and were collected by Mr. William Quinn, supervisor of Cullers, Quebec, who was present, and made some remarks concerning them.

Dr. COLLINGWOOD read an extract from a private letter which he had received from Professor Agassiz, of Cambridge, U.S., in which that gentleman proposed to enter into a correspondence with the society for exchange of specimens between the museums. He had referred the subject to Mr. Moore, of the Derby Museum, by whom it had been warmly taken up, and who had taken advantage of the return of the steamship "Canada" to send the professor a small packet as an earnest of future correspondence. The letter of Mr. Agassiz had been kindly brought him by Captain Anderson, of the Cunard steamship Canada," a gentleman who took a great interest in thesubject of Natural History, and who was willing to be the medium of communication with Prof. Agassiz.

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Dr. COLLINGWOOD also referred to a memorial to the Committee of the Mercantile Marine Association, extracts from which he read to the meeting, in which was proposed a scheme for the encouragement of studies among the captains and sailors of the Mercantile Marine, which might be expected to improve their own morals and benefit science. It further insisted upon the value which would accrue from the more general collection by such men of natural objects from all parts of the world for the enrichment of our museum, and recommended them to avail themselves of the opportunities which would be offered by the proposed School of Science. Dr. Collingwood announced that this memorial had been that day laid before the committee of the Mercantile Marine Association, by whom it was favourably received, and ordered to be printed; and would, moreover, appear in The Albion, of the following Monday (March 25), an announcement which caused general satisfaction to the meeting.

Mr. HENRY DUCKWORTH explained briefly, with the aid of a chart, the leading points in Mr. Consul Petherick's expedition to the sources of the Nile, which is intended as an auxiliary to the prime expedition already dispatched to the

same goal by way of Zanzibar, under the conduct of Captains Speke and Grant. Supported by an escort furnished him by the amiable Prince of Zanzibar, Captain Speke will retrace his steps to the point of his last important discovery, the Lake Victoria, Nyanza. The intervening country being peopled by comparatively friendly tribes, the travellers will experience only the ordinary difficulties of transport during their passage through it. It is in their progress northward to Gondokoro from Lake Nyanza, which will be thoroughly explored with a view to determining whether or not it is the mother of the Nile, that the party will encounter the greatest difficulties, for not only,. according to Mr. Petherick, are the languages of the aborigines different from those known south of the equator, but, unaccustomed to strangers, their hostility towards them, and to neighbouring tribes is very great. Again, unless the expedition reaches Gondokoro in December or January, when Khartoum traders visit the place for the purpose of barter, it will be unable to proceed down the Nile, and, after a drain upon its resources of from twelve to fifteen months (the time which Captain Speke calculated it will take to reach Gondokoro from Zanzibar), its position will be not a little critical. It is at this point that Mr. Petherick proposes to step in. Setting out from Khartoum, his first object will be to form a sufficient depôt of grain at Gondokoro, under the charge of his own men, to ensure to Captain Speke means of subsistence and security from violence whenever he should reach that place. 2ndly. To explore the country between Galuffi and Lake Nyanza; and, 3rdly. To effect a meeting with Captain Speke, and assist him through the hostile tribes between the Lake and the Nile. Mr. Petherick estimates that the cost of this additional expedition will be only £2,000. "Spes sit mihi certa videndi Niliacos fontes, bellum civile relinquam," are words which Lucan has put into the mouth of Julius Cæsar; but, judging from the manner in which the people of

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