be distinguished amid the black mass that surrounded them; the lines near C and C' or y of Brewster were sharp and clear. On nearing India another change took place; the blue continued to be absorbed, til at sunrise the spectrum could hardly be seen beyond F, but the blue green became very bright, and the dark bands between and F very distinct, the lines commencing at 1825 Kirchhoff especially attracted notice, standing out sharp and distinct, so as at first to be mistaken for F: those nearer F at 1890 K showed as a clear broad band, but not nearly so black as 1825. I am not prepared to give an explanation of this phenomenon, but will remark that when the sun rose clear and free from clouds the aqueous bands to D were less distinct, while the atmospheric bands from D to E were clear and sharp, and those beyond b remarkably so. But if the sun rose among clouds, these were generally tinted with a golden yellow, changing afterwards to a rose or red colour, and, as might be expected, the lines from B to D and just beyond D, were well defined, whilst from E to near F the spectrum was not so clear. After this the duties of preparing the instruments for the eclipse prevented my taking any observations, as most of our work was done in the early morning. But after the eclipse, whilst on the Neilgherry Hills, 6,000 feet above the sea, I had an opportunity of finding that the strong line at 1825 had nearly faded away. The weather was then fine, but misty. A few days after, on going down the Ghauts to Bombay, I was struck with the blue colour of the mist that was hanging about the valleys, and I examined it with the spectroscope; the blue extended much farther than usual, and the lines between 6 and F were again distinct. On the passage home the same results were obtained as on going out; but as I had a much smaller spectroscope I could not make the observations with the same accuracy as before. When passing up the Red Sea the absorption was evident at both ends of the spectrum, and the mountains were of the same beautiful purple colour that I had noticed before. From Alexandria to Southampton we had very bad weather, constant gales, making it difficult to observe. But I got the following results: With a cloudy sky at sunrise, and appearance of wet weather, the bands from B to beyond D (8 of Brewster) were strong, whilst the blue end of the spectrum was greatly absorbed, and the lines from 6 to F were less distinct; this was reversed with clear weather. As we gained higher latitudes, the blue end of the spectrum lengthened out, and the bands beyond F, particularly about 2330 K, became distinct, while the bands 1825 K and 1890 K gradually faded, and now their intensity is not one-fourth of what I observed it in the Indian Ocean. These observations are very imperfect, but I hope, if I can get the instruments, to carry out a more perfect system of observation, feeling sure that it is a subject worthy of great consideration in meteorology, especially when taken in connection with the temperature and pressure of the atmosphere and the state of the weather. Shanklin, Feb. 5 J. P. MACLEAR PROF. AGASSIZ'S EXPEDITION T is probable that I may have been anticipated, as regards part of the present communication. If not, I believe that many of your readers will be glad to learn the objects with which Prof. Agassiz has started, with Count Pourtales and a distinguished band of skilled ob servers, on a scientific expedition in the United States' surveying ship Hassler, and to receive a brief account of what he has already done at St. Thomas and Barbados, at which places he was obliged to touch, in consequence of defects in the vessel or her machinery. The Professor's chief objects are stated in a letter from himself to Prof. Peirce, the Superintendent of the U.S. Coast Survey. (See NATURE, vol. V., p. 194.) The Expedition was detained some days at St. Thomas, and the time of the Professor and his assistants was devoted chiefly to the collection and preparation of fishes, with a view to the study of the brain, and the breathing and digestive organs. Several boxes full, preserved in alcohol, were at once shipped to the United States, as the firstfruits of the Expedition. The party arrived at Barbados on December 26, and spent four days there. The first two were devoted by the Professor to examining and studying the large collection of West Indian shells, marine and terrestrial, of corals, sponges, crustacea, and semi-fossil shells of the island, made by the Governor, Mr. Rawson. Of the marire series he wrote in the following terms to Mr. J. G. Anthony, the Curator of the Harvard Museum :-"I am having high carnival. I have found here what I did not expect to find anywhere in the world-a collection of shells in which the young are put up with as much care as the adult, and extensive series of specimens show the whole range of changes of the species, from the formation of the nucleus to the adult." He was particularly struck with the now unique specimen of Holopus, lately procured by Mr. Rawson, which was described by Dr. J. E. Gray in the December number of the "Annals of Natural History," and named by him, from a drawing, H. Rawsoni, but which Agassiz, who had seen the specimen of D'Orbigny in Paris, before it disappeared, considers to be a normal specimen of H. Ranzii, which had only four, instead of five arms. Count Pourtales recognised among the corals several similar to those which he had obtained by dredging in or near the Gulf Stream, and described in the latest No. (4) of the "Illustrated Catalogue of the Museum of Comparative Zoology at Harvard College," the presence of which on the coast of Barbados serves to indicate the close similarity of submarine life in those two distant localities. The next two days, or rather the night of the next, and the greater part of the following day, were spent in dredging in the neighbourhood, in a depth of 60 to 120 fathoms, about a mile from the shore, whence Mr. Rawson has procured his fine specimens of Pentacrinus Mülleri. The Holopus was found on the opposite side of the island. The results were beyond the expectations, or even the hopes, of the most sanguine of the party. Only dead fragments of the Pentacrinus were obtained, but among the abundant spoils were four specimens of a new genus of Crinoid, without arms on the stem, (like Rhizocrinus ?) which remained alive, with the arms in motion, until noon on the following day, under the excited observation of the party. A number of deep-sea corals, alive, crustacea, sea urchins of new species, star fish, sponges, crystalline, jurassic, and corallines, &c., and a rich harvest of shells, were obtained. Among these was a splendid live specimen of Pleurotomaria Quoyana, F and B, of which genus Chenu writes that only one living species, and of that only one specimen, is known. The animal exhibited remarkable affinities, and the artist accompanying the expedition was able to take several sketches of it. A large Oniscia, shaped like O. cancellata Sow. but with an orange inner lip (0. Dennisoni?), some specimens of Phorus Indicus Gmel., a magnificent new species of Latiaxis, with many exquisite specimens of Pleurotoma, Fusus, Murex, Scalaria, and three or four of Pedicularia sicula Sw., with innumerable Pteropods and Terebratuline, rewarded these "burglars of the deep." The Professor was delighted, and it was with reluctance he abandoned so rich a field in order to secure his passing through the Straits of Magellan at a right season. Barbados, January 26 R. W. R. THE ETHNOLOGY AND SPIRITUALISM HE Academy of February 15 contains a review. by Mr. A. R. Wallace, of my "Primitive Culture," where he raises a point on which I wish to make some further observations; but inasmuch as the form of publication of that journal adapts it rather to criticism than to correspondence, I ask leave to change the venue, and make my remarks in the columns of NATURE. In "Primitive Culture" (Vol. i., pp. 279-84), I have given an account of the widespread popular belief in were-wolves," including under this heading the analogous belief in man-hyænas, man-tigers, &c. According to this superstition, certain human beings are considered to be temporarily transformed into wolves, hyenas, or tigers, and in these shapes to go about preying on mankind. While expressing an opinion that "the origin of this idea is by no means sufficiently explained," I have offered two suggestions as bearing on its prevalence in the world: first, that such notions are consistent with the familiar doctrines of the lower culture as to transmigration of souls and transformation of bodies; second, that certain insane persons do actually suffer under the delusion that this transformation (the idea of which popular belief has put into their minds) has really happened to themselves, and they prowl about like wild beasts accordingly. Mr. Wallace disapproves of this treatment of the subject, and propounds a view of his own, as follows: "A recognition of the now well-established phenomena of mesmerism would have enabled Mr. Tylor to give a far more rational explanation of were-wolves and analogous beliefs than he offers us. Were-wolves were probably men who had exceptional power of acting upon certain sensitive individuals, and could make them, when so acted upon, believe they saw what the mesmeriser pleased; and who used this power for bad purposes. This will explain most of the alleged facts, without resorting to the short and easy method of rejecting them as the results of mere morbid imagination and gross credulity." Let me now first observe that Mr. Wallace's explanation does not supersede my suggestions; indeed, he meets neither of the points which I endeavour, however tentatively, to deal with. He offers nothing like a reason why knavish sorcerers in districts of Europe, Asia, Africa, and America should have all hit upon the device of imposing the same peculiar delusion upon their dupes; nor does he account for the fact, vouched for by satisfactory evidence, that in certain cases the supposed were-wolf is himself utterly persuaded of the reality of his own transformation, and goes to execution believing in his offence. The proofs are, think, convincing, here as elsewhere in the history of magic, that sorcerers were originally and still are usually more or less believers in their own magical pretensions-though very many used and use fraudulent means to enhance their supposed powers; and some, who may be reckoned among the vilest of the human race, are simply professional impostors. Yet Mr. Wallace's suggestion, though it does not do away with the need of mine, seems to me valuable as a well-directed attempt to explain a part of the matter left untouched by me. His theory that a were-wolf may be a person possessed of the pecu liar faculty exerted by mesmerists, of making others delusively imagine that they see and hear what in fact does not happen, is a theory at any rate plausible, and possibly on the track of explaining much of the power belonging to sorcerers, savage and other. (I may remark incidentally that the power of mesmerists in producing anasthesia and working on the imagination of their patients has never been contradicted by me.) Now, without committing myself to Mr. Wallace's idea, beyond saying that it is plausible and worth pursuing, I proceed to apply it somewhat farther. Granting that a were-wolf, in virtue of being a person capable of exerting mesmeric influence, can delude people, and even assemblies of people, into fancying that they perceive monstrous unrealities, the question arises, Was any one with this were-wolf-faculty present in the room when Mrs. Guppy made her celebrated aërostatic entrance? Is Mr. D. D. Home a werewolf? Is a professional "medium" usually or ever a person who has the power of acting on the minds of sensitive spectators, so as to make them believe they see what he pleases? Pursuing this subject yet a step farther, I have now to call Mr. Wallace's attention to an interesting fact. The sorcerers of the Abipones of South America, who by mere roaring within their tents threw the credulous savages into agonies of panic terror, caused by vivid belief that tigerspots were in the act of coming on their (the sorcerers') bodies, that their nails were growing into claws, that they were actually transforming themselves into tigers, deadly though invisible-these sorcerers were actually the professional spiritualistic mediums of the tribe, part of whose business it was to hold intercourse with the spirits of the dead, causing them to appear visibly, or carrying on audible dialogues with them behind a curtain. Mr. Wallace, as the most eminent scientific man who has taken up what are known as modern "spiritualistic doctrines," no doubt has the ear of all who hold these doctrines. I think it may bring about investigations leading to valuable results if Mr. Wallace will inform spiritualists with the weight of his authority that he believes in the existence of a class of men who, in his words, have exceptional power of acting upon certain sensitive individuals, and can make them, when so acted upon, believe they see what the mesmeriser pleases, and who use this power for bad purposes. With reference to other parts of Mr. Wallace's review of my work, I have to thank him for several valuable comments, while, at the same time, I venture to express an opinion that some of his objections to my ethnological treatment of spiritualism are unreasonable, and especially I wonder that so serious a student of natural science should make it a ground of complaint against me that in treating of difficult and important problems I consider it necessary to bring forward copious and widely distributed evidence. But rejoinders to reviews are seldom desirable in themselves, and my justification for the present note lies in the importance of drawing attention to a matter worth considering by persons on both sides of the spiritualistic controversy. E. B. TYLOR DREDGING EXPEDITIONS THE occasion of an American Dredging Expedition recently starting, leads us to make the following remarks on such Expeditions in general, more especially upon one whose programme has lately come to our ears. England has perhaps of all countries done the most for dredging. We have only to point to such names as Forbes, Ball, McAndrew, Wallich, Jeffreys, Wyville Thomson, and Carpenter, as among the landmarks in the cause. Indeed, for many years coast dredging has been a popular amusement with the marine naturalist and collector, and many a prize has been in this manner turned up. In 1868 Messrs. Carpenter, Thomson, and Jeffreys were fortunate enough to obtain the use, free of expense, of a Government steamer, and, armed with a substantial grant from the Royal Society, tried their luck in the deep sea. The following year the Government again gave them the use of a vessel, and the Royal Society a further grant of 2007. Again in 1870 they went out at the country's expense. The great and important results obtained during these cruises are pretty well known to the scientific world, and it is unnecessary to repeat them here. In the year last mentioned an unheard-of circumstance took place. An English yachtsman, Mr. Marshall Hall, not only gave up the use of his yacht for the summer in the cause of Science, but bore nearly the whole expense of the cruise himself. The naturalist who accompanied them was Mr. Kent, of the British Museum, a man comparatively unknown before that time; and this was, perhaps, the reason why the Royal Society could only afford to give £50 towards the expense of apparatus, &c. As a natural consequence, the expedition was considerably crippled for want of proper gear, and they were unable to attempt deep-sea work. It is too rare for persons who are blessed with means to assist Science in any way, and when such an act of generosity does take place, it ought not to be forgotten on the part of the scientific public. Yet it is rumoured that a similar expedition to Morocco and Madeira, which Mr. Marshall Hall is arranging for the spring, is likely to be received with some coldness by some influential members of the scientific brotherhood. We sincerely hope that the rumour is incorrect. It appears that Mr. Marshall Hall proposes to be absent from England for between three and four months; and, besides the natural history, to investigate, as far as possible, certain chemical and physical questions concerning the deep sea and its currents in the neighbourhood of the above-mentioned places. He is taking with him a young naturalist, Mr. P. T. Abraham, B.A., B.Sc., lately from Dublin, at which University he came out first in natural science honours, and where he has gained a high reputation for zoological knowledge. It is also probable that another naturalist will make up the staff. These gentlemen intend to give, besides the use of the yacht, 150l. or so as much as they are able. The remaining 250% for the total cost of the expedition could not amount to much less than 400/., when the items of gear, apparatus, outfit, and maintenance for such a time are taken into consideration-they hope to obtain in the form of grants from the learned societies. We feel sure that the Royal Society will be among the first to endow the work out of the fund placed at their disposal by the Government, and the best friends of Biology may wish that they had more frequent opportunities afforded them of assisting in researches in which it is fitting that in the first instance a private individual should come forward. It is possible even that other societies may be induced to help if they have funds at their disposal. Among such societies we may mention the Zoological Society, which contains on its roll the names of men of the first rank in every department of zoology. It is true that a great portion of the funds are expended in the direction of the higher vertebrates, and that the lower animals do not receive the attention they may deserve; but still, it must be remembered that the great object of the society is the popularisation of natural history. We hope that the Norna's will not be the only dredging excursion starting from British waters this year. The field that has been so ably opened up by Dr. Carpenter and his colleagues ought not to be allowed to slip away altogether from the hands of Englishmen. We know too well that other nations are not backward in following up and eclipsing the work that British pluck and genius have been the first to venture upon. The Americans are on the track, and our Continental neighbours will not be far behind. We are glad that the extended circumnavigation expedition is in process, and we believe that if nothing unforseen occurs, Prof. Wyville Thomson, with a staff of competent aids, will sail in the autumn on their long journey, which cannot fail to have the most important bearing on our future advance in such studies. Such a journey as this, however, instead of making more modest dredging operations of no avail, vastly increases their inportance; and it is not too much to hope that the time is not far distant when men of money and leisure will more generally occupy their time in such pursuits. THE SOLAR HEAT HE calculations presented by Père Secchi, in his work "Le Soleil," relative to solar temperature and solar radiation, tending to discredit the result of recent investigations on the subject, I have carefully examined the "solar intensity apparatus," the indications of which form the basis of those calculations. This unique device will be found delineated on p. 267 of the work referred to, the accompanying illustration (Fig.1) being a fac-simile of the same. It represents a longitudinal section through the centre line, thus described :-A B and C D are two concentric cylinders soldered one to the other; they form a kind of boiler, the annular space being filled with water or oil at any temperature. A thermometer, t, passes through a tube, across the annular space, to the axis of the cylinder; it receives the solar rays introduced through a diaphragm, mn, the opening, o, of which is very little larger than the bulb of the thermometer. A thick glass, V, closes the back part of the instrument, and admits of ascertaining whether the thermometer is placed in a direct line with the pencil of rays. The interior cylinder and the thermometer t are coated with lamp black. A second thermometer, t, shows the temperature of the annular space, and consequently that of the inclosure. The whole apparatus is mounted on a support having a parallactic movement, to facilitate following the diurnal notion of the sun. The apparatus being exposed to the sun, it will be found, on observing the two thermometers, that their difference of temperature increases gradually, and that in a short time it ends by being constant. Before pointing out the peculiarities of the contrivance thus described by Père Secchi, it will be instructive to examine his "solar intensity apparatus," manufactured by Casella, represented in Fig. 2. The manufacturer publishes the following statement regarding this instrument : "Two thermometers are here kept immersed in a fluid at any temperature, and a third surrounded by the same conditions, but not immersed, is exposed to the rays of the sun. The increase of temperature thus obtained is found to be the same, irrespective of the temperature of the fluid which surrounds it." No one acquainted with the principles which govern the transmission of heat within circulating fluids can fail to observe that the thermometers applied above the central tube will not furnish a reliable indication of the temperature of the fluid below the same, nor of any portion of the contents of the annular space towards the bottom. Apart from this defect, it will be perceived that an upward current of atmospheric air will sweep the underside of the external cylinder, causing a reduction of temperature of the fluid confined in the lower half of the annular space. Again, the heat radiated by the bulb of the thermometer exposed to the sun will elevate the temperature of the air within the central tube, and consequently produce an internal circulation tending to heat the upper part of the fluid contained in the annular space. The effect of the irregular heating and cooling thus adverted to will be considered after an examination of the result of some observations recorded in Table A conducted at different times during the month of September 1871. In order to insure an accurate position, the instrument during these observations was mounted in a revolving observatory upon a table turning on declination axes provided with appropriate mechanism and declination circle. An actinometer being attached to the same table, the true intensity of the radiant heat, as well as the sun's zenith distance, were recorded simultaneously with the indications of the Secchi instrument furnished by Casella. Let us first consider the tabulated observations of September 2 recorded at equal intervals of three minutes. The indication of the two thermometers immersed in the fluid contained in the annular space first claims our attention, since the temperature of this fluid is = the principal element in Père Secchi's computations of solar temperature. It will be seen on referring to the second and third columns of the table that, while the upper thermometer indicates a mean temperature of 869, the lower one shows only 79'5°, difference 74°. This great discrepancy of temperature at different points of the upper portions of the annular space at which, owing to the inclined position of the concentric tubes, something like uniformity ought to exist, suggests a still greater discrepancy of temperature at the underside towards the lower termination of the tubes. In addition therefore to the observed irregularity of temperature at the upper part, shown by the table, no indication whatever is furnished of the temperature of the fluid in the annular space below the central tube, nor towards the termination at either side. Obviously, then, no accurate computation can be made of the degree of refrigeration to which the central thermometer is exposed by the radiation from the cold blackened surface of the internal tube, every part of which, as we have seen, possesses a different temperature compared with the rest, consequently transmitting radiant energy of different intensity. It will be found practically impossible, therefore, to determine the true differential temperature of the contents of the bulb exposed to the sun's rays and the fluid contained in the annular space. Hence, the differential temperature entered in the table, the result of comparing the indications of the thermometers, is manifestly incorrect. It will be found also by reference to the table that while the mean temperature imparted to the central thermometer by the sun's rays is 931°, the mean temperature of the fluid in the annular space is 83.3. Consequently, the intensity of solar radiation established by the instrument is only 931° 833° 9'79° Fah. Now, the sun during the recorded experiment of September 2 was exceptionally clear, the mean indication of the actinometer while the experiment lasted being 6005°, thus showing that the 9'79 energy developed was only o'16 of the true radiant 60°05 intensity. The mean zenith distance, it may be mentioned, was only 33° 24′ during the experiment. Agreeable to the table of temperatures previously published, the maximum solar intensity for the stated zenith distance is 63'35°; thus we find that the sun, as stated, was exceptionally clear while the trial took place, which resulted in developing the trifling intensity of 9'79° Fah. The result of the experiments conducted September 6th, recorded in the table, it will be seen was nearly the same as that just related, the mean temperature indicated by the thermometer exposed to the sun being 98.2°, while the mean of the two thermometers immersed in the fluid was 87.8°, hence the differential temperature 98.2987.8°10'4. The mean temperature of solar radiation during the experiment, ascertained by the actinometer, was 59.75°, the zenith distance being 35° 33'. Consequently, the intensity indicated September 6th was only 10'45 o'17 of the true energy of the sun's radiant heat, against o'16 during the previous experiment. It will be observed that the fluctuation of the differential temperature was much greater September 2nd than during the succeeding experiment, owing, no doubt, to the influence of currents of air produced by a strong breeze on the first occasion, the revolving observatory being partially open on the side presented to the sun during observations. 59'75 = = With reference to the small differential temperature indicated by the Secchi instrument manufactured by Casella, it may be urged that it is not intended to show the true intensity of solar radiation on the earth's surface, but simply a means of determining solar temperature. Granted that such is the object, yet the extreme irregularity of the temperature of the fluid within the annular space shows that the instrument is unreliable, a fact = established beyond contradiction by an experiment instituted September 27, 1871. On this occasion water of a uniform temperature was circulated through the annular space. This was effected by gradually charging this space from the top, and carrying off the waste at the bottom, holes having been drilled in the external casing for that pur pose. The result of this conclusive experiment is recorded at the foot of Table A. It will be found on reference to the figures, that the mean difference of the two thermometers immersed in the fluid was only 64′9° - 64'4 0'5°, while the mean differential temperature was augmented to 79'1° — 64°45 = 14°65° against 9'79° on the 2nd of September, although the zenith distance was greater, and the solar intensity less; circumstances which ought to have diminished the indicated intensity. It is needless to enter into any further discussion of the demerits of the instrument represented in Fig. 2. We may now return to the consideration of the device delineated in Fig. 1, copied from "Le Soleil." It will be seen that the material difference of construction is that of applying only one thermometer for ascertaining the temperature of the fluid in the annular space. Possibly this single thermometer may indicate approximately the mean temperature of the upper and lower portions of the fluid above the central tube; but it furnishes no indication of the temperature below, nor at either extremity of the annular space. The inadequacy of the means adopted for ascertaining the temperature of the internal surface which radiates towards the bulb of the central thermometer having thus been pointed out, it will be well to consider whether the expedient of passing a stream of water of nearly uniform temperature through the annular space, will insure trustworthy indication. In order to determine this question, I have constructed two instruments, in strict accordance with the delineation in Fig. 1, excepting that in one of these the concentric cylinders are considerably enlarged, the annular space, however, remaining unchanged. periments with the two instruments prove that the enlargement does not materially influence the indications, provided water of a uniform temperature be circulated demonstrated that the size of the bulb of the thermometer through the annular space. But these experiments have exposed to the sun cannot be changed without influencing the differential temperature most materially. This will be seen by reference to Table B, which records the result different diameter, conducted October 17, 1871. As on of experiments with different thermometers, and tubes of previous occasions, the instruments, in order to insure accurate position, were attached to the declination table arranged within the revolving observatory. The bulbs of the thermometers employed were very nearly spherical, their diameters being respectively o'30 and 0'58 ins. The upper division of Table B which records the experiment with the small bulb exposed to the sun, establishes, it will be seen, a differential temperature of 144° for the instrument having the 11-in. central tube, and 16° for the one having the 3-in. central tube. Referring to the lower division of the same table, it will be seen that when the thermometer with the large bulb is exposed to the sun, the differential temperature reaches 225° in the instrument containing the in. central tube, and 21'1° in the one having the 3in. tube. We thus find that, by doubling the diameter of the bulb of the thermometer exposed to the sun, all other things remaining unchanged, an augmentation of the differential temperature amounting to nearly one-third takes place. This fact proves the existence of inherent defects fatal to the device delineated in Fig. 1, rendering the same wholly unreliable. Ex Agreeably to the doctrine of exchanges, the diameter of the bulb is an element of no moment, since the internal radiation towards the same-provided its temperature be uniform-depends solely on the temperature and angular distances of the radiating points of the enclosure. Infallibility of the "solar intensity apparatus" has evidently |