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ADDRESS LITTELL & CO., 31 Bedford St., Boston. hihi, Unlest, THE AMERICAN JOURNAL OF SCIENCE. [THIRD SERIES.] Art. I.—Observations on Invisible Heat-Spectra and the recog- nition of hitherto. unmeasured Wave-lengths, made at the Alle- gheny Observatory ;* by S. P. Laneuey, Allegheny, Pa. With Plates I to IV. It is known to all, that the surface temperature of this planet depends upon the properties of radiant heat and the relation to them of the action of its atmosphere. It has been usual to compare this action to that of the glass cover of a hot- bed; for glass, it is also well known, grows opaque to dark heat, and continuously so, as its wave-length increases, thus letting the solar light-heat pass freely through it to the soil, while it is comparatively impervious to the dark heat returned from the latter; but this analogy must not be interpreted too literally. Whether the atmosphere is pervious to the soil’s heat we do not here discuss, but it has of latet been shown that the air does not behave otherwise like glass as it was supposed to do, but except for the absorption bands, grows—not more opaque—but more transmissible, to solar heat, up to its greatest observed wave-length, and that hence our views of the nature of the yet uncomprehended heat-storing action which maintains organic life on the earth must be modified. The little that the spectroscope tells us about the atmospheres of other planets, leads us to think that we can best understand their relations to solar energy by studying the atmosphere of our own; for our non-comprehension of these relations is largely due to our * Read before the American Association for the Advancement of Science, at Ann Arbor, + See this Journal, March, 1883, Professional Papers of U. 8. Signal Service, No. 15, Expedition to Mount Whitney. Am. Jour. Sct.—TuIrD SERIES, VOL. XXXI, No. 181.—Jan., 1886. 1 2 §. P. Langley—Observations on Invisible Heat-Spectra. ignorance of certain physical data which have never yet been obtained. While the general question for the physical astronomer then, is “ What kind of transformation does the solar energy suffer at the surface of any planet?’’ we here seek a reply to the simpler preliminary one, ‘‘ What are the wave-lengths of heat from non-luminous sources, such as the soil of this planet?” a question which has never been answered, because there have been no means of recognizing this heat when drawn out into a spectrum ; indeed we so habitually associate the idea of a spec- trum with that of light, that there is a certain strangeness, at first in the idea even, of a ‘‘spectrum” formed by a cold body like, for instance, ice. Yet the ice surface must not only be capable of radiating heat toa still colder body, but according to our present conceptions of radiant energy, be capable of . giving a spectrum, whether we can recognize it or not. It is the object of the present paper to describe the actual formation of such spectra, and the recognition of their heat in approximate terms of wave-lengths. ; To distinguish between these new regions of research and the older ones, let us briefly summarize our actual information about wave-lengths, since on the latter the whole question largely turns, and each extension of it, we may agree, is a step toward an interpretation of everything about the constitution of the universe which radiant energy may have to tell us. Thus there is no exact relation known between the periods of vibration of certain molecules in the sun and the angles through which the rays announcing them, are refracted by a prism, while the wave-lengths of these rays, if known, are capable of giving us quite other intelligence. Yet our knowledge even of the wave-lengths of light is com- paratively recent, since it was only at the beginning of this century that the labors of Thomas Young brought the undu- latory theory itself from the disfavor in which it bad lain, and the memoirs in which Fraunhofer gave the first relatively full and accurate measures of the wave-lengths of light date no farther back than 1814. The measures of Newton, interpreted in terms of the present theory, gave the length of the extreme violet waves at iv,veaso7 Of an inch, and of the extreme red at 75, 278s00, OF in millimeters 0:00042™ and 0:00067™™ respectively, numbers nearly corresponding with the lines H and B, while Fraunhofer’s own values are comprise between 0:000386™™ and 0-00075™™. More recently the range of vision has been still more extended, by the use of the fluorescent eyepiece of Soret, while by the aid of photography and the employment of quartz trains, solar radiations of a wave-length of about 0:29 # have been observed,* * (1:0 u=0-001™™)4 a S. P. Langley—Observations on Invisible Heat-Spectra. 3 and, rays whose wave-length is as little as 0°185 y have, it is said, been observed from the induction spark. Our atmosphere cuts off the ultra violet rays of a length less than about 0:29 yw, while I have found it not very difficult to see, below Fraunhofer’s great A, lines whose wave-length is about 0°81 4. The extreme range of the normal eye then, is from about 0:00036 to 0:00081™™, or a little over one octave, though the statement that the range of the eye is less than one octave is still commonly made. Fraunhofer’s first measures were made with a literal grating composed of parallel strands of wire, while the successive labors of Nobert, Rutherfurd and Rowland have placed in the hands of physicists instruments of constantly increasing power, which have finally reached what seems nearly theoretical perfection at the hands of the two latter. It is with the now so well known gratings of Professor Rowland that the direct measures of wave- lengths in the solar heat spectrum I have already made public* have been chiefly executed. In Plate I we have a necessarily condensed representation of the whole spectrum, visible and invisible, on the normal scale, the distances being proportional to the wave lengths observed. The inferior limit being 0, we have at (a) the number 0°18 pz (eighteen one-hundred thousandths of a millimeter), which represents the shortest measured in the electric spark from aluminum. Next near 0:29 wu (b) we have, according to M. Cornu, the shortest solar ray which penetrates our atmosphere; near 0°35 yw (c), in the ultra violet, is the shortest wave which can be seen by the naked eye, and nearly the shortest which can pass through glass, while near 0°81 y (d) in the extreme red, is nearly the longest which the eye can observe. The entire visible spectrum on the normal scale is, it will be seen, insignificant in comparison with that great infra-red region which is so important to us, and of which we know so very little. It has been known since the time of the first Herschel that heat rays existed below the range of vision, but of their wave-lengths nearly nothing has, till lately, been ascertained, partly for want of sufficiently delicate heat-recognizing apparatus, and still more from the fact that it is difficult to use‘the grating here, owing to the overlapping spectra, and to the consequent necessity we have till lately been under, of separating these rays only by the prism, which gives no measure of their wave- lengths. Physicists have accordingly attempted to find these, by observing what deviations correspond to known wave- lengths in the visible portion, and by trying to determi.e, from theoretical considerations, what relations should obtain in * Comptes Rendus, Sept. 11, 1882. National Academy of Science, 1883. This Journal, March, 1884. 4 §. P. Langley—Observations on Invisible Heat-Spectra. the infra-red, but the various formule by which these supposed relations have been expressed have not till lately been tested. The difficulty has been partly overcome in the last few years, by the application of the linear bolometer to the spectrum formed by the concave gratings with which Professor Rowland has furnished us; the deviations of the heat rays having first been observed and the principal lines of the infra-red region mapped by the joint use of the bolometer and a flint glass prism, in 1881. It will be remembered that one of the best known formule on which physicists have till lately relied for determining the relations of wave-lengths to deviations was Cauchy's; that this set an absolute limit to the wave-length which any prism could under any circumstances discriminate, and that this supposed extreme wave-length was somewhere between 10,000 and 15,000 on Angstrém’s scale. Besides this theoretical limit, it was supposed that glass absorbed dark heat to such an extent, that the longer solar heat waves would be stopped in the substance of the prism, even were there no otber obstacle. In 1881, however, we found at Allegheny by actual trial, that heat waves whose wave-length was far in excess of the theoretical limit, passed through a flint glass prism, so that it was ascertained both that this supposed limit did not exist, and that common glass was comparatively diathermanous to all the dark heat which comes to us.from the sun. By means of a glass prism and the bolometer, we were thus able to pursue our researches and map the infra-red or invisible solar spectrum to a point where it actually came to an end. What the wave- length of this point was we could not tell, for it lay entirely outside of what theory had till then pronounced possible. Next, using the grating, we have at Allegheny determined the wave-lengths of most of the newly discovered solar heat region, by direct observation, and shown that it extended to the unanticipated length of 2”-7 (e, Plate I) (1 e., 27,000 on Angstrom’s scale.) I cite these facts, which bave already been published, to bring us up to the point where the present researches begin. The question now arises, ‘‘ Does this ultimate observable wave-length of solar heat of 2u-7, which our atmosphere trans- mits, correspond to the lowest which can be obtained from any terrestrial source, or are the wave-lengths emitted from our planet toward space, even greater, and conceivably such that = our atmosphere is nearly athermanous to them?’ To answer this it becomes necessary to do what I think has not been attempted before: to take a source of very low temperature, comparable to that of the soil, and not only to measure its ex- tremely feeble invisible heat, but to draw this out into a spec- S. P. Langley—Observations on Invisible Heat-Spectra. 5 trum by means of a prism or grating, and to determine the indices of refraction of its prominent parts, and by inference, their wave-lengths. We have now been engaged on this re- search at Allegheny at intervals for two years, a time which will not appear extravagant to one acquainted with its extreme difficulties. Not to dwell on these in detail, I will mention, only, that the grating can not well be used on account of its overlapping spectra, if for no other reason, and that the most transparent glass, which we have found to be comparatively diathermanous to dark solar heat, turns out to be. almost absolutely athermanous to the heat from a surface at the tem- perature of boiling water. Glass being useless here, almost the only material of which we can form our prism is rock-salt, and we must have not only an entire train of lenses (both collimating and observing) of salt, as well as the prism, but the pieces must be of exceptional size, purity and perfection of figure, to contend with these special difficulties, and they must be maintained in condition, in spite of the incessant deterioration of thissubstance. Tinally, as we wish to determine wave-lengths, these measures must be very accurate, and the prism be capable of giving fixed points of reference like the visible Fraunhofer lines. The prism we are now using was made by Mr. J. A. Brashear of Pittsburgh, and when freshly polished, gives a spectrum not only filled with hundreds of Fraunhofer lines, but which shows distinctly the nickel lines between the D’s, and is probably the finest one ever produced from this material. Such measures on the collective heat of black bodies as those of Melloni and Tyndall have been made on large radiating sur- faces, like those of the Leslie cube, but in order to form a spec- trum, of this as of any other source, we must, of course, take only such a limited fraction of the side of the cube as is repre- sented by a narrow spectroscope slit; so that both from its minute amount and feeble intensity (even if we can pass it through a prism, to form a spectrum), it is absolutely inappreci- able, in anything like homogeneous portions, to the most deli- cate thermopile, and difficult of attack even by the bolometer. We have employed, as radiating surfaces, Leslie cubes cov- ered with lampblack and filled with boiling water or aniline, the former givigg a radiating surface of temperature of 100° C., the latter one of 178° C. and also cubes filled with freezing mixtures, with the latter of which Mr. F. W. Very, of this ob- servatory, conducted in the cold days of last March one series of measures in which the radiator was the bolometer itself, at a temperature of —2° C. and the source radiated to, a vessel filled with a mixture of salt and snow at a temperature of — 20° C., thus determining the distribution of energy in the spec- 6 SP. Langley—Observations on Invisible Heat-Spectra. trum of a surface below the freezing point of water. The Leslie cube used in these experiments was filled either with a freezing mixture, or with water kept gently boiling by a Bun- sen burner underneath; or again, when measurements from a source at an exactly determinable higher temperature were de- sired, with aniline, which has a boiling point of about 178° C. A condensing apparatus connected with the cube, in the Jatter ease prevented the escape of the aniline vapor. It was also found possible to keep the cube at any intermediate tempera- ture within sufficiently narrow limits by properly adjusting the flame. The apparatus is shown in Plate 2. Between the blackened side of the Leslie cube C and the spectrometer slit S, were in- terposed a large pasteboard screen (a) and a flat copper vessel (0) filled with broken ice, both pierced with apertures slightly larger than the slit, to allow the passage of the rays, and the exposures were made by withdrawing a third hollow screen (¢) made of copper and filled with ice, which cut off the radiation of the cube from the slit when it was in place. The train for forming the spectrum upon the bolometer face consisted of two rock-salt lenses L, L, and the rock-salt prism P. Each lens is 75™™ in diameter and 350™™ focus for visible rays. For the infra-red rays measured on, the focus is from one to two centimeters greater than this. The prism is made from an un- usually perfect piece of rock-salt, and is 64™™ on aside. Its constants having been fully given in this Journal for December, we will only repeat here for convenience that its refracting angle is 59° 57’ 54”, and that the indices of refraction for the Fraunhofer lines H,, 0,, A, are 1°56920, 1°54975, 1°53670, re- spectively, while that of 2, the farthest considerable absorption band in the infra-red of the solar heat spectrum is 1:5268, cor- responding to a known wave-length* of 1°82. With this train, composed entirely of rock-salt, and an ordinary eye-piece, the Fraunhofer lines are very distinctly visible in either sunlight or moonlight. The lenses, prism, slit and other parts of the train were mounted upon the large spectrometer (described in this Journal, xxv, 1883, and in the Mt. Whitney Report, Chapter x1). To illustrate the use of the apparatus, we give below in de- tail the observations of March 20, 1885, for getermining the form of the energy curve in the spectrum, of a Leslie cube at 178° C. The temperature of the room was —7° C., so that the excess of the temperature of the cube over that of the room was 185° C. The reading of the circle was made 0° 0’ 0” when the spec- trometer arms were in line, and the direct image of the slit fell * Given by a misprint 1:32 in the December number of this Journal. ty S. P. Langley— Observations on Invisible Heat-Spectra. 7 on the bolometer.. The prism was then placed on its table, the automatic minimum deviation apparatus connected, and the prism set to minimum deviation by a sodium flame held in front of the slit. The deviation of the ray falling upon the bolo- meter was then given directly by the circle reading to 10”. The bolometer used was 2™ wide, and consequently sub- tended an angle of about 20’in the spectrum. After adjusting the prism, the slit was opened to the same width. A secondary object of the experiment was the determination of the trans- mission of rock-salt in different parts of the spectrum, and for this purpose a plate of polished rock-salt, whose thickness was 9-1™™, was interposed at the slit, after each deflection obtained in the ordinary manner, the plate being allowed to remain in each case till the bolometer had registered the heat due to radiations from the salt itself, when the screen was withdrawn and the radiations from the Leslie cube allowed to pass through it. The results are given below in the form of a table. Deflection with Transmission Deviation. Deflection. rock-salt plate interposed. of plate. AOS Of 12 40 00 72 39 30 214 39 00 364 38 30 420 360 857 38 007 365 3% 30 269 251 933 37 00 196 36 630 137 122 891 36 00 96 35 30 62 63 1:02 35 00 48 34 30 29 2 931 34° 00 26°5 33 30 18 14 ‘778 33 00 10.5 The “transmission” of the plate of rock-salt (here uncor- rected for heat lost by reflection at the anterior surface) has been shown by subsequent experiments to very slightly diminish for extreme infra-red heat rays in the Leslie cube spec- trum; but to remain so nearly constant through the range of these experiments, as to show that the present approximate values need no correction on this account. More exact ones will be given in a subsequent memoir. The following series was then taken for fixing more accu- rately the position of the maximum: 8 SS. P. Langley—Observations on Invisible Heat-Spectra. Deviation. Deflection. 39° 00’ 375 38 50 406 38 40 430 38 30 428 She) PA) 414 58 10 401 38 00 371 From curves representing these observations, it was con- cluded that the maximum was at 38° 35’. It will be shown further on, how an attempt may be made to estimate the wave- lengths in these regions. Measurements were also made with surfaces of copper heated to much higher temperatures, and with the cube at different lower temperatures, for the purpose of determining whether the position of the maximum of the energy curve varies with the temperature, and if so, to determine if possible the relation. Experiments of this kind have been made by Mr. W. W. Jacques,* who found that “the distribution of heat in the spectrum of a solid or liquid source of radiation is nearly inde- pendent of the temperature of the source.” It was evident from the care with which Mr. Jacques’s experiments were con- ducted, that the shifting of the maximum must be slight and difficult of quantitative determination, but with the pure spec- trum and delicate heat-measuring apparatus at our command, it was thought possible that this might be effected. Accord- ingly, measurements similar to those just described were made with a radiating surface of lamp-blacked copper at the approxi- mate temperatures of 815° C., 525° OC. and 330° C., and with the Leslie cube at temperatures of 178° C., 100° C., 40° C., and — 20° C., the excess over the temperature of the room being in the latter cases respectively 185° C., 88° C., 46° C., and —18° C. In the last instance, the cube was colder than the bolom- eter strips, and the deflections obtained were negative; though small, they were distinctly measurable, the greatest being —12 divisions of the galvanometer scale.t We have in Plate 3 the curves representing the radiation from these sources, in which the abscissee are proportional to the indices of refraction in the rock-salt prism, but the ordinates only approximately so to the deflections of the galvanometer due to the heat at the corre- sponding points, since we are not here primarily concerned with the relation of the amounts of heat emitted to the temperatures * Distribution of heat in the spectra of various sources of radiation, by William W. Jacques, Ph.D., Proceedings of the American Academy. + The position of the maximum in the ice curve is indicated, but the curve itself is on this scale of ordinates, sensibly coincident with the straight line. (See Plate 1.) : . A S. P. Langley— Observations on Invisible Heat-Spectra. 9 of the sources of emission, but chiefly with the secondary effect of the progressive movement of the maximum which is clearly shown. Berelor observation | #2 u or aate \eruper [Approximate tempers: eyiation of maaxianan 1885. October 1, 815° C. 803° C. 39°:087 ome raS 525 505 39-03 on 6 330 318 39°01 a3: 330 310 39-00 September 26, | 300 275 38°42 March 20, 178 185 38°35 August 19, 179 152 38°35 March 20, | 119 126 38°25 October 7, 100 88 38-22 tf 3 | 39) 719 38°27 March 21, 40 46 38°00 ee oye | ZN) 118 37-40* It is to be observed of each of the curves in Plate 3, that though nearly all the avea is seen, yet that, owing to the exten- sion of the heat curve toward the right, the length shown is limited here by the size of the plate, whereas the extremity measured in each curve (except of course the solar one) does, in fact, correspond to an index of less than 1°45. We give above a table showing the dates of observation, the approxi- - mate temperatures of excess and the approximate deviations of the ordinate corresponding to the point of maximum heat in the (rock-salt) prismatic spectrum. We should observe that the higher temperatures are here only determined with an approximation sufficient to make it certain that there is a pro- gression in the direction of the shorter wave-lengths of the position of the maximum heat-ordinate corresponding to the temperature, as the latter rises. These results, both in the table and as represented in the plates, are given as preliminary, not as final, for we hope soon to be able to offer other and more exact ones, deduced from the heat spectra of bodies at all temperatures between that of melting platinum and melting ice. Weare entitled, however, even at, present, to draw the following conclusions, which are of special interest in connec- tion with the spectra of dark bodies, of which almost nothing has been hitherto known. (1) The heat represented by the areas of these curves is almost altogether of a character not observed in that of the sun, these wave-lengths, in general, not being transmissible by glass, which is comparatively permeable to the lowest solar * The positiou of the maximum in this latter case depends upon a single obser- vation of some delicacy and is liable to subsequent correction. 10 S&. P. Langley— Observations on Invisible Heat-Spectra. heat waves that penetrate our atmosphere.* To show this more clearly we have drawn the solar spectrum given by the rock-salt prism in its true position (though not in its trae amount) relatively to that of the heat curves cited. The max- imum of the latter lies in every case, it will be seen, far below the very lowest part of the solar invisible heat. (2) In spite of the compression of the infra-red by the prism, these heat curves extend almost indefinitely in the direction of the smaller indices, so far that we can, in fact, represent only a part of this extent in our plate. The measures already cited im case of the curve for the Leslie cube at 178°, for instance, show very measurable heat at a deviation of 33°, which corre- sponds to an index of refraction of 1°4511, while the smallest index given in the plate is 1-49. (5) An increase of temperature increases every ordinate, but not in like proportions, ordinates corresponding to the heat in the more refrangible parts always growing more rapidly than those for less refrangible heat. (4) As a necessary consequence of this, follows the (inde- pendently observed) fact of the progressive movement of the maximum ordinate toward the more refrangible end, as the temperature rises. (5) These prismatic curves are not symmetrical, the greater portion of the area in every case lying below the maximum, a. e., toward the greater wave-length, and the descent being always most abrupt on the more refrangible side. As the heat spectra from surfaces at the temperature of boil- ing water or melting ice are those to which the chief interest attaches, in connection with the temperature of the soil, and as these are not well shown on the same scale of ordinates with that of the red-hot copper, we give an independent representa- tion of these two in Plate 1, but upon the wave-length, not the prismatic scale. Their maxima of heat fall at points.in the normal spectrum which (as we explain later) are only approxi- mately determinate on éhis scale, but which are probably at least as low as the points (/) corresponding to the boiling water maximum, and (g) corresponding to the position of the maxi- mum ordinate in the spectrum of ice, at the melting point, or lower. No attempt is made in this plate to represent the rela- tive amounts of heat in the solar and Leslie cube curves, but only their positions on the wave-length scale; and here also it will be understood that the latter, curves really extend. far further to the right than the limits of the plate admit of show- ing them. * The distinctive character of these radiations is also well shown by the fact we have found that a thick film of lampblack, which is nearly as impervious to the dark solar heat as to light, transmits more than 50 per cent of the rays in question. Savin Langley—Observations on Invisible Heat-Spectra. 11 These observations, then, show a real though slight progression of the point of maximum heat toward the shorter wave-lengths as the temperature rises. ‘The position of the maximum ordinate of the lower curves is of course more difficult to determine, on ac- count of their flatness. The whole heat spectrum from most of these sources, it is interesting to note, passes through the prism at angles which the theories of our text books have heretofore pronounced impossible. he existence of these radiations, and the relative amounts of heat for each deviation, is certain, for these devia- tions are determined by the spectro-bolometer, in most cases with a probable error of less than a minute of arc; but when we pass to the next stage of our work, the determination of the corresponding wave-lengths, we cannot speak with such confi- dence. We have calculated the wave-lengths for some of the observations by means of Wiillner’s new formula,* 2 2 a n?>—1=—PA a ny where P, Q and 4, are constants, depending upon the nature of the refracting substance, to be determined by observation. This formula Willner founds on Helmholtz’s theory, but he has tested it by our own observations with the glass prism. We have found the calculated values to agree with similar ones obtained directly from the curve representing the relation be- between n and A for rock-salt, which is shown in Plate 4, by measurements on points whose wave-lengths were known from our prior observations up to about 23,000 of Angstrdm’s scale. Beyond this point we have continued the curve both by com- putation and by graphical extrapolation. We do not disguise from ourselves the danger of all extrapolations, although ours rest, it will be seen, on a wholly different basis from the ones depending on formulee derived from the visible spectrum alone, since our curve has been already followed by direct observa- tions until it is almost coincident with a straight line. Up to this point then (within the limits of error already elsewhere given) there is no doubt, and unless there is some utter change in the character of the curve, such as we have no reason to anticipate, a tangent from the last part will not differ very greatly from the immediate course of the curve itself, and will at any rate meet the axis of abscissze sooner than the curve can. If we assume then the prolongation of the curve to agree with this tangent, we evidently assume a minimum value for all the wave-lengths measured by it, and that is what we have done. We are not prepared yet to speak of these wave-leneth values as exactly determinate, and they are here given as first * Wiedemann’s Annalen, Band 33, p. 307. 12 A. Gray—Botancal Necrology of 1885. approximations. ‘They are indeed sufficiently startling, to make us inclined to proceed with caution; but, speaking with the reserves indicated by the conditions referred to, I may say that we have every reason to believe that the minimum wave- length assignable to the minimum ordinate of the heat curve, in the spectrum of a source whose temperature varies from 100° to 0° Centigrade, is a little less than 5, and a little over 6, and that these may be indefinitely greater. This refers, it will be remarked, only to the position of the maximum ordinate, while the extreme portions of tne curve measured on (corresponding to an index of 1-45) have probably at least three times this wave-length. I shall be better understood, perhaps, if I say that some of the heat radi- ated by the soil has probably a wave-length of over 150,000 of Angstro6m’s scale, or about twenty times the wave-length of the lowest visible line in the solar spectrum, as known to Fraun- hofer. These investigations are still going forward, and I hope soon to give more exact values. But I have presented the present ones, though imperfect, because they give us at least some knowledge of a region of which we are at present quite ignor- ant, and because they are thus I think of some interest both to the physicist and to the astronomer. ‘To the physicist, as show- ing that the wave-lengths which Newton measured to the gy tgp of an inch are so far from being the limits of nature’s scale, that the existence of measurable wave-lengths of something greater than yyy of an inch is rendered at least highly probable. To the astronomer, because we find that the heat radiated from the soil 1s of an almost totally different quality from that which ts received from the sun, so that the important processes by which the high surface temperature of the planet are maintained, can now be investigated with, we may hope, fruitful results in con- nection with the researches here described. I should not close this preliminary account without stating that I have in these observations been throughout and at every stage, indebted to Messrs. F. W. Very and J. EH. Keeler of this Observatory, for a collaboration without which it could not have appeared in its present form. Art. II. —Botanical Necrology of 1885; by ASA GRAY. CHARLES WRIGHT died on the 11th of August, at Wethers- field, Conn., at the home where he was born on the 29th of October, 1811, and where the early as well as the later years of his life were passed. He received his education in the grammar school of his native village and at Yale College, A. Gray—Botanical Necrology of 1885.’ ilps which he entered in 1831, graduating in 1835. His fondness for botany was developed while he was in college, although, so far as we can learn, he had no teacher. The opportunity of eritifying this predilection in an inviting region may have de- termined his acceptance, almost immediately after graduation, of an offer to teach in a private family at Natchez, Mississippi. Within a year pecuniary reverses of his employer terminated this engagement. At this time there was a flow of immigra- tion into Texas, then an independent republic; and Mr. Wright, joining in it, in the spring of 1837, made his way from the Mississippi to the Sabine, and over the border, chiefly on foot, botanizing as he went. Making his headquarters for two or three years at a place then called Zarvala, on the Neches, he occupied himself with land-surveying, explored the sur- rounding country, ‘‘ learned to dress deer-skins after. the manner of the Indians, and to make moccasins and leggins,” ‘‘ became a pretty fair deer-hunter,” and inured himself to the various hardships of a frontier life at that period. When the business of surveying fell off he took again to teaching; and, in the year 1844, he opened a botanical correspondence with the present writer, sending an interesting collection of the plants of Eastern Texas to Cambridge. In 1845 he went to Rutersville in Fayette County, and for a year or two he was a teacher in a so-called college at that place, or in private families there and at Austin, devoting all his leisure to his favorite avocation. In the summer of 1847-8 he had an opportunity of carrying his botanical explorations farther south and west. His friend Dr. Veitch, whom he had known in Hastern Texas, raised a company of volunteers for the Mexican war, then going on (Texas having been annexed to the United States), and gave Mr. Wright a position with moderate pay and light duties. This took him to Hagle Pass on the Mexican frontier, where he botanized on both sides of the river. He returned to the north in the autumn of that year, with his botanical collec- tions, and passed the ensuing winter in Connecticut and at Cambridge. In the spring of 1849, Mr. Wright returned to Texas, and, at the beginning of the summer, with some difficulty obtained leave to accompany the small body of U.S. troops which was sent across the unexplored country from San Antonio to El Paso on the Rio Grande. Notwithstanding some commenda- tory letters from Washington, no other assistance was afforded than the conveyance of his trunk and collecting paper. He made the whole journey on foot, boarded with one of the inesses of the transportation train, and endured many priva- tions and hardships. The return to the seaboard, in autumn, was by a rather more northerly route and under somewhat less + 14 ‘A. Gray—Botanical Necrology of 1885. untoward conditions. The interesting collection thus made first opened té&our knowledge the botany of the western part of Texas. It was published, as to the Polypetale and Com- posite, in the third volume of the Smithsonian Contributions to Knowledge, as Planie Wrightiane, part 1, in 1852. A year and more was then passed in the central portion of Texas, awaiting the opportunity for other distant explorations, supporting himself in part by teaching a small school. At length, in the spring of 1851, he joined the party under Col. Graham, one of the commissioners for surveying and determin- ing the United States and Mexican boundary from the Rio Grande to the Pacific, accepting a position partly as botanist, partly as one of the surveyors, which assured a comfortable maintenance and the wished-for opportunity for botanical ex- ploration in an untouched field. Attached only to Col. Gra- ham’s party, he returned with him without reaching farther . westward than about the middle of what is now the. territory of Arizona, and in the summer of 1852 le returned with his extensive collections to San Antonio, and thence to Saint Louis, to deliver his Cactacezee to Dr. Engelmann, and with the re- mainder to Cambridge. These collections were the basis of the second part of Plante Wrightiane, published in 1858, and, in connection with those of Dr. Parry, Professor Thurber and Dr- J. M. Bigelow, etc., of the Botany of the Mexican Boundary Survey, published in 1859. As Mr. Wright collected more largely than his associate botanists, and divided his collections into sets, his specimens are incorporated into a considerable number of herbaria, at home and abroad, and are the types of many new species and genera. No name is more largely com- memorated in the botany-of Texas, New Mexico, and Arizona than that of Charles Wright. It is an Acanthaceous genus of this district, of his own discovery, that bears the name of Carlo- wrightta. Surely no botanist ever better earned such scientific - remembrance by entire devotion, acute observation, severe ex- ertion, and perseverance under hardship and privation. Mr. Wright’s next expedition was made under more pleas- ant conditions. It was a long one, around the world, as botan- ist to the North Pacific Exploring Expedition, fitted out under Captain Ringgold, who was during the cruise succeeded by Commander John Rodgers. After passing the winter of 1852-3 at his home in Connecticut and at Cambridge, he joined this expedition in the spring, and sailed in the U.S. Ship Vin- cennes from Norfolk, Virginia, on the 11th of June. The col- lections made when touching at Madeira and Cape Verde were of course unimportant; but at Simon’s Bay, just round the Cape of Good Hope, a stay of six weeks resulted in a very considerable collection of about 800 species, within a small A. Gray—Botanical Necrology of 1885. 15. area, the Cape being wonderfully crowded with kinds of plants. The voyage was thence to Sydney and through the Corai Sea to Hongkong, which was reached about the middle of March, 1854. The collection of over 500 species of pheenogamous plants which was made during that spring and summer, upon this little island, and supplemented in the spring of 1855, was in part the basis of Bentham’s Flora Honkongensis. In the autumn of 1854, interesting collections were made on the Bonin and Loo Choo Islands, and later upon the islands between the latter and Japan. Still more extensive and important were the botanical collections made in Japan, especially those of the northern island, although the stay was brief. Also those made in Bering Straits, mainly on Kiene or Arakamtchetchene Island, on the verge of the polar sea, where the scientific members of the expedition passed the month of August and a part of Sep- tember, 1855. Reaching San Francisco in October, the season being unpropitious for botany, Mr. Wright was detached from the expedition, and came home by way of San Juan del Sur and Nicaragua, botanizing for a few weeks upon an island in the Lake, and thence by way of Greytown to New York. In the following autumn (of 1856) Mr. Wright began his prolific exploration of the botany of Cuba. Landing at San- tiago de Cuba, on the south-eastern part of the island, he passed the winter of 1856-7 and the greater part of the ensu- ing summer in that nearly virgin district, most hospitably entertained by his countryman Mr. George Bradford, and among the caffetals of the mountains by M. Lescaille, returning home with his rich collections early in the autumn. A year later he revisited Cuba, was again received by his devoted friends, extended his botanical explorations to the northern coast, and also farther westward, exchanging the dense virgin forest for open pine woods, like those of the Atlantic Southern States, stopping at various hatos or cattle-farms on his route, but reaching better accommodations at Bayamo, when his kind host, Dr. Don Manuel Yero, assisted him in making some profitable mountain excursions. In the winter and spring of 1861 he was again domiciled with the Lescailles at Monte Verde and at the other coffee-plantations of this kind family; and from thence he was able to extend his herborizations to the eastern coast from Baragoa to Cape Maysi. The next winter he made his way westward to near the center of the island, making headquarters at the sugar plantation of the hospitable Don Simon de Cardenas, thence visiting the Cienaga de Zapata, a great marshy tract toward the south coast. In early summer he transferred his indefatigable operations to the Vuedt-abajo, as it is called, or that part of Cuba westward of Habana, making his home at Balestena, a cattle-farm at the southern base of the 16 A. Gray— Botanical Necrology of 1885. mountains opposite Bahia Honda, where he was long most hos- pitably entertained by Don Jose Blain and Don F, A. Sauvalle. From thence he pushed his explorations nearly to the south- western extremity of the island at Cape San Antonio. In the summer of 1864 he came home with his large collections, re- maining there and at Cambridge for about a year. In the autumn of 1865, he went again and for the last time to Cuba, again traversed the Vuelt-abajo in various directions, proceeded by steamer to Trinidad and botanised in the moun- tains behind that town, thence by way of Santiago he revisited the scenes of his earlier explorations and the surviving friends who had efficiently promoted them. The oldest and best of them, the elder Lescaille, was now dead. In the month of July, 1867, our persevering explorer came home. Mr. Wright’s Cuban botanical collections, from time to time distributed into sets, with numbers, were acquired by several - of the principal herbaria,—the fullest sets of the Pheenogamous and vascular Cryptogamous plants, by the herbarium of Cam- bridge and by the late Professor Grisebach of Gottingen. Pro- fessor Grisebach was in these years engaged with his Flora of the British West Indies; so that he gladly undertook the de- termination of the plants of Cuba. They were accordingly mainly published in Grisebach’s two papers, Plante Wrightiane e Cuba Oriental, in the Memoirs of the American Academy of Arts and Sciences, 1860 and 1862, and in his Catalogus Plantarum Cubensium exhibens collectionem Wrighttanam aliasque minores ea Insula Cuba missas, an 8vo. volume, published at Leipsice in 1866. The latter work enumerates the Ferns and their allies: but those for the earlier part were published in 1860 by Pro- fessor Haton, in his Milces Wrightiane et Kendleriane, a paper in the eighth volume of the Memoirs of the American Acad- emy. The later collections are incompletely published in the Flora Cubana, a volume issued by F. A. Sauvalle at Habana, in 1878 and later,—a revision of Grisebach’s Catalogue (without the references, but with Spanish vernacular names attached) which was made by Mr. Wright, who added descriptions of a good many new species. ‘T'he only other direct publication by Mr. Wright is his Notes on Jussiea, in the tenth volume of the Linnean Society’s Journal. As to the lower Cryptogams, Mr. Wright’s very rich collections were distributed in sets and pub- lished by specialists; the Hungi by Berkeley and the late Dr. Curtis; the Muscz, by the late Mr. Sullivant, the Lichenes, by Professor Tuckerman in large part, and certain tribes quite recently by Miiller of Geneva. So Mr. Wright’s name is deeply impressed upon the botany of the Queen of the Antilles. There was a prospect that he might do some good work for the botany of San Domingo. For in 1871, a Government ves- A. Gray—Botanical Necrology of 1885. 17 sel was sent to make some exploration of that Island, and Mr. Wright went with it. It was in winter, the dry season, and the excursion across the country was hurried and unsatisfac- tory ; so the small collection made in this, his last distant botan- izing, was not of much account. Mr. Wright’s botanizing days were now essentially over. He made, indeed, a visit to the upper part of Georgia in the spring of 1875. But this was mainly for recuperation from the effects of a transient illness, and for seeing again a relative and companion of his youth from whom he had long been separated. A large part of several years was passed at Cambridge, taking a part of the work of the Gray Herbarium ; and one winter was passed at the Bussey Institution, in aiding his associate of the South Pacific cruise, Professor Storer. Of late there fell to bim the principal charge of the family at Wethersfield, consist- ing of a brother who had become an invalid, and of two sisters in feeble health, all unmarried and ageing serenely together. By degrees his own strength was sapped by some organic disease of the heart, which had given him serious warning; and on the eleventh of August he suddenly succumbed, while making his usual round at evening to look after the domestic animals of the homestead. Not returning when expected, he was sought for; the body was found as if in quiet repose, but the spirit had departed. * Mr. Wright was in person of low stature and well-knit frame, hardy rather than strong, scrupulously temperate, a man of simple ways, always modest and unpretending, but direct and downright in expression, most amiable, trusty, and religious. He accomplished a great amount of useful and excellent work for botany in the pure and simple love of it; and his memory is held in honorable and grateful remembrance by his surviving associates. GEORGE W. CurinTon died, at Albany, on the 7th of Sep- tember last, in the 78th year of his age. He was the son of DeWitt Clinton, one of the most distinguished governors, and ° the grand-nephew of George Clinton, the first governor of the State of New York. He was born on the 13th of April, 1807, whether in the city of New York or in the home on Long Island is uncertain; he became a student in Albany Academy in the year 1816, when his father entered upon his first tenure of office as governor, entered Hamilton College in 1821, was graduated in 1825, was led by his early scientific tastes to the study of medicine, which he pursued for a year ortwo. At least he attended two courses of lectures at the then flourish- ing country medical school at Fairfield, N. Y. There his ac- quaintance with Professor James Hadley further developed his Am. Jour. Sci.—Tuirp Series, Vou. XXXI, No. 181.—JAn:, 1886. 2 18 A. Gray—Botanical Necrology of 1885. fondness for chemistry and botany, as it did that of the writer of this notice a few years afterward. He also came under the instruction or companionship of Dr. Lewis C. Beck, a younger brother of his medical preceptor Dr. T. Romeyn Beck, attended a course of private lectures on Botany given by Dr. Wm. Tully, entered into correspondence with Rafinesque, Torrey, ete., and so bid fair to give himself to scientific studies, as we may suppose with the approval of his father, who, it is well known, had a decided scientific bent. But Governor Clinton’s death in February, 1828, wrought a change in his prospects and in the course of his life. Acting upon the advice of his father’s friend, Ambrose Spencer, the distinguished Chief Jus- tice of the State, he took up the study of law, attended the law-lectures of Judge Gould at Litchfield, Connecticut, and continued his studies at Canandaigua, N. Y., in the office of John C. Spencer, whose daughter he married. Admitted to the bar in 18381, he established himself at Buffalo in 1836, and practiced his profession most acceptably at the bar until the year 1854, when he became judge of the Superior Court of that city. This honorable position he continued to hold with entire approbation until January, 1878, when he retired under the provision of the constitution upon attaining the age of 70 years. Then he resumed the practice of the law for two or three years; but at length he took up his residence in Albany, partly for the more convenient rendering of his service asa Regent of the University of the State, and its Vice Chancellor, but mainly for investigating and editing the papers and writ- ings of his great uncle George Clinton. On the afternoon of the 7th of September he took an accustomed wall in the Rural Cemetery of Albany, and there he died, probably quite instan- taneously ; for when his body was found two or three hours later, some unwithered sprays of White Melilot, which he had gathered, were still clasped in his band. Judge Clinton’s professional life need not here be considered. I did not know him, but knew of him, as a botanist in his younger days. About the year 1860, after buying a botanical book for his daughter, the turning over its pages revived an almost forgotten delight; and when his attention was again given to the flowers he had long neglected, we soon came into correspondence. ‘I might have become a respectable naturalist,” he writes, ‘but was torn from it in my youth.... To become a botanist is now hopeless; I am, and must remain, a mere collector. But then I collect for my friends and for the Buffalo Society of the Natural Sciences. If I can please my _ friends and help the Society, it pleases me. I want it to suc- ceed. Money I cannot give it, and I give it all I can, the ben- efit of my example and pleasant labors.” An instructive and A. Gray—Botanical Necrology of 1885. 19 pleasant, and on his part a sprightly correspondence it has been ; and most ardent and successful were his efforts in the develop- ment of the Society of Natural Sciences over which he pre- sided, and especially of its herbarium which he founded. In the spring of 1864 he wrote: “To-morrow I believe I shall be able to mail you my Preliminary List of the Plants of Buffalo. And I demand that, immediately upon its reception, you write me, saying ‘pretty well for you.’ Ido feel gratified that Ihave at last made the mitiest mite of a contribution to science. I know how extremely minute it is. I would not be so exact- ing but for the fact that my letter-book is just full, and I want to commence a new one with a letter from you, I mean with a note from you: a letter is too ambitious.” As this modest Preliminary List exemplifies the beginning, so the full and critically prepared Catalogue of the Native and Naturalized Plants of the City of Buffalo and its Vicinity (pp. 215), published in 1882-38, marks the conclusion and shows the fruits of Judge Clinton’s work upon the flora of the district around Buffalo. This Catalogue was, indeed, prepared and published by his near friend and associate, Mr. Day, with a thoroughness and judgment which have been much com- mended. But the collection and elaboration of the materials, the critical determination of the species, and the preparation of the ‘‘ Clinton Herbarium,” as it is now appropriately called, were essentially his own work in the hore subsecive of a busy pro- fessional life. If during middle life, and while making his way in his chosen vocation he abandoned his early scientific avocation, he took it up again when he bad achieved a position which allowed some well-earned leisure, and he pursued it with an added zeal and energy and acumen, which should give his name a place among the botanical worthies,—to be remembered after those who knew and apprectated and loved him have passed°away. A little Scirpus specifically bears his name, but I never see the modest lihaceous plant of our northern woods, called Clintonia in honor of the father, without associ- ating it with the son. Judge Clinton’s contributions to the literature of the legal profession consisted mainly of his Digest of the Decisions of the Law and Equity Courts of the State of New York, in three stout volumes. But he was a not unfrequent and a fascinating writer in the newspapers of the city, an occasional lecturer upon historical as well as scientific topics, and an organ- izer or promoter of every good civic work. He was a per- son of marked and distinct individuality. It has been said of him that “he was not like anybody else, did not look like any- body else, and did not talk like anybody else.” But his ways and his conversation were peculiarly winning and delightful. 20 A. Gray—Botanical Necrology of 1885. Of a rather large family of children, four survive, two of them sons, and a goodly number of grandchildren. Epmonp Boissier died on the 25th of September, at his country residence in Canton Vaud, Switzerland, at the age of seventy-five years and three months. Having known him per- sonally almost from the beginning of his botanical career, which has been so honorable and distinguished, it is a melancholy satisfaction, as well as duty, to pay this passing tribute to his memory. ; Boissier came from one of those worthy families which were lost to France and gained to Geneva by the revocation of the Kdict of Nantes,—a family that has proved its talents and high character in more than one of its members. Madame the Coun- tess de Gasparin is a sister, next to him in age, and the two had their education very much incommon. He was born at Ge- neva, May 25, 1810, brought up and educated there, except that the summers were passed at his father’s place at Valeyres, which he in time inherited, and where his life was closed. From - his youth he was fond of natural history and of travel. It was not in his disposition, nor of the Genevese spirit of that day, to lead an aimless life; so, when he came to choose what may be ealled his profession, it was natural that, at Geneva, in the days of the elder De Candolle, he took to botany. He showed his great good sense by his early judicious choice of a field and by his unbroken devotion to it. ‘To the Mediterranean region, to Southern Spain, and the Orient most of his work relates. After a year or two of careful preparation he went to Spain, in 1837, explored especially Granada and the eastern Pyrenees, and between 1839 and 1845 brought out his Voyage Botanique dans le midi de I’ Espagne, in two large quarto volumes, the first of narrative and plates, 180 in number, the second of descrip- tive matter relating to the Granadan flora. Among the species he brought to light was the Abies Pinsapo, the beautiful fir-tree pow so well known in cultivation. His narrative, besides its botanical interest, is charming reading. In 1842, after his marriage to his cousin, of the de la Rive family, he traveled with his wife in Greece, Anatolia, Syria, and Kegypt. It was to his dear companion that he dedicated two of their joint discoveries, Omphalodes Lucilie and Chionodoxa Lucilice. In 1849 he experienced the great sorrow of his life in her death from typhoid fever, during a second journey in the south of Spain. Between 1842 and 1854 he pub- lished the first series of his Diagnoses Plantarum Orientalium Novarum, filling two volumes, and in 1855 the second series of almost equal extent; in 1848 he completed his monograph of the Plumbaginacee ; in 1862 he promptly finished his con- scientious elaboration of the great genus Huphorbia for DeCan- A. Gray—Botanical Necrology of 1885. — 21 dolle’s Prodromus, and in 1866 brought out the /cones Huphor- biarum, of 120 folio plates from outline drawings by Heyland. In 1861 he made a trip to Norway with his associate, Reuter. Not to mention other journeys, he was again in Spain and adja- cent countries in 1877, and lastly, in 1881, his eighth visit,—then in wretched health. Passing by scattered papers of his, we come to his great work, the flora Orientalis, in five octavo vol- umes. It comprehends Greece and Turkey up to Dalmatia and the Balkans; the Crimea; Egypt up to the first cataracts; North- ern Arabia down to the tropical line; Asia Minor, Armenia, Syria, and Mesopotamia; Turkestan up to 45° of latitude; Persia, Afghanistan, and Beloochistan—that is, up to the bor- ders of India. The lirst volume was published in 1867; the fifth, in 1884, brings the work down to its conclusion with the Pteridophytes ; and the manuscript for a supplementary vol- ume, for recent discoveries and some re-elaboration, was about half finished when he laid down his pen under an attack seem- ingly no worse than the many he had recovered from, but which now terminated his earthly life. It was a noble life, shadowed by an early bereavement, and in later years worn by painful disease,—the manly life of one who lived simply and wrought industriously where many oth- ers with his independent fortune would have lived idly and luxuriously; and he was no less a loyaland publie-spirited citi- zen. Upon an occasion when, long ago, we met him at Geneva, he had no time for botanical parlance, for he was doing duty in the ranks of the federal army. Later, at atime of commotion at Geneva, he helped to quell a revolutionary riot, and received a painful bayonet wound in the service. ‘True to his ancestry, he was a devoted Protestant Christian, a trusted member of the synod of the Free Church in Canton Vaud, where he lived when not in winter residence at Geneva, and where his assiduous attentions to the poor and the sick will be remembered. He was a man of fine presence, and till past middle life of much bodily vigor. Asa botanist he gave himself to systematic work only, for which he had a fine tact, and, like the school in which he was bred, perhaps a faculty for excessive discrimination. No man living knew the Europeo-Caucasian plants so well, or eould describe them better; and his herbarium must be, with possibly one rival, the most extensive and valuable private col- lection in Kurope. He loved living flowers as well, and rejoiced in his choice conservatory collections at Rivage, on the shores of the Leman, and in his well-stocked rock-works of alpine plants which adorn his grounds at Valeyres. A charming biographical notice by one who knew him well through his whole life, M. de Candolle, is contained in the Archives des Sciences of the Bibliothéque Universelle de Généve for October last. i rr 22 F. EB. Nipher—Surfaces of the Compound Pendulum. JOHANNES AUGUST CHRISTIAN ROEPER died on the 17th of March, 1884, at the age of eighty-four. He had been for some time the oldest botanist we know of, at least the oldest botani- eal author; for his first work, a monograpii of the German spe- cies of Huphorbia, was published in 1824. He was director of the Botanic Garden at Basle in 1828, when he published his classical paper De Organis Plantarum, and he may have been so in 1826, when he contributed to Seringe’s Melanges Botaniques his paper on the nature of flowers and of inflorescences, which first put the latter upon a scientific basis and essentially estab- lished the present nomenclature. He was botanical professor there in 18380, when he published his tract De Hloribus et Affini- tatibus Balsaminearum. In these essays he gave the promise of being one of the foremost morphological botanists of the age. Some time before the year 1840 he was translated to Rostock, where he held the botanical professorship for more than forty years, but without fulfilling the promise of his youth by additional contributions to the science of any considerable importance. There are, however, some articles from him in the Botanische Zeitung, and other German periodicals, the latest in the year 1859. In 1851 he was chosen a Foreign Member of the Linnean Society of London. We find no record of the place or time of his nativity. but we infer from a state- ment in the preface of his work on Huphorbia, which was pub- lished at Goettingen, that he was German, and not Swiss. He is said to have been most amiable, and of deep religious convic- tions. Art. Ill.—The SL tlie Surfaces of the Compound Pendu- lum ;* by Francis H. NIPHER. In discussing the compound pendulum, the statement is sometimes made, that particles near and below the axis of sus- pension are retarded, and that those near the bottom of the pendulum are accelerated by reason of their connection with the system. ‘The series of particles forming the axis of oscilla- tion are neither accelerated nor retarded. In a general way, so far as it concerns the time of a complete oscillation, this is all true, but it is not true in any compound pendulum ‘that the particles near the bottom continually exert a retarding effect upon the system. At any given instant, cer- tain particles in the system tend to diminish the actual accelera- * Read before the St. Louis Academy of Science, Oct. i9th, 1885. F. E.. Nipher—Surfaces of the Compound Pendulum. 28 tion, while others tend to increase it. These two tendencies always balance, although the value of each continually varies. These two groups of particles are separated by a surface, each particle of which has uo tendency to change the acceleration of the system, at that instant. The axis of oscillation always lies in this surface. On either side of this neutral surface there must be surfaces of equal tendency, those on one side having a plus, and those on the other side a minus sign. It is required to find the loci of these isodynamic surfaces at any given instant. This can be done by means of well known equations for the pendulum, which are first given. In fig. 1, let O represent the axis of oscillation, G the center of gravity, and S the axis of suspension. CallS G=K; S O=/, and let 7 be the distance of any element of mass dm from the axis 8. Let 6=the angle V SO, and a the angle between the lines 7 and 7, V S being the vertical plane containing the axis S. The entire mass of the pendulum may be supposed condensed on the vertical plane passing through G, and at right angles to the axes O and 8, each element of mass being supposed to be projected along a line parallel to those axes. The pendulum then becomes a thin plate of varying density, lying in the plane oi the paper as in fig. 1. This supposed condensation is really unnecessary in a rigid system, as the center of gravity G, and the element dm, may he in different planes, at right angles to the axis S without in any way changing the result. At any instant the linear acceleration of O is gsin @ and its angular acceleration is “ sin 6. This is also the angular accel- eration of every other particle in the system. ‘The linear accel- r at produce this acceleration on d m is eration of dm is therefore — g sin 6. The force required to Lr 6 H’=dm 7g sin 6. The moment of this force about S§ is Bd - g sin 6 (1) If the element dm were disconnected from the system, its 24. FL BE. Nipher—Surfaces of the Compound Pendulum. linear acceleration in falling as a simple pendulum would be g sin (+a) and the moment of the force required to produce this acceleration would be EB’; = dm rg sin (6+ a) (2) Subtracting (1) from (2), : 2 r(E"—F') = dmgr sin (6+) — dm gsin@ (3) The factor F’’—F’=d F is a force which must be impressed upon dm in excess of its tangential weight-component, in order to impart to the element its real acceleration at the given in- stant. ‘This force may be either positive or negative, the sign depending upon the position of d m, and the direction of swing. The integral of (8) for the entire system is necessarily zero, or, ne dmgr sin (+a) — a sin 0 J dm 7°=0. (4) & The first term is the moment of the weight of the system, referred to the plane VS.. The second integral is the moment of inertia I, referred to the axis 8. Hence, MgK sin 6 — 4 sin 01 —0, Where M represents the entire mass of the pendulum. ‘This gives the well known value of J. (fre z M.K The loci of the isodynamic lines in the dise pendulum are determined from (8), which may be put into the following form : rd ¥ g dm This expression represents the moment of the impressed force d F per unit of weight at any point determined by the values r,@ anda. Making this value constant.=a, it gives the condi- tion for an isodynamic line, which is therefore— 2 a=rsin 6+a) — = sin 6 (6) Let S be the origin of a system of rectangular codrdinates, « being the horizontal and y the vertical codrdinate of dm. Then =r sin (9+ a) — — sin 0 (5) as P=a2'+y’ and sin (O+a)=—, equation (6) becomes, l L 2 Vig ca aL ee = (1), b eas Sin 6 ENO e (“) For a fixed value of @ and a varying value of a, this is the equation of a series of concentric circles, the common center being on the horizontal through S at a distance — — from FE. Nipher—Surfaces of the Compound “Pendulum. 25 S. The radius of any circle is if l Ae Rs (2 ecg 8 V 5 Ae sin 6 a) ©) If a=o, we have the condition that the motion of a particle is unaffected by its connection with the system. The radius of of this neutral circle is therefore R’=3.- (9) Equation (7) then becomes the equation of a circle containing the two points O and §, and tangent to VS at the point S. When 8 O is horizontal, R’ becomes 4/ and when it is ver- tical R’= om. The position of the neutral circle for various values of @ is shown in fig. 2. For a pendulum of 39 inches, vibrating 2° on each side of the vertical, the radius of the neutral circle, or the distance of the common center varies between + 46 feet and to. S71 QV 2 Within the pendulum, the circle never departs materially from the tangent SV, particles on the one side tending always 26 «G. H. Williams—Peridotites near Peekskill, N. Y. to increase, while those on the other side tend to diminish the actual acceleration of the pendulum. In (8) the condition a= —.—— or a=$R’=d’, reduces the ra- 4 sin a dius to zero. This gives the value of a at the center of the wade L concentric circles. If the value of ano °8 deduced from (9) be substituted in (8) it becomes 1 a—+tR'— oT! This is the equation of a parabola, the position of whose vertex is given by the conditions Yiral ae = R’ B= Oy = gle the distance z being, of course, laid off at right angles to the plane of x, y. Revolving this parabola about its transverse axis, which is parallel to the axes O and S, the paraboloid of revolution obtained will represent the relation between @ and R for every point in the field. The changes which this surface undergoes during an oscillation of the pendulum, are very curious and interesting, but it is unnecessary to enlarge upon them here, further than to remark that the focus of the parab- oloid is always in the axis a, and its vertex is always in one of two right lines lying in a horizontal plane and making an angle of 80° with the axis a, and intersecting at S. These considerations are wholly independent of the maxi- mum amplitude of swing, and also of the geometry of the pen- dulum, excepting so far as it is involved in the distance J. The concentric circles which represent the isodynamic lines of the disc pendulum, are of course the right sections of coaxial cylinders, which represent the isodynamic surfaces of any com- pound pendulum. When @=0, these consecutive surfaces become a series of vertical and equidistant planes, as is shown by equation (6). R? (10) Art. 1V.—The Peridotites of the ‘‘ Cortiandt Series” on the Aludson River near Peekskill, N. Y. ; by Geo. H. WILLIAMS. IT is proposed in this paper to give a petrographical descrip- tion of the most basic members of that interesting group of massive rocks which occurs on the southern flank of the ocean Highlands about forty miles north of the city of New ork. The writer is under great obligations to Professor James D. G. H. Williams—Peridotites near Peekskill, N.Y. 27 Dana of New Haven, who called his attention to these rocks as affording promising material for petrographical study, and kindly volunteered to guide him in an excursion over them in the fall of 1883. A large number of specimens was subse- quently collected; but many other pressing duties have since retarded the progress of the work. This group of rocks, covering an area of not over twenty- five square miles, is composed of many and varied members. It is separated quite sharply from the gneisses, mica-schists and limestones which surround it, showing none of the gradual transitions into these rocks which Hermann Credner, in his description of this district written in 1865,* supposed to exist. Professor Dana, who encountered these rocks in the course of his studies of the limestone -belts of Westchester Co., N. Y., designated them as the “ Cortlandt Series,’{ from their being principally confined to the township of Cortlandt, and pub- lished a quite detailed account of their mode of occurrence and macroscopic characters. He at first thought that they might have resulted from the metamorphism of very ancient voleanic ashes stratified by water while the surrounding sedi- ments were being deposited.{ He has, however, since ex- pressed the opinion, based on several new and excellent eX po- sures, that at least the most basic members of the series are truly exotic, intrusive masses.$ Professor Dana has divided all the massive Cortlandt rocks into five classes according to the nature of their most import- ant non-feldspathic ingredient, viz: (A) Hornblendic (diorite), (B) Hypersthenic (norite), (C) Augitic (diabase and gabbro), (D) Biotitic (diorite) and (HK) Chrysolitic (peridotite): This classification may perhaps be advantageously followed, pro- vided it be remembered that no sharp line can be drawn be- tween the different groups; but that, on the contrary, every possible transition from each group ‘into every other occurs. Indeed I know of no other region of massive rocks so well calculated to show the transitions, both sudden and gradual, of one rock-type into another. The writer now proposes to describe petrographically the different types of the Cortlandt Series in succession, commenc- ing with the most basic; this may be followed by an account of the highly contorted and metamorphosed schists which occur around their edge, while any general conclusions regard- ing the origin and material of these rocks will be reserved to the last, Such a study will serve as a contribution to our knowledge * Zeitschrift der deutschen geologischen Gesellschaft, xvii, 1865, p. 390. + This Journal, ITI, xx, p. 194, Sept., 1880. + Ibid., II], xxii, p. 111, Aug., 1881. § Ibid., III, xxviii, p. 384, Nov., 1884. i Ibid., I, XX, p. 196, Sept., 1880. 28 G. HL. Williams—Peridotites near Peekskill, N. Y. of the little altered, ancient eruptive rocks of the United States; a knowledge necessary for any intelligent work on the very interesting question regarding the metamorphism of erup- tive masses which is now beginning to attract the attention of geologists. In the present paper only such of the Cortlandt rocks will be described as contain the mineral olivine. These are, for the most part, destitute of any considerable quantity of feldspar and belong therefore to the family of Peridotites; in some cases, however, by an increase in the amount of this constit- uent, they pass gradually into olivine-norites, olivine-gabbros and olivine-diorites. Curysouiric Rocks. Class I—Peridotite (Rosenbusch.) This class includes all massive, holocrystalline rocks of a granular structure, which are free from feldspar and contain, as their most characteristic constituent, the mineral olivine. The peridotites have been variously subdivided according to the other minerals which they contain, but for the present purpose it will be necessary to distinguish only two groups, in one of which hornblende, in the other pyroxene, is the most important ingredient. Itis not to be understood that the presence of one of these minerals in the least excludes the other; both are al- ways present, but in such varying proportions that it will be advantageous to designate which of the two, in a given case, plays the principal rdle. Both of these groups of peridotite occurring in the Cortlandt Series, are, in some respects, quite different from any which have been heretofore described. They everywhere grade into one another, and into their corre- sponding feldspathic equivalents. Of all the rocks occurring in the earth’s crust none are so subject to alteration as those composed largely of olivine. Nothing, therefore, can be better calculated to give an idea of the wonderful freshness of all the rocks near Peekskill than the fact that this very mineral is here frequently in an almost unchanged condition. The peridotites weather superficially into a reddish brown soil, but specimens taken from a short dis- tance below the surface show hardly more than the beginnings of alteration. The frequent polished and striated rock surfaces met with indicate that the great glacier was probably instru- mental in ploughing off and removing the more decomposed material, thus exposing the fresher rock below.* The distribution of the peridotites within the Cortlandt area is not a very extensive one. They are principally confined to *The freshness of these rocks is doubtless largely due to the relatively small amount of olivine which they contain. This, as will be shown in the sequel, is much less than that usually found in typical peridotites. pt ila G. H. Williams—Peridotites near Peekskill, N. ¥. 29 the northern half of Stony Point on the west side of the Hud- son River, and to the southern portion of Montrose Point on the east side of the river opposite Stony Point. LHven here, however, these rocks show a decided tendency to become feld- spathic. 1, HORNBLENDE PERIDOTITE. Hornblende Picrite (Bonney);* Hudsonite (Cohen).t The best locality for specimens of this type of peridotite is ut King’s Ferry, in the extreme northwest corner of Stony <= ,____1 Point, a small prominence on the west side of the Hudson, somewhat 8. W. of Verplanck. Across the western portion of this point the New York, West Shore and Buffalo Railroad have recently made some long and deep excavations which admira- bly expose the chrysolite rocks, together with their line of con- tact with the mica-diorite on the CKS.. Eee Wes2-2-- oF TRIASSIC LIMES TONE - CONGLOMERATE : : FhoteElectre. CoN¥}} north and with the mica-schist on the south. The road fol- lows the shore across the northern area of soda-granite (mica- * Qt. Jour. Geol. Soc., xxxvii, 1881, p. 137. Bonney’s name for this group of rocks is not a good one, inasmuch as pierile, by the sanction of long usage, indi- cates an aggregate of olivine and augite. Moreover Bonney considers the com- pact brown hornblende to have originated from the paramorphism of augite, a supposition which for the brown hornblende of the Cortlandt peridotites at least is wholly untenable. + This rock resembles very much the well known “ Schillerfels,”’ occurring near 380) «G. HX. Williams—Peridotites near Peekskill, NV. Y. diorite), as shown in the accompanying map; and exposes its eastern side in a high wall which is intersected by several fine erained dykes. It continues southward through the chrysolitic area and crosses the point in a deep cutting where the contorted mica-schists, their intersecting dykes and their contact with the peridotite, are all distinctly to be seen. In a small railroad filling near King’s Ferry on the north side of Stony Point, large quantities of the peridotite have been thrown out of tke adjoin- ing cutting and here many varieties may be collected. The most remarkable among these varieties is a dark green, at first sight apparently fine-grained rock, which, however, when held in the proper light, exhibits glistening, bronze-col- ored cleavage surfaces often measuring 8X4 inches. The re- flection from these surfaces is, however, not altogether con- tinuous, being interrupted by small rounded grains of a dull green mineral whose nature cannot be determined with the unaided eye but which the microscope shows to be olivine or serpentine. This is precisely the structure possessed by the ‘Schillers- path’’ or ‘‘ Bastit” of the Harz Mountains, which Professor Aug. Streng described as long ago as 1862.* It does not differ essentially from that of a feldspar crystal in graphic-granite whose cleavage surface is seen in reflected light to be inter- rupted by particles of uneven quartz. In fact this structure is so common in many massive rocks, especially in the more basic kinds, that I would venture to suggest the use of the term ‘« noicilitic ” (derived from the Greek zoextAog, mottled) for it. Professor Pumpelly has described the same phenomenon in the melaphyres of the Lake Superior region under the name of ‘“luster-moltlings,’ + a term adopted by Professor Irving for a similar structure which he found developed on a much larger the village of Schriesheim, a short distance north of Heidelberg in Baden, which has been elaborately described by Prof. E. Cohen (Benecke and Cohen: Geog- nostische Beschreibung der Umgegend von Heidelberg, 1881, pp. 141-148). This investigator regarded the large bronzy-looking crystals, enclosing smaller grains of the other constituents, as diallage. The same mineral is called ‘‘Schiller- spath ” by Fuchs and Bastite by Groth. Very recently however Cohen has re- vised his former determination and finds this mineral—as is the case in the Cortlandt rocks—to be hornblende. He therefore proposes to call this type of hornblende-olivine rocks *‘ Hudsonite,” on account of their extensive development on the Hudson River. (Neues Jahrbuch fiir Min., etc., 1885, II, p. 242.) This name has already been used by Beck (Mineralogy of New York, 1842) for a vari- ety of diallage occurring near Cornwall, N. Y., so that it would seem to the writer preferable, if a new name is necessary. to adopt the term ‘‘ Cortlandtite” for this class of rocks which play such an important réle in the “ Cortlandt Series.” *He says: ‘Charakteristish fiir den Schillerspath ist es, dass er tiberall yon Grundmasse durchsetzt wird, so dass sein deutlichster Blatter-Durchgang mit dunkeln, matten Fleckchen gesprenkelt ist.” (Neues Jahrbuch fir Min., Geol und Pal., 1862, p. 533). + Metasomatic development of the copper-bearing rocks of Lake Superior. Proce. Amer. Acad., vol. xiii, p. 260, 1878. G. H. Williams—Peridotites near Peekskill, N. Y. 31 scale in the coarse grained olivine-gabbros of the same district.* Professor M. EH. Wadsworth in a recent description of the Lherzolite from Presque Isle, Michigan, alludes to the same appearance and suggests that the reflecting mineral plays the same role in the peridotite that the iron does in the pallasites.+ In all cases heretofore described, the reflecting, bronzy min- eral appears to have been some variety of pyroxene—either augite, diallage or enstatite; in the peridotite from King’s Ferry, however, the glistening surfaces, as the microscope shows, are those of a brown hornblende.{ The individuals of this mineral are very large, being often four inches in diameter ; but, notwithstanding that they are so abundant as to be every- where in contact with each other, so full are they of inclusions _of the other constituents that they do not together make up one-half of the entire mass of the rock. (No. 90.)§ Another variety of this rock from the same locality, in which the reflecting surfaces of hornblende are considerably smaller, is much fresher than the one just described. (No. 95.) A macroscopical examination of these rocks is able to dis- close, in addition to the ingredients already mentioned, only frequent particles of magnetic pyrites (pyrrhotite) and glisten- ing flakes of a light green mica; a miéroscopical study of them, however, reveals much that is interesting. The fHornblende is undoubtedly the most important and characteristic constituent of this group of olivine rocks, for it is to this mineral that their peculiar habit is almost wholly due. That it is really hornblende which is present and not, as might be supposed by analogy with similar occurrences, some variety of pyroxene, is proven by the cleavage angle. Several measurements on a large Fuess reflection - goniometer gave values varying between 124° 15’ and 124° 50’ (calculated angle betweeen the prism (# P) faces for hornblende, 124° 30’). When examined under the microscope by transmitted light this mineral appears of a rich brown color, belonging to the * The Copper bearing Rocks of Lake Superior. Monographs of the U. S. Geol. Survey, vol. v, 1883, p. 42. + Lithological Studies. Part I. Mem. Mus. Comp. Zool. of Harvard College, vol. ix, p. 136, 1884. t Professor Bonney has recently described a peridotite from Swift’s Creek, Gipps’ Land, Australia, which very strongly resembles both the Schriesheim and the Stony Point rock. The large cleavage surfaces with an interrupted luster Bonney determined to be those of hornblende. This mineral had a green color and only a weak pleochroism, It is considered by the author to be possibly of secondary origin having been produced by the paramorphism of the pyroxene. (See Mineralogical Magazine, vol. vi, p. 54, July, 1884.) § The numbers given in connection with the different specimens are those of the collection of Cortlandt rocks belonging to the Johns Hopkins University. In case a letter is attached to a number, W. indicates that the specimen or section in question belongs to the writer’s private collection, while D. refers to sections loaned by Professor James D. Dana, for whose kindness in this respect the writer would express his deep obligation. 82 G. H. Williams—Peridotites near Peekskill, NV. Y. variety known as basaltic hornblende. The difference in ab- sorption between the ray vibrating parallel to the axis of great- est elasticity, a, and either of the others is very marked; but between the rays vibrating parallel to c and b a difference is hardly observable.* The color of the c ray is a dark chest- nut; that of the b ray the shghtest tinge lighter, while q is a light yellow. The absorption may be expressed by the formula c=b>>a.t In sections therefore which he in the zone # P #: OP a very strong change of color is observed when the stage is revolved over the polarizer. On the other hand sections nearly parallel to «Po or oP remain dark brown by a complete revolution. This accounts for the fact that apparently non- pleochroic hornblende often occurs in the same section with such as is strongly pleochroic. The difference depends only upon the direction in which the mineral is cut. The extinction angle in a section cut parallel to the clinopinacoid, measured against the cleavage lines (vertical axis), gave values varying between 9° and 10°. The inclusions in this hornblende are both numerous and characteristic. The most common are opaque black needles, ranging in size from the finest dust to about (08 mm. in length. The majority of these are arranged either parallel to the vertical axis or else so as to make an angle of about 45° with this. Others appear quite irregular in their position. More rarely small transparent crys- tals, the largest of which are 05 mm. long and ‘02 mm. broad, occur with the opaque needles. The nature of these could not be determined. They seemed, however, to possess a sharp crystal form, a high index of refraction and a parallel extinction. These are most frequently arranged with their longest axes inclined approximately 45° to the c. axis of the hornblende, or perpendicular to it. Still more rarely than these transparent crystals, the hornblende contains inclusions of thin brown plates similar to those which are so char- acteristic of hypersthene. All of these interpositions, of which the opaque black needles as a rule occur alone, show a tendency to concentration toward the center of the hornblende, leaving a border near the edge comparatively free from foreign substances. *In the mineral hornblende, } (axis of middle elasticity) coincides with the crystallographic axis b (orthodiagonal); ¢ (axis of least elasticity) agrees nearly . | . . . . . . . . . . with c (vertical axis), while a (axis of greatest elasticity and principal bisectrix) is situated in the plane of symmetry at right angles to c. + Vid F. Becke, Tschermak’s Min. und Petrog. Mitth., 1882, p. 235. G. H. Willeams—Peridotites near Peekskill, V. Y. 33 Often however they form irregular patches scattered like little clouds over the brown background.* ; The hornblende itself never shows any trace of crystalline form. It fills the irregular spaces between the other constitu- ents, a single individual often covering a space some inches — square. From its relations to the other minerals in the rock it is evident that it was the last to solidify, while the great size of the crystals would seem to indicate that the process of their formation went on very slowly. If, as seems probable, the portion of this rock now exposed cooled at a very considerable depth below the surface, the minerals like olivine, hypersthene and augite, which are commonly formed at comparatively high temperatures, might have separated out of the magma, leaving the remaining portion, which must have had almost exactly the composition of the brown hornblende, in a more or less pasty condition until the succession of a lower temperature, more in accordance with the amphibole than with the pyroxene arrangements of the molecules, finally allowed it to solidify in its present form. The well-known fact that the same molecule may crystallize at high temperatures as augite and at lower ones as hornblende, renders this a possible explanation of the curious structure of this rock. Itis equally applicable to such as contain no hornblende where bastite or diallage present the same appearance. Here also it is the youngest mineral (i.e the one formed at the lowest temperature) which encloses the others. In this case, however, complete solidification of the rock may have taken place before the temperature was suffi- ciently lowered to make hornblende a more stable form than pyroxene. The hornblende seems particularly subject to alteration, which is often far advanced before the olivine or the pyroxene _ are materially affected. The first change which the hornblende undergoes is a bleaching, accompanying which is the almost * The inclusions here described in hornblende, as well as those mentioned beyond as occurring in the olivine, are identical with those which Professor J. W. Judd, of London, has recently treated with considerable detail in his paper on the Tertiary Peridotites of the Western Islands of Scotland.. (Quarterly Journal of the Geological Society, vol. xli, p. 354, August, 1885.) This author considers all of the minute, indeterminable bodies which are so common in the feldspar, hypers- thene, diallage, hornblende and olivine of the more basic ancient eruptive rocks as secondary in their origin. He thinks that at the great depths at which these rocks were probably formed, the pressure imparted to the circulating waters such an increased solvent action that cavities having the form of negative crystals were produced in certain crystallographic planes, similar to the well-known ‘‘eetzfiguren.” Into these cavities he supposes certain ingredients, which had been leached out of the mineral or out of other minerals surrounding it, to have been deposited. To such a secondary process, which is almost always accom- panied by the development of a glistening, bronzy luster on the planes in which the negative crystal cavities have been formed, Professor Judd applies the name “ Schillerization.” (1. c., p. 383.) To the conclusion regarding the secondary formation of these well-known in- Am, Jour. Sci.—Tuirp Series, VoL. XXXI, No. 181.—Jan., 1886. 3 ~ 84. G. H. Williams—Peridotites near Peekskill, N. Y. total disappearance of the characteristic inclusions. The min- eral becomes nearly colorless and consequently nonpleochroic while retaining the compact structure and optical behavior of the unaltered portion. later there is developed, particularly around the edge of the hornblende, a bright, emerald green substance which on account of its lack of dichroism and very feeble action on polarized light may be regarded as chlorite. Next to the hornblende the most important constituent of this rock is the olivine, which is remarkable both for its fresh- ness and for its beautiful inclusions. It is present in rounded grains or in well defined crystals upon which the usual combin- ation of domes, prism and pinacoids may.be seen. These crys- tals vary from $ to 2 mm. in diameter. The mineral is quite colorless, with a high index of refraction, and is traversed by irregular cracks along which serpentinization may frequently be seen to have commenced, although in many sections there is hardly a trace of this alteration. The inclusions in this olivine are quite similar to those which have been described in the olivine-gabbro from the island of Mull on the west coast of Scotland by Prof. Zirkel* and by Prof. Cohen in the so-called Hypersthenite from Palma.t They are black and opaque, having generally the form of minute, rounded grains or long rods ar- clusions in the manner above described, the present writer would take exception on the following grounds :— Ist. It is by no means true that all crystals of the same mineral from the same locality, or even in the same specimen, always contain these inclusions in equal quantity. In the hypersthene of the Baltimore gabbros, for example, they are sometimes abundant, sometimes wholly wanting, and this is true even of indi- viduals occurring side by side in the same thin section. 2d. Professor Judd’s explanation is inconsistent with the frequent zonal ar- rangement of these inclusions. If they were formed subsequent to the solidifi- cation of their host, we should expect to find them uniformly distributed; on the contrary in the hornblende above described and in many feldspars they are con- centrated toward the center or grouped in regular zones. 5, 3d. It does not appear to be a fact that, as Professor Judd suggests, the minerals in which these inclusions are most abundant, are lighter in color or less strongly pleochroic than those without them. In sections of the Baltimore gabbros no difference could be observed by the writer between either the color or pleochroism of hypersthene crystals destitute of inclusions and such as were completely filled with them. 4th. The minerals in which the inclusions are most abundant are always ex- tremely fresh in their appearance. At the commencement of anything like alter- ation they are the first things to disappear. 5th. Many inelusions of this class do act upon polarized light, indicating that they belong to definitely crystallized species. To the writer there seems every reason to regard the indications which produce ‘“ schillerization’’ as original in their nature. They appear to be composed of substances extruded from the rest during the process of its crystallization as in- capable of forming a part of its chemical composition, not unlike the crystalliza- tion of certain impurities in limestone as various silicates, when the limestone undergoes metamorphism to marble. * Zeitschrift der deutschen geologischen Gesellschaft, xxiii, 1871, p. 59, Pl. IV, Fig. Il. Mikrosk. Beschaffenheit, p. 214. + Neues Jahrbuch fiir Min,, etc., 1876, p. 750. G. H. Williams—Peridotites near Peekskill, N. Y. 35 ranged parallel to one or more of the crystallographic axes of the olivine, although they are sometimes more irregular in their. distribution. Frequently these rods, instead of being straight, are variously bent and twisted, exhibiting the forms of trichites in obsidians. In such cases ‘they show a tendency to form elliptical groups resembling a fine arabesque, as figured by Zirkel. The same author has observed that while these incla- sions are very characteristic of the olivine of the older rocks, they are never found in that of the younger basalts. i could not see that those occurring in the Cortlandt peridotite were ever translucent as stated by Zirkel and Rosenbusch for other localities. There seems little doubt that they are com- posed of magnetite, since they are readily decomposed by acid, and since such grains of olivine as contain them in abundance are attracted by the magnet. Aside from the ordinary alteration of olivine to serpentine, which may be most instructively studied at every stage in the Cortlandt rocks, the most interesting phenomenon exhibited by this mineral is the beautiful development of reactionary rims or zones, wherever the olivine comes in contact with feldspar. This latter mineral is indeed no essential ingredient of the peridotites, but as already mentioned, they constantly show a tendency by its assumption to grade into olivine-gab- bros and olivine-norites. Wherever olivine comes in contact with feldspar, no matter how fresh both of the minerals may be, there is always present between them a double zone, the inner por- tion,nearest the olivine, being com- posed of square grains of nearly colorless pyroxene and the outer one of tufts of radiating actinolite needles of a beautiful bluish-green color and strongly pleochroic. Cer- tain slides in Professor Dana’s col- lection from Stony Point show this structure in great perfection, (see fig- ure). ‘The interior band of pyroxene is here 0:07 mm. wide; the exterior one 0:15 mm. The same phe- nomenon has been described by Tornebohm in the olivine-hyper- ites from Olme in Sweden* and is even more wonderfully devel- oped in a coarse grained olivine-norite from the south shore of Lake St. John, Prov. Quebec, Canada.t So constant is the de- pendence of this zone upon the contact of the olivine and the feldspar, that it must be in some way due to a reaction between the substance of these two minerals, the resultant amphibole and * Neues Jahrbuch fiir Min., ete., 1877, p. 383. + Vid. F. D. Adams, Am. Naturalist, Nov., 1885, p. 1087, aie ips. S6— Go 7: Williams—Peridotites near Peekskill, N. ¥. pyroxene having an intermediate composition. So sharply de- fined, however, are the crystals of this zone against the per- fectly fresh feldspar and olivine substance that it is difficult to conceive of them as produced after the rock had entirely solidi- fied. They may have been formed by a reaction between these- substances while at least one of them—the feldspar—was crys- tallizing, although in some cases the formation of the actinolite seems to have continued after this time. In any event, all traces of this border around the olivine disappears the instant this mineral comes in contact with any other constituent than the feldspar. The pyroxene constituent of the peridotite from King’s Ferry appears to be for most part hypersthene. It sometimes forms small irregular grains not larger than those of the olivine, but in other specimens it is present in individuals which are over a centimeter in length, enclosing the smaller grains of both oli- vine and hypersthene like the hornblende. In all forms it possesses all the ordinary characteristics of hypersthene, ex- cept that it is singularly free from the usual inclusions. Its pleochroism is very strong: @=a ray, red; b=b5 ray, yellow; { c=c ray, green. Its cleavage is well developed parallel to the prism (« P) and also still better parallel to the brachypina- coid (oP @). Its orthorhombic character is proven by its parallel extinction and the appearance of a bisectrix when such sections as are cut nearly perpendicular to the vertical axis are examined in converging polarized ight. A common, non-pleo- chroic augite, in which a diallage habit is frequently developed by the presence of a parting parallel to the orthopinacoid, is also often to be observed in this rock, although in many speci- mens it is altogether lacking. As this constituent increases in importance the rocks grade into those of the next group. The only remaining silicate which enters into the composi- tion of the hornblendic peridotites is the biotite. This mineral rarely retains its brown color. It is generally so completely bleached as strongly to resemble muscovite in thin sections. It is much bent and twisted, often having small lenses of cal- cite interposed between its lamella, like those figured by Dr. Hussak.* Aside from mere bleaching, the formation of the bright green, chloritic mineral, noticed as an alteration product of the hornblende, is also frequent. ‘he true character of this’ - mica is revealed by its very small axial angle—the hyperbolas - being hardly seen to open at all when cleavage pieces are ex- amined in polarized light—as well as by the fact that rarely sections may be found which have escaped the bleaching. * Anleitung zum Bestimmen der gesteinbildenden Mineralien, 1885, Taf. II, fig. 81. Gate Willioms— Peridotites near Peekskill, N. Y. 37 These have the characteristic color and dichroism of biotite and sometimes contain acicular inclusions resembling the needles of rutile described by the writer in biotite from the Black Forest.* Feidspar though frequently accessory, is never an important constituent of these rocks. Magnetite, aside from composing the tnelconet in the olivine above referred to, forms small grains which line the cracks in this mineral, and are especially abundant about its edge, where it is in contact with the brown hornblende. The large opaque grains scattered through the rock are almost all pyrrhotite, {magnetic pyrites (Fe,S,)); chromite or picotite were not ob- served ; another form of spinel however, pleonast, recognized by its dark green color and isotropic character, is not uncom- mon. This mineral is filled with thin opaque plates almost exactly like the inclusions in the well-known hercynite from Ronsperg in Bohemia. Apatite was hardly ever observed. 2. AUGITE PERIDOTITE. Picrite (Tschermak).t The true picrites of the Cortlandt Series are very closely related to the hornblende-peridotites just described. They are connected by a complete series of transitional stages in which the amount of hornblende becomes less and less, while a non- pleochroic augite, which under the microscope appears nearly colorless, is developed i in proportion. The best locality for the most typical picrite is near the east- ern bank of the river on the south side of Montrose Point. (No. 62). In this rock the brown hornblende, although still present in the form above described, is reduced both in amount and in the size of the individuals, while the augite reaches its maximum development. Montrose Point rises on the western side of the basin in which most of the Crugers brick-yards are situated, as a rather abrupt rocky wall. This is generally covered with a reddish, earthy deposit, due to the oxidation of the iron in the basic an nerielle of which it is composed. The rock, of which very fresh and unaltered specimens may be ob- tained near the river bank, is of a dark green color and of an even grain of medium coarseness. When examined with the unaided eye its most prominent feature is the glistening, black cleavage surfaces of hornblende. Small grains of magnetic pyrites and reddish spots indicating the former presence ‘of an olivine crystal are abundant. In a thin section under the microscope the hornblende, in spite of its prominence in the hand-specimen, is seen to be sub- * Neues Jahrbuch fiir Min., Geol. und Pal., II. Beilage—Bd., p. 617. + Sitzungsber. d. k. Akad. in Wien., 1866. Bd, xl, p. 113. 388 -G. H. Williams—Peridotites near Peekskill, N. Y. ordinate to the pyroxene. This mineral is chiefly represented by a nearly colorless augite, which frequently assumes the habit of diallage by the development of a pronounced part- ing parallel to the orthopinacoid. In spite of this, however, the inclusions so characteristic of diallage are, in all of this monoclinic pyroxene, almost wholly absent. This mineral can of course show no pleochroism when it is so nearly colorless. Twinning lamelle parallel to the orthopinacoid are frequent, their boundary being often visible in ordinary light as a sharp line. The extinction angle in prismatic sections is in some instances as great as 40°. Cleavage fragments parallel to the orthopinacoid show in converged polarized light a single opti- cal axis which remains nearly stationary in the field when the stage of the microscope is revolved. Hypersthene, in all respects identical with that described as occurring in the hornblende peridotites, is common, but in no instance is it as abundant as the diallage. Very interesting in- stances of the parallel growth of these two minerals were ob- served where the orthopinacoids of both lie in the same plane. In some cases no line of demarcation could be seen between them, although the pleochroism of the hypersthene easily dis- tinguished it from the diallage. A crystal of the latter mineral looks as though it had become red and pleochroic at one extrem- ity or the other; but between crossed nicols the orthorhombic character of this pleochroic portion is very apparent and in great contrast with the high extinction angle of the diallage. The hornblende is likewise quite identical with that already described. It is, however, much reduced in amount and in the size of the individuals. In the abundance of its inclusions it forms a contrast to both of the pyroxenic constituents. The olivine shows no peculiarities which have not been already noted. It is not present in large amount but forms comparatively sharply defined crystals, scattered at intervals among the other constituents. It is often extremely fresh but in other cases completely changed to a yellow, isotropic ser- pentine. Considerable magnetite is readily extracted from the powder of this rock with a magnet. Neither apatite nor feldspar were observed in the sections of the Montrose Point rock. Another rock almost identical with the one just described from Montrose Point was collected about 135 yards west of Munger’s near Montrose station on the N. Y.C. R. R. (No. 46.)* Still another specimen (No. 54), which belongs to this type © was obtained near the house of Mr. Butler, on the road leading from Montrose Point to Montrose Station. It represents a * Mentioned by Prof, Dana in this Journal, Sept., 1880, at the foot of page 217. G. H. Williams—Peridotites near Peekskill, VEG ao member of the extremely interesting section exposed here for 350 feet and described by Professor Dana in his paper on the Limestone belts of Westchester County.* The rocks here vary considerably in their mineralogical composition at different points. They are for the most part quite massive but not in- frequently they exhibit signs of a schistose structure. ‘This Professor Dana was inclined to attribute to only partially ob- literated stratification planes; but a microscopic study of the rocks in question shows most conclusively that the structure is one which was secondarily developed in massive rocks by the action of great pressure. Scarcely any specimen is better cal- culated to show the effects of such action on the minute inter- nal structure than the above mentioned No. 54. The minerals present are diallage, hypersthene, brown hornblende and a little olivine. The principal constituent is diallage in large rounded individuals which are frequently twinned and always possessed of that peculiar, finely striated (almost fibrous) appearance, which is well known to be the result of pressure.t These diallage crystals are often bent and, no matter what may be their crystallographic orientation, it can be seen- that for all the pressure acted from one constant direction. Around these diallage individuals, and occasional hypersthene crystals which have been subjected to like influences, extend finely granular, curving bands of secondary pyroxene and brown hornblende. This granular aggregate encloses the large, rounded and bent pyroxene crystals like a groundmass and produces a structure similar to that seen on a larger scale in the “‘augen-gneiss.”{ Such fine-grained aggregates of secondary minerals enclosing the remains of larger original crystals have been admirably described and illustrated by Professor J. Lehmann§ in the ‘“ Augen-gneisses, granulites and ‘“ Flaser-gabbros” of Saxony and by Professor K. A. Lossen|| in the metamorphosed diabases of the Harz Mountains. ; It is a fact not without significance in the case before us that brown hornblende is a very abundant constituent of the second- ary groundmass while it appears to be lacking among the origi- nal constituents, although the larger individuals of diallage appear in some cases to be passing into it by paramorphism. Two sections of Professor Dana’s collection marked St. 8 (D) * This Journal, Sept., 1880, p. 218. + Vid. O. Miigge, Neues Jahrbuch fiir Min., Geol. u. Pal., 1883, i, p. 84, and van Werveke, ib., ii, p. 99. ; t For the German term for this structure: ‘“flaserige or mikroflaserige Struktur” there seems to be no exact English equivalent. It is common in the gneisses and is sometimes called lenticular structure. The term “ flaser-structure” might be adopted for it from the German. = Untersuchungen tiber die Entstehung der altkrystallinischen Schiefergesteine. Bonn, 1884. || Jahrbuch der kon. preuss. geologischen Landesanstalt fiir 1883, p. 619. oe ee 40 G. H. Williams—Peridotites near Peekskill, N. ¥. and St. 6 (D) belong to this class of picrites. A chemical analy- sis of the rock (No. 62) from the south side of Montrose Point was made by Mr. W. H. Emerson in the laboratory of the Johns Hopkins University with the following result :— DiOi ys 2s) Cake Sees eS eae 47°41 AYO hee eee eee 6°39 Fe: 23a eee aa eee 7°06 BeOS 20 RR Te eee 4°80 CaO Sees Wee Soe yy een 14°32 Mo Oise coats fie reiee 15°34 INEIOK ce Sie als ee ‘69 (determined by difference) REQ EE AGO Lad OR LENT 1:40 EDOM EEDA ieee 2°10 ee yee ENR CR ERD inte “49 100°00 Specific gravity = 3-30 at 15° C. f The sulphur may be referred to pyrrhotite. The high specific gravity and the percentage of ferric iron present indicate a con- siderable amount of magnetite. The almost equal quantities of lime and magnesia prove that neither hypersthene nor olivine can be largely represented among the constituents. The silica will be seen at once to be too high for a typical peridotite. In fact all the most basic rocks of the Cortlandt Series which have come under the writer’s notice are too acid to be classed as representative olivine-rocks. This manifests itself, as in the rocks here described, in the relatively small amount of olivine associated with the pyroxenic constituents or in their tendency to develop feldspar and so form transitions to olivine-gabbros and norites. A rock, which is quite common on the northern side of Stony Point and also to be met with at several localities in the town- ship of Cortlandt, possesses a composition intermediate between the hornblende-peridotite and the picrite. The groundmass of this rock is a moderately fine-grained, gray colored aggregate composed ; principally of diallage with some = Z40\ hypersthene and olivine. It corre- 2 Ee & S54 sponds quite closely to the picrite. et. 6 +5] Imbedded in thisare sharply formed eras hs S7jIV Wa crystals of black hornblende from one to two centimeters in diameter. ay es These are short prismatic in shape,