ure at the base of the chromosphere to be 0,180mm. (about seven inches of the mercurial barometer), he finds the pressure at the level of the nuclei of the spots to be about 184,000 atmospheres, and the pressure in the inner region before named to be not less than 4,070,000 atmospheres. Sun-spots and Magnetic Storms.-A great magnetic disturbance was recorded at Kew Observatory, January 3d, which lasted for sixteen or seventeen hours, and during its confinuance an aurora was visible. A smaller disturbance began January 8th, also accompanied by an aurora. During the early part of the month the extent of spots on the sun was larger than usual, as indicated by the photographic registration, as follows: January 1, 6 groups, 2 of them rather large. .. 6..5 2 rather large. 66 2 large. Terrestrial Temperature and Solar Spots.Mr. Cleveland Abbe, director of the Cincinnati Observatory, contributes to the American Journal of Science for November an interesting paper on the connection between sun-spots and terrestrial temperature. His conclusions are founded on an extended comparison of Wolf's tabular view of the relative frequency of solar spots during the past three centuries, with such meteorological tables as were accessible to the author. He also studied the series of observations made on the Hohenpeissenberg, extending from 1792 to 1850, with but five years omitted at intervals. Mr. Abbe finds that the comparisons indicate a decrease in the amount of heat received from the sun during the prevalence of spots-a result in harmony with the recent investigations into the nature of the solar photosphere. The mean of several years' observations, taken at the period of maximum and minimum frequency, makes this fact more strikingly apparent. Mr. Abbe adds: "It would be interesting to seek for evidence of other temperature periods than that dependent on the eleven-year-spot period. There are, indeed, plain indications of such a period of about fifty or fifty-five years' duration-probably identical with Wolf's fifty-six year period-but our series of observations is not extended enough to justify any exact conclusion. If we acknowledge the probability of a connection between planetary configurations and solar spots, then we are at once led to make a direct connection between the former and the temperature variations. Such an investigation I have begun, and the indications are that positive results will be attained, and such as will demonstrate that the solar spots are but an imperfect index to the periodic changes in the solar radiation; these periodic changes being apparently more intimately and directly connected with the tides in the cool atmosphere surrounding the solar photosphere. The results of this investigation will be made known so soon as the recent observations on the Hohenpeissenberg can be incorporated into the work." Chemical Intensity of Total Daylight.-Messrs. the British Royal Society in March the result Henry E. Roscoe and T. E. Thorpe laid before of a long series of determinations of the chemical intensity of total daylight in a cloudless sky, made by them on the flat table-land southeast of Lisbon, Portugal, with the object of ascertaining the relation between the solar altitude and the chemical intensity. The method of measurement adopted was founded upon the exact estimation of the tint which standard sensitive-paper assumes when exposed for a given time to the action of daylight. The experiments were made as follows: Relations between the Sun's Altitude and the "1. The chemical action of total daylight was observed in the ordinary manner. 2. The chemical action of the diffused daylight was then observed by throwing on to the exposed paper the shadow of a small blackened brass ball, placed at such a distance that its apparent diameter, seen from the position of the paper, was slightly larger than that of the sun's disk. 3. Observation No. 1 was repeated. 4. Observation No. 2 was repeated. "The means of observations 1 and 3 and of 2 and 4 were then taken. The sun's altitude was determined by a sextant and artificial horizon, immediately before and immediately after the observations of chemical intensity, the altitude at the time of observation being ascertained by interpolation. "It was first shown that an accidental variation in the position of the brass ball within limits of distance from the paper, varying from 140 millimetres to 230 millimetres, was without any appreciable effect on the results. One of the 134 sets of observations was made as nearly as possible every hour, and they thus naturally fall into seven groups, viz.: "(1) Six hours from noon, (2) five hours from noon, (3) four hours from noon, (4) three hours from noon, (5) two hours from noon, (6) ent seasons are compared, or as the equator is one hour from noon, (7) noon. noon. "Each of the first six of these groups contains two separate sets of observations: (1) those made before noon, (2) those made after It has already been pointed out, from experiments made at Kew, that the mean chemical intensity of total daylight for hours equidistant from noon is constant. The result of the present series of experiments proves that this conclusion holds good generally, and a table is given showing the close approximation of the numbers obtained at hours equidistant from noon. "Curves are given showing the daily march of chemical intensity at Lisbon in August, compared with that at Kew for the preceding August, and at Pará for the preceding April. The value of the mean chemical intensity at Kew is represented by the number 94.5, that at Lisbon by 110, and that at Pará by 313.3, light of the intensity 1.0 acting for 24 hours being taken as 1,000. "The following table gives the results of the observations arranged according to the sun's altitude: Curves are given showing the relation between the direct sunlight (column 3) and diffuse daylight (column 4) in terms of the altitude. The curve of direct sunlight cuts the base line at 10°, showing that the conclusion formerly arrived at by one of the authors is correct, and that at altitudes below 10° the direct sunlight is robbed of almost all its chemically active rays. The relation between the total chemical intensity and the solar altitude is shown to be represented graphically by a straight line for altitudes above 10°, the position of the experimentally-determined points lying closely on to the straight line. "A similar relation has already been shown to exist (by a far less complete series of experiments than the present) for Kew, Heidelberg, and Pará; so that, although the chemical intensity for the same altitude at different places and at different times of the year varies according to the varying transparency of the atmosphere, yet the relation at the same place between altitude and intensity is always represented by a straight line. This variation in the direction of the straight line is due to the opalescence of the atmosphere; and the authors show that, for equal altitudes, the higher intensity is always found where the mean temperature of the air is greater, as in summer, when observations at the same place at differ approached when the actions at different places are examined. The differences in the observed actions for equal altitudes, which may amount to more than 100 per cent. at different places, and to nearly as much at the same place at different times of the year, serve as exact measurements of the transparency of the atmosphere. "The authors conclude by calling attention to the close agreement between the curve of daily intensity obtained by the above-mentioned method at Lisbon, and that calculated for Naples by a totally different method." Spectrum of a Sun-spot.-April 9, 1870, Prof. C. A. Young, of Dartmouth College, investigated the spectrum of a large group of spots a little north and east of the sun's centre. He found the lithium, calcium, and titanium lines strongly marked, and the sodium lines clearly perceptible. The titanium lines were very well defined, a circumstance at which Prof. Young was surprised, as they are inconspicuous in the normal spectrum. The same remark applies to the calcium lines in the spotspectrum. Many other lines, mostly faint, were affected to nearly the same degree, but the observer had not time to identify them. There was, at the same time, an exceedingly brilliant protuberance on the southwest limb of the sun (position angle 230°), near, but not over, a large spot which was just passing off. At the base of this prominence, which was shaped like a double ostrich-plume, the C line was intensely brilliant, so that the slit could be opened to its whole width in studying the form above described, but it was not, so far as he could see, in the least distorted. On the other hand, the F line, also very brilliant, was shattered all to pieces, so that at its base it was three or four times as wide as ordinary, and several portions of it were entirely detached from the rest. Since the C line was not similarly affected, it is hardly possible to attribute this breaking up of F to cyclonic motions in the gas from which the light emanates, and it becomes very difficult to imagine a cause which can thus disturb a single line of the spectrum by itself. Prof. Young suggests that possibly this appearance may be the result of local absorptions acting upon a line greatly widened by increase of pressure or temperature. The Kew Heliograph.-Mr. J. P. Sassiot, chairman of the committee of the Kew Observatory, has made a report of the work done at that institution during the past year. The heliograph in charge of Mr. Warren De La Rue continued to be operated in a satisfactory manner. In 237 days 351 pictures of the sun were taken. A paper embodying the positions and areas of the sun-groups observed at Kew during the years 1864, 1865, and 1866, as well as fortnightly values of the spotted solar area from 1832 to 1868, has been communicated to the Royal Society by Messrs. Warren De La Rue, Stewart, and Loewy. A table exhibiting the number of sun-spots recorded at Kew during the year 1869, after the manner of Hofrath Schwabe, has been sent in to the AstronomL ical Society, and published in their monthly notices. M. Otto Struve, director of the Imperial Observatory at Pulkowa, visited England in the month of August last. He brought with him, for the Kew Observatory, some sunpictures taken at Wilna with the photoheliograph, which was made some years ago, under the direction of Mr. De La Rue, by Mr. Dallmeyer. This instrument combines several important improvements on the original Kew model, the value of which is forcibly brought out in the superior definition of the Wilna sun-pictures. As, however, the series of the ten-yearly record at Kew was commenced with the instrument as originally constructed, it was not deemed desirable to alter it in any way until the series had been completed and reduced, and the corrections for optical distortion ascertained and applied. In the event of the sun-work being continued after 1872, it will be desirable to do so with a new and improved heliograph. M. Struve proposed to exchange the complete series of pictures obtained at Wilna for that made at Kew. He also stated that it is contemplated to erect a second heliograph at the Central Observatory at Pulkowa. A Solar Phenomenon accounted for.-In a letter read before the Royal Astronomical Society, in March, Lieutenant Herschel gave a description of some singular object which he had seen traversing the sun's disk, October 17 and 18, 1869: He was about to apply his spectroscope to the observation of a solar prominence when his attention was attracted to certain shadows traversing the disk of the sun, which became bright streaks when they had passed beyond it. At first he thought these appearances were due to sparks in the tube of the telescope, but the phenomenon lasted too long for this explanation to be available. He next thought that perhaps a system of meteors might be in transit, and prepared to subject the phenomenon to careful scrutiny. The equatorial was set in motion, the sun's disk being projected on a screen. The shadows were seen persistently traversing the solar disk, but at different velocities, the larger ones travelling most swiftly. There appeared to be two streams. He noticed that when the sun was in focus the objects were indistinct, and that they appeared very distinctly when he focussed on a distant cloud. At length, while he was attentively scrutinizing the phenomenon, he saw one of the objects come suddenly to a stand-still and then whisk off in a different direction; and then he perceived that the phenomenon he had been exardining with such anxious care was not in reality an astronomical phenomenon at all, but consisted merely of a flight of locusts. He considered, however, that not only was the existence of so enormous a swarm of locusts as the duration of the stream indicated an interesting fact in itself, but that we might find in the occurrence the explanation of many statements which had been made respecting meteors supposed to have transited the sun, and also of some peculiarities noticed by astronomers in America during the total eclipse of last year. Mr. Stone said that it was important when appearances of this sort were noticed that the observer should examine, as Lieutenant Herschel had done, whether the objects seen in transit required the same focus as the sun. This was the best way of determining whether the objects were terrestrial or not. Photograph of a Solar Prominence.-Prof. C. A. Young, of Dartmouth College, thus records a successful attempt to procure a photograph of a solar prominence, at any time and without waiting for the favorable opportunity of a total eclipse. He writes to the American Journal of Science, under date of September 28, 1870: "I have just succeeded, with the help of our skilful artist, Mr. H. O. Bly, in obtaining a photograph of one of the solar prominences, a copy of which I enclose. It was taken through the hydrogen line, near G, by opening the slit of the spectroscope and attaching a small camera to its eye-piece. As a picture of course it amounts to very little. It required an exposure of three minutes and a half, and, the polar axis of the telescope being imperfectly adjusted, the clock-work failed to follow perfectly, so that no detail is visible, and the picture will not bear much magnifying. I am convinced, however, that by using a more sensitive collodion, and taking proper pains with the adjustment of the instrument, satisfactory photographs of these curious objects may be obtained. "I may add that the spectroscope employed has the dispersive power of 13 prisms of flint, each with an angle of 55°.” The slit Solar Prominences easily seen. -Mr. Ernest Carpmael, of Streatham Hill, England, has succeeded in obtaining good views of the solar prominences by the following simple instrumental agency: He fixed one of Mr. Browning's direct-vision spectroscopes (having seven prisms) on a board which also carried a twoinch object-glass belonging to a good field telescope, and mounted the instrument, thus arranged, on the back of an ordinary bedroom mirror, and directed it at the sun. was set so as nicely to divide the D line, and a blue glass was generally interposed in front of the slit to sift the light. As the image of the sun traversed the slit at intervals, the flames appeared as bright prolongations of the F line extending beyond the sun's limb. It was also clearly seen at times that these prolongations were narrower than the F line, and were not in the centre of it, also that they were frequently detached from the sun's limb, and sometimes they were not straight: appearances depending, as is generally supposed, on the velocity and pressure of the gas in the flame. The flames were also readily seen in the C line. In observing the solar spectrum he has found colored glasses in front of the slit very useful to shut out as much as possible of the light from the parts of the spectrum not under observation. By using the spectroscope without its slit and collimating lens, and directing it toward the great nebula in Orion, it shows close together three bright images of the nebula exhibited on a continuous spectrum. Pinkish Color of the Sun.-Nature received several communications during the year from correspondents, describing a pinkish color of the sun, which they had noticed. Mr. A. S. Herschel, who was favored with a sight of the phenomenon, at Cranbrook, England, May 23d, says: The sun presented a round disk of a very unusual pinkish color, here and at Cranbrook (about five miles northeast from Hawkhurst), in Kent, between five and six o'clock P. M. on the afternoon of Monday, the 23d ult. It was so seen by myself at Cranbrook, in company with several others, who thought that the color was quite unusual, shining through a thick haze of apparently low cirrostratus, but which was perhaps rain-cloud, as the air at the time was light from the north, and cold, while the mist, or haze, seemed to be at no very great elevation above the ground, and considerably lower than those ordinary forms of cirrostratus in which halos and mock-suns are generally seen. The color observed here was a pinkish buff, or such a mixture of pink and yellow as to suggest the abundance of more blue and violet, and the absence of more yellow light than in the orange and reddish tints, generally seen in the setting sun, so as to resemble the color of very pale blotting-paper, or a light flesh-color. While the disk was still clearly seen of this color, two or three sun-spots were visible upon it with the naked eye. These could no longer be distinguished at six o'clock, when the peculiar pinkish hue was was also succeeded by the ordinary yellow of the sun's disk near the horizon, seen through a thick haze. On the same afternoon (of the 23d) the appearance of the sun's round disk through a thick cloud of haze in the sky was noticed, for a considerable time, as visible with rare and unusual distinctness at Tunbridge Wells, in Kent. Another correspondent speaks of a similar appearance of the sun observed at Rohrback, on the Moselle, May 23d. The day had been warm, without wind. Soon after 2 P. M. the horizon became charged with mist, and rain threatened. About 3 o'clock, the sun lost its brilliancy, assumed a pale-yellow hue, and might have been taken for the moon but for its diameter. A mist then began to rise, and a north wind to blow, and at 4 o'clock the sun became rose-colored, and soon after scarlet. In this case, as in that described by Mr. Herschel, the hazy state of the atmosphere was supposed to be one cause of the phe nomenon. Utilizing the Sun's Heat for Motive Power. A Solar Engine.-Captain John Ericsson, the distinguished inventor of the caloric-engine, contributed during the year a series of remarkable original papers to the London Engineering Journal, descriptive of his long and thorough investigations into the dynamic value of the sun's heat for mechanical work, and of his method of utilizing it by means of a solar engine. He omits to give plans and a detailed account of the mechanism by which the sun's radiant heat is concentrated, in order to "prevent enterprising persons from procuring patents for modifications," experience having taught him the danger of early publications of that kind. He declares, however, that he does not intend to take out a patent for his invention, and purposes to devote the remainder of his life to its perfection, and says that within a few years the entire engineering community of both hemispheres will be invited to take the matter in hand. The following are the more important parts of his statement of results and of expectations: The several experiments that have been made show that the mechanism adopted for concentrating the sun's radiant heat abstracts, on an average, during nine hours a day, for all latitudes between the equator and 45 degrees, fully 3.5 units of heat per minute for each square foot of area presented perpendicularly to the sun's rays. A unit of heat being equivalent to 772 foot-pounds, it will be perceived that, theoretically, a dynamic energy of 2,702 foot-pounds is transmitted by the radiant heat, per minute, for each square foot; hence 270,200 foot-pounds for an area of ten feet square. If we divide this sum by the adopted standard of 33,000, we ascertain that one hundred square feet of surface exposed to the solar rays develop continuously 8.2 horse-power during nine hours a day, within the limits of latitude before mentioned. But engineers are well aware that the whole dynamic energy of heat cannot be utilized in practice by any engine or mechanical combination whatever, nor at all approached; hence I have assumed, in order not to overrate the capability of the new system, that a solar engine of one-horse power demands the concentration of solar heat from an area of ten feet square. On this basis I will now proceed to show that those regions of the earth which suffer from an excess of solar heat will ultimately derive benefits resulting from an unlimited command of motive power which will, to a great extent, compensate for evils hitherto supposed not to be counterbalanced by any good. Before entering on this task of estimating the results of utilizing sun-power, it will be well to scrutinize, as closely as we can, the mechanical devices by fuel contained in that great store-house whence means of which we propose to avail ourselves of the it may be obtained free of cost and transportation. The solar engine, we have seen, is composed of three distinct parts: the engine, the steam generator, and sity of the sun's rays is augmented to such a degree the mechanism by means of which the feeble intenthat the resulting temperature will exceed that of the lowest pressure of steam admissible in an efficient engine. As to the motor itself, it suffices to say that it is essentially a modern steam-engine utiliz the steam generated by the concentrated solar rays. ing, to the fullest extent, the mechanical energy of Regarding the steam generator, it will only be neces sary to state that it is not exposed to the action of fire, clinkers, or soot, and therefore can only suffer have lastly to consider the efficiency of the mechanism from the slow action of ordinary oxidation. We by means of which the solar heat is concentrated and the temperature raised above that of the water in the steam generator. Regarding this mechanism-conit will be asked: Is it costly? is it heavy and bulky centration apparatus it may appropriately be termed so as to render transportation difficult? and finally the question will be put, Is it liable to derangement and expensive to keep in order? I will answer these questions in the same order in which they have been small-indeed, lightness is the most notable pecupresented. The cost is moderate. The weight is liarity of the concentration apparatus. As to bulk, this apparatus is composed of small parts readily put together. Regarding durability, the fact need only kept dry, may be exposed to the sun's rays during be pointed out that certain metals, however thin, if an indefinite length of time without appreciable deterioration; hence, unlike the furnaces of steam-boilers, which socn become unserviceable, structures protected as the concentration apparatus is, by thin from the mere action of the sun's rays. Another metallic plates, cannot be rendered unserviceable question will be asked, whether the solar engine will answer as well on a large as it does on a small scale? The following reply will effectually dispose of this pregnant query. It is not necessary, nor intended, to enlarge in future the size of the apparatus by means of which the solar intensity has been successfully concentrated, and the temperature sufficiently elevated to generate steam for the engines which have been built. The maximum size adopted has been adequate to utilize the radiant heat of a sunbeam of thirty-five square feet section. The employment of an increased number of such structures will therefore be resorted to when greater power is wanted, as we increase the number of hands when we desire to perform an additional amount of work. The motor itself, the steam cylinder and other parts, will obviously be proportioned as at present with reference to the pressure of steam employed and the work to be done. Agreeably to our introductory remarks, it is not proposed, in the first instance, to apply solar engines in places where there is not steady sunshine. The isolated districts of the earth's surface suffering from an excess of solar heat being very numerous, our space only admits of a glance at the sunburnt continents. An examination of the extent of these will show that the field for the solar engine, even with the proposed restriction, is not very contracted. There is a rainless region extending from the northwest coast of Africa to Mongolia, 9,000 miles in length, and nearly 1,000 miles wide. Besides the Northern African deserts, this region includes the southern coast of the Mediterranean east of the Gulf of Cabes, Upper Egypt, the eastern and part of the western coast of the Red Sea, part of Syria, the eastern part of the countries watered by the Euparates and Tigris, Eastern Arabia, the greater part of Persia, the extreme western part of China, Thibet, and lastly, Mongolia. In the western hemisphere, Lower California, the table-land of Mexico and Guatemala, and the west coast of South America, for a distance of more than 2,000 miles, suffer from continuous intense radiant heat. Computations of the solar energy wasted on the vast areas thus specified would present an amount of dynamic force almost beyond conception. Let us, therefore, merely estimate the mechanical force that would result from utilizing the solar heat on a strip of land, a single mile in width, along the rainless western coast of America; the southern coast of the Mediterranean before referred to; both sides of the alluvial plain of the Nile in Upper Egypt; both sides of the Euphrates and Tigris for a distance of 400 miles above the Persian Gulf; and, finally, a strip one mile wide along the rainless portions of the shores of the Red Sea, before pointed out. The aggregate length of these strips of land, selected on aacount of being accessible by water communication, far exceeds 8,000 miles. Adopting this length and a width of one mile as a basis for computation, it will be seen that the assumed narrow belt of the sunburnt continents covers 223,000 millions of square feet. Dividing this by the area necessary to produce 1-horse power, we learn that 22,309,000 solar engines, each of 100-horse power, could be kept in constant operation, nine hours a day, by utilizing only that heat which is now wasted on a very small fraction of the land extending along some of the water-fronts of the sunburnt regions of the earth. It will be said that these extravagant figures are devoid of practical significance. Due consideration, however, cannot fail to convince us that the gradual exhaustion of the coal-fields will inevitably cause great changes in regard to international relations, in favor of those countries which are in possession of continuous sun-power. Upper Egypt, for instance, will, in the course of time, derive signal advantage, and attain a high political position, on account of her perpetual sunshine and the consequent command of unlimited motive force. The time will come when Europe must stop her mills for the want of coal. Upper Egypt, then, with her never ceasing sun power, will invite the European manufacturer to remove his machinery and erect his mills on the firm ground along the sides of the alluvial plain of the Nile, where sufficient power can be obtained to enable him to run more spindles than a hundred Manchesters. (See also SUN, ECLIPSE OF.) Heat from the Moon.-At the June meeting of the Royal Society the Earl of Rosse gave an account of more satisfactory experiments than those previously reported, to determine the amount of heat radiated from the moon. The three-foot reflector at Parsonstown was employed as on former occasions. Earl Rosse first ascertained the percentage of the moon's heat which passes through glass, and found the titudes of the moon and distances from oppomean of nine observations, taken at various alsition, to be 11.88. Through the same glass, 86.8 percentage of the heat-rays of the sun were transmitted. It seems, therefore, to be clearly proved that there is no remarkable difference between the sun's and moon's heat in regard to their power of passing through glass. The experiment made during the previous season, to determine the ratio between the heating power of the moon and of the sun, was repeated with more care, and the value found, taking what appeared to be the most probable mean heating power of full moon, as determined on various nights, was: moon's total heat, 1; sun's total heat, 82,600. The observations were examined with a view to ascertain how far the heating power of the moon's rays varies with her altitude. Owing to the interference of clouds, and the limited range of altitude within which the observations were made, the results were not given in detail, but Earl Rosse says that the heating power of the lunar rays appears to diminish with her altitude only about a third as fast as the intensity of the solar chemical rays, as ascertained by Roscoe and Thorpe. An attempt was made to ascertain, by comparing two measurements of the moon's light at different altitudes with two corresponding measurements of her heat, whether our atmosphere intercepts the heat-rays to a greater extent than the luminous rays. It was found altitude in the proportion of about 3 to 1, the that, while the light was diminished with the diminution of the heat was in the proportion of about 5 to 1. In consequence, however, of much of the moon's light and heat being intercepted by hazy clouds or condensed vapor, at the lower altitude, the experiment was inconclusive as to the effect of a transparent atmosphere on the dark rays of heat. The observations showed a general accordance between the variation of the moon's radiant heat with her phase, and the corresponding amount of her light, as deduced by calculation. The Council of the Royal Society, at the Annual Meeting in February, after stating the results of Lord Rosse's earlier observations on Lunar Radiation (see ANNUAL CYCLOPÆDIA for |