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We have already alluded to the experiments of Mr. Carl Schultz, and annex below a summary of his results.

Mr. Schultz concludes from his experiments, that the loss of illuminating power due to the addition of air to gas, is about one-half of one candle for each one per cent of air added. He makes the very remarkable observation, that, within limits, the addition of air to very rich cannel gas, up to 12 per cent of air, was followed by no loss of illuminating power, but, on the contrary, by a small gain. Thus boghead cannel gas, giving for 88 per cent gas an illuminating power of 27-47 candles, or for 100 per cent gas 31.32 candles, with 12 per cent of air, gave 28-29 candles, showing that 12 per cent of atmospheric air had increased the illuminating power of the flame by 0-82 candles. These results are obtained only by the use of an Argand burner. By substituting an intensity burner for the Argand, the results obtained with gas from boghead conform to the rule of half a candle loss for each one per cent of air. (Rev. Mr. Bowditch also states generally, that "impurities are far less destructive of light in Argand burners.") Mr. Schultz sums up his results in the following propositions:

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1. When coal gas is mixed with atmospheric air, its illuminating power for all five feet burners is reduced in the proportion of half a standard candle to every 1 per cent of air present, except in case of very rich gas burned with a 15 hole Argand.

2. One cubic foot of atmospheric air will destroy an amount of light equal to 10 English standard candles, during one hour.

3. This loss being constant, the percentage of aggregate loss will vary with the illuminating power of the gas used.

While our results confirm in general those of Mr. Schultz in 1860, and of Messrs. Audouin and Bérard, in 1862; it is obvious that the ratio of loss, with equal increments of air added to a 15 candle gas, is by no means constant. The difficulty of obtaining exact results, by the method of mixture of measured volumes is so considerable, especially with quantities below 10 per cent, that the only safe control of the results is that which is obtained by eudiometrical analysis of the several mixtures tested, as was done by us in all cases both before and after the addition of air. It is obvious that the surprising loss of intensity by the addition to illuminating gas of small percentages of air must be owing not merely to the interior combustion due to the presence of oxygen, but still more, probably, to the associated nitrogen which acts not only as a diluent, or deductive quantity, but its specific heat is an actual divisory function in diminishing the flame temperature. The interest

ing observation, first made by Mr. Schultz, that in very rich cannel gas, there is actualy an increase of intensity within certain limits due to the presence of oxygen, suggests another series of experiments with successive additions of oxygen to a gas of high illuminating power, which we propose to undertake at our early convenience, as also another series upon mixtures of progressive quantities of carbonic acid.

May 17, 1869.

NOTE-Erdmann's Photometer (" Gasprüfer") depends on the use of air to destroy the illuminating power of gas. Elster has employed this instrument in a series of researches undertaken to determine the theoretical illuminating power of different materials (Journal für Gasbeleuchtung, Munich, 1862, p. 384, et seq.) After removing the illuminants by sulphuric acid, he found that ordinary illuminating coal-gas required 150 volumes of air to destroy completely the yellow flame of 100 volumes of gas. If the amount of light obtained by the addition of 1 per cent of olefiant gas to the decarburetted gas employed in a definite burner, is called one candle, it was found necessary to add 6.5 per cent of air to destroy the illuminating power of this gas containing one per cent of olefiant gas or to destroy one candle power. As a like quantity of carbon, carried to a white heat, produces always, in a gas burning from the same burner, the same quantity of light, and it requires the same quantity of air to transform it into carbonic acid, we may regard an ordinary 12-candle gas as a mixture of an unknown non-luminous gas, holding in suspension during combustion a quantity of white-hot carbon, equivalent to 12 per cent of olefiant gas, and requiring, consequently, a quantity of air equal to 210 volumes for 100 volumes of gas (88X15 +12X65=210). Each additional candle power requires an addition of 5 volumes of air, as the constant indicated by these results of Elster. [Translated from Schilling, French Edition of 1868.]

In the use of the Erdmann apparatus, it is found that the volume of air required completely to destroy the illuminating power of coal-gas ranges from 188 to 245 volumes per 100 volumes of gas, varying with its richness.

These results, it will be observed harmonize in a satisfactory manner with those obtained by us, as embodied in Table I.

Every chemist will at once recur, also, to the action of air upon gas in the Bunsen burner, in constant use in all laboratories provided with gas-an instrument identical in principle with the Gasprüfer of Erdmann.

ART. V.-Description of a new Species of Protichnites from the Potsdam Sandstone of New York; by O. C. Marsh, Professor of Paleontology in Yale College. (With a plate.)

THE first discovery of footprints in the Lower Silurian of this country appears to have been made in 1847, in the Potsdam sandstone at Beauharnois, Canada East. In 1851 an account of the locality was published by Sir Wm. E. Logan, and with it appeared a short description of the impressions themselves by Prof. Owen, of London, who then considered them tracks of a Tortoise. Subsequent explorations by the Geological Survey of Canada brought to light new localities and additional specimens in the same region, and in the following year

* Read before the Am. Association of Science, Chicago Meeting, August, 1868. + Journal of the Geological Soc. of London, vii, pp. 247 and 250.

the geological age of the strata containing them was fully discussed by Sir Wm. E. Logan, and a more detailed description of the footprints was given by Prof. Owen, who now regarded them as made by a large crustacean, probably allied to the modern Limulus.* He applied to these impressions the generic name Protichnites, and distinguished six species, or varieties, apparently quite distinct from each other. A trail of a different character was afterwards discovered in the same formation, near Perth, Canada West, and described by Sir Wm. E. Logan, under the name Climactichnites Wilsoni. This was supposed to be the track of a Gasteropod, but Prof. Dana has since suggested that it may have been made by a large Trilobite.§ Up to the present time, eight localities of footprints have been found in the Potsdam sandstone of Canada, along the strike of the formation for about 400 miles, and all at about the same horizon, or within 50 to 70 feet of the top.||

From the Lower Silurian of the United States, no footprints appear to have been described hitherto, although their existence in these strata is now clearly established. An interesting series of impressions was discovered by the writer on the western shore of Lake Champlain, during a visit to that region in August, 1867. They were found on a ripplemarked surface of Potsdam sandstone, just above the then water-line of the lake, a short distance north of the village of Port Kent. The rock is a hard, white quartzite, resembling that containing the footprints in Canada, although probably belonging to a somewhat lower horizon. The impressions obtained, which indicate a new form of Crustacean track, were in two portions, on the same surface, and evidently made by the same animal. They form together a series of footprints, about six feet in length, consisting of two parallel rows of impressions, separated from each other by a space of about one and three fourth inches, and having an extreme width between their outer edges of two and a half inches. Their form and general appearance is represented, one fifth the natural size, in the accompaning plate, which does not, however, give all of the minor impressions.

One of the most striking features of this series, which readily distinguishes it from the Protichnites already described, is the absence of a medial trail, or tail-mark. No indication of such an impression can be detected, even when the track passes over the ridges of the ripplemarks, where it certainly would be *This opinion has since been confirmed by Dr. J. W. Dawson, after an examination of the tracks of a living specimen of L. polyphemus. Canadian Naturalist, vii, p. 271.

Journal of the Geological Soc. of London, viii, pp. 199 and 214.

Canadian Naturalist, v, p. 279, 1860.

Manual of Geology, p. 189. Geology of Canada, 1863, p. 108.

so, we avail ourselves of this opportunity to express our thanks to Mr. Wachsmuth for the zeal, industry, skill and intelligence he has brought to bear, in collecting and preparing for study, such an unrivaled series of the beautiful fossil Crinoidea of this wonderfully rich locality. Some idea of the extent of his collection of these precious relics may be formed, when we state that of the single family Actinocrinide alone, after making due allowance for probable synonyms, he must have specimens of near 150 species, or perhaps more, and many of them showing the body, arms and column.

It is also due to Mr. Wachsmuth, that we should state here that he is not a mere collector only, but that he understands what he collects, and knows just what to collect, as well as how to collect.

Below we give substantially some notes of observations made in his collection, followed by some remarks on other specimens at Springfield:

1. Synbathocrinus Phillips.-Some of Mr. Wachsmuth's specimens of a species of this genus show that it is provided with a long, slender, pipestem-like ventral tube, or proboscis, apparently equaling the arms in length. Also, that a double row of minute alternating marginal pieces extends up within the ambulacral furrows of the arms, apparently all their length. We are not aware that these characters have been hitherto noticed in any of the publications on this genus. It will be seen, however, farther on, that minute marginal pieces probably occupied the furrows along the inner side of the arms of other types of Crinoidea, as well as this.

2. Goniasteroidocrinus Lyon and Casseday.-Some unusually fine specimens of the typical species of this genus (G. tuberosus) in Mr. Wachsmuth's collection, from Crawfordsville, Ind., show the slender pendent arms much more distinctly than any we had before seen, and from these it seems evident that these arms are stouter than we had supposed, and that there are not more than five or six of them to each of the ten openings. In the specimen figured by us on page 220 of the second volume of the Illinois Reports, these arms were only imperfectly seen by working away, with great difficulty, the hard matrix between two of the produced rays of the vault, which we have termed pseudobrachial appendages, or false arms. In clearing away the matrix of this specimen, we had cut just far enough to expose the edges of the arms on each side of the deep ambulacral furrow, so that each of these edges presents the appearance of being a separate and distinct, very slender arm, composed of a single series of pieces, and without any ambulacral furrow on the outer or ventral side; whereas there is a well-defined

ambulacral furrow, bearing the tentacula along its margins, on the outer side of the arms, and when the matrix is removed from these ambulacral furrows, the arms can be seen to be composed each of a double series of small alternately-arranged pieces. It is barely possible that in specimens of this species with the arms perfectly preserved, the ambulacral furrows may be covered on the outer or ventral side by a double series of alternating pieces, and that the tentacula may connect with little openings along each side, though there certainly appear to be only open furrows in the specimens examined.

It is worthy of note, in this connection, that there certainly are species, agreeing exactly in all other known characters with this genus, that have no open furrow along the outer or ventral side of the arms, which are distinctly seen to be round on the outer side, and show there a double series of interlocking pieces along their entire length, while the tentacula connect along the inner, or under side, as the armis are seen hanging down. This is clearly seen to be the case in a beautiful specimen of G. typus (=Trematocrinus typus Hall) in Mr. Wachsmuth's collection, and we can scarcely doubt that in this species there is an open furrow on the inner (under) or dorsal side of the arms. If not, the arms must be tubular, in consequence of having the ambulacral canal enclosed all around, excepting at the points where the tentacula connect along each side.

3. Cyathocrinus Miller. Specimens of this genus showing the vault (more properly the ventral disc) have very rarely been seen. In England a few examples have been found, and these have been supposed to show two openings, one central and another lateral; the latter, according to Prof. Phillips' and Mr. Austin's figures, being provided with a slender marginal tube, or so-called proboscis. Some of Mr. Wachsmuth's specimens, however, of C. malvaceus and C. Iowensis Hall, showing the vault, have led us to doubt the existence of a central opening in the vault of this genus, when the specimens have this part entire. The specimen of C. malvaceus shows the remains of the usual narrow lateral proboscis, and also has an opening in the middle of the vault, but from the appearance of this opening, as well as from the structure of the vault of a specimen of C. Iowensis, in which this opening is closed, we can scarcely doubt that it was also closed in the specimen of C. malvaceus, when entire. The remaining parts of the vault of the C. malvaceus mentioned consist of only five comparatively large pieces, alternating with the upper inner edges of the first radial pieces,

* We use the term tentacula here in the sense it is generally used by paleontologists, with reference to the delicate pinnulæ along the arms of Crinoids, and of course not as applying to the minute fleshy organs along the ambulacral furrows, usually termed tentacles by those who have investigated the recent Crinoids.

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