SNE 255 zs nwame grize = earsa se des ee Sap ates ees : oy Ses oe cane gen et ; 8235 a nee ass ee) SSA Ty RID 2 BOAT ates ws ma —n oo ee ort OD Oe PV IE Pes Ce ey > = = he $ < I 4 x weer A TO mm amet a a As eS 1 & SIRLOIN FAL A729, ern 14 VAS ee fs ites REP ORD OF THE BET Ht Mace iNG: OF THE AUSTRALASIAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE, ADELAIDE, SOUTH AUSTRALIA, SEPTEMBER, 1893. a> = Ce EDITED BY: RALPH TATE, F.G.S., F.L.S. ES Hs RENNIE, M-A:. .D:Sc: W. H. BRAGG, M.A. PUBLISHED) BY THE) ASSOCIATION. ~—_—S SESS SESS SES SSS PERMANENT OFFICE OF THE ASSOCIATION: DHE UNIVER SLDY, Gi BE aS YD NE Oe NESW, “e <5. a nie SouTH AUSTRALIA: _ C. E. Bristow, GOVERNMENT PRINTER, _ NoRTH-TERRACE, ADELAIDE. (1894. Tg.. (y Mt eres? “ SONTENTS. ‘é as w . @ & a PAGE Objects and Rules of the Association .. ee Se ve 30 xe Officers and Council, and Members of Committees Ms we ol XV Presidents, Vice-Presidents, and Secretaries of Sections aie qe XVI. General Programme of the Meeting a6 oe 6 XVII. Extracts from the Minutes of the geen of the General ‘Council September 26th, 1893 oe ee AP SK Extracts from the Minutes of the Mectite of the General Gonnnily October 2nd, 1893... oe ac e ve we >O.dic Committees of Investigation Appointed at the Wee of Gate Council, October 2nd, 1893 .. ar ae ole SKI.) RL Table showing Attendance and Receipts, and Sums ae on Account of Grants for Scientific Purposes 58 yh) Ve General Statement of Receipts and meanenciture for Adelaide Mocting XXV. Balance-sheet Seismological Committee .. ic aie ee -. XXVI. Donations to Library is oc ve ie fe ae ee XVLls PRESIDENTIAL ADDRESSES. Address by Proressor Ratpu Tare, F.G.S., F.L.S., President of the Association .. 1 Address by H. C. Rosen, C. M. G., B. A; F. R. S., President of Section A. ae ae 70 Address by C. N. Hake, F. C. S., F. TC Proddent of ‘Boction B. ae 97 Address by Str James Hecror, K.C.M.G., M.D., F.R.S., President of Section C. .. : : BO 103 Address by C. W. bz Vis, M. ALS, Pisaiaent of econ D. ac we 104 Address by A. C. MacDonatp, F. R.G.S., President of Section E. .. 119 Address by Rzy. 8. Exxa, President of Section 1 Dee ee 133 Address by H. C. L. AnpErson, M.A., President of Section G. ee 144 Address by R. J. Scorr, A.M.I.C.E., President of Section H. .. 166 Address by A. Mautr, President of Section J. ate 176 Address by Prorzssor Lauriz, LL.D., PORTet of Bacon ae 196 REPORTS OF COMMITTEES. Report of Committee on Seismological Phenomena in Australasia .. 207 Report of Committee on the Systematic Conduct by the various Governments of Australia of the cance Work of the different Geological Surveys . fe . - : 226 Progress Reports of the Garantie upon the aa priivcs of Glacial Action in Australasia during the Tertiary and Post-Tertiary Eras 229 Report of Committee on the Protection of Native Fauna as ne 241 2% a U . PROCEEDINGS, OF THE SECTIONS: Section A. ASTRONOMY, MATHEMATICS, AND PHYSICS. MG 13. 14. On the Construction of Pendulum Apparatus for Pah eases Obser- vations of Grayity. By E. F. J. Love, M.A. ae se .*On-some Drawings, showing the Effect of the raph of a Solenoid on‘the:Form of its;Kquipotential Surfaces. By C.. C..Farr, B.Sc. . A Review of Meteorological Work in Australia. By Sir C, Toa Ki MG. MA. FIR.S. .. on oe . . Some of the Difficulties in making Exact Observations in Astronomy. By W. E. Cooxg, M.A. Ac an : . Earthquake Intensity in Australasia. By G. nbeede M.A. be . Origin of Earthquake of January ane 1892 (Australia and Tasmania). By'G. Hocsren, M.A.. “e te ae +e . The ‘Fides of Port Adelaide. By R. W. aoe M.A., and Cart. INGits .. 3 Lf of . as . The Application of Mathematies to Actuarial Science. By J.J. Stuckey, M.A. . An Azimuth Diagram. By Capt. WEIR .. <6 ve . On Stokes’ Theorem. ‘By’G. Frevnrt, ‘Licencié-és-sciences Mathe- matiques . From Number to Quaternions. By G. Fievrt, Licencié-és-sciences Mathematiques te ve al we . On Measurements of Double Stars. By H.C. Russexz, C.M.G., Bx. ERB... oie The Thermo-electric Diagram. By W.H. Sreezz, M.A... A Peculiar Thermo-electric Effect. By W.H. Srerzz, M.A. Section B. CHEMISTRY. . Notes on Determinations of Sugar in Samples of Musts of Vietorian Wines. By W. Percy Wirxinson (Government BY THE PRESIDENT, He Cy RUSSELL BAL, © NEG. er Ras. Government Astronomer, Sydney. THE PROGRESS OF ASTRONOMICAL PHOTOGRAPHY. Our section embraces a wide range of subjects, and the honorable position in which you have placed me to-day gives me a recognised right to select a theme for my address from any of these subjects, and to treat it in one of two ways—either to endeavor to add some- thing of my own to the present sum of knowledge, or to endeavor to pass in review what has been done. My impression is that the latter is the better course, and I hope you will be able to agree with me. j I will confine my remarks to a branch of one of our subjects which, within the past twenty years, has done more than any- thing else to accelerate the progress of our knowledge and to extend our grasp of the grand truths of astronomy. I refer, of course, to the application of photography to the wants of astronomical research. Coming inat first as another possible aid to the observer, it has already shown us that in many cases the observer must stand aside while the sensitive photographic plate takes his place and works with a power of which he is not capable; and | feel sure that in a very few years the observer will be displaced altogether, while his duty will be done by a new sensitive being, not only taking in the visual ray, but also the actinic rays into ultra violet—a being not subject to fatigue, to indigestion, to east winds, to temper, and to bias, but one, above all these weaknesses, calm and unruffled, with all the world shut out, and living only to catch the fleeting rays of light and tell their story. It has been well said by a very gifted writer' that ‘‘the invention of the telescope itself does not mark an epoch more distinctly than the admission of the camera to the celestial armory. All the con- ditions of sidereal research in especial are being rapidly transformed by its co-operation.” By this new lever the progress of astronomy is being urged for- ward at a rate which accomplishes more in ten years than was PRESIDENT’S ADDRESS—SECTION A. 71 possible in a hundred years by older methods. Its whole life history covers but fifty-three years, and its infancy and youth were cramped by the want of means of existence and growth; butits latter years have been marked by a vigor which has done so much that I shall have little more than time to mark the stepping-stones in that onward march; to trace the details would take volumes. Fifty-three years ago photography was in the daguerreotype stage, when it was just possible to get a rough photograph of the moon ; forty-three years ago it had reached the collodion stage, and was capable of rendering great aid to astronomy. Its worth had been proved, and the conditions of its successful application to the wants of the astronomer were known, but the enormous value of that power was somehow overlooked. Was it that the innovation was too great to be accepted at once, or that they did not consider the matter sufficiently? If the following record of the slow progress that followed that time and the gradually accelerating progress of the last few years should enlist some other worker into the army of astronomers, it will have done something to add to our know- ledge. It is generally stated that astronomical photography began when, in 1850, Professor Bond succeeded in taking daguerreotypes of the moon with the great 15in. refractor at Harvard College Observa- tory, but there seems to be no doubt that impressions of the moon were obtained with more or less success some ten years earlier. Professor Henry Draper, of the New York University, writes? :— “The first photograph of the moon was taken by my father, Professor J. W. Draper, M.D., who published notices of them in his quarto work on the forces of organised plants, and in the Philosophical Magazine. The specimens were about lin. in diameter, and were presented to the Lyceum of Natural History of New York. They were taken with a photographic lens of 5in. in aperture, furnished with an eyepiece to increase the magnifying power, the whole mounted on a polar axis and moved by clockwork ; the time of exposure was twenty minutes.” In September, 1840, he writes :— “There is no difficulty in procuring an impression of the moon by dagueireotype beyond that which arises from her motion.” This was not his first attempt to apply photography to astronomical work, for he tried in 1884 to fix the lines of the spectrum. The sensitive surface used was bromide of silver as a coating on paper. The experiment was not a success, but it is mentioned in the Philosophical Magazine for 1843, ‘‘ and in the summer of 1842, simultaneously with M. Becqueret, by using daguerreotype plates, 1 succeeded, and in the following March sent a drawing of the photograph to the Philosophical Magazine, and in 1843 I made photographs of the diffraction spectrum by a grating both by reflection and transmission.” Arago announced to the Academie of Sciences at Paris on the 13th of August, 1839°, the great discovery of Niepce and Daguerre, 72 PRESIDENT’S ADDRESS—SECTION A. and expresses the opinion that it would be possible to make the sun and moon record their own features by photography; and, acting upon this suggestion, Daguerre tried, and failed to get any- thing more than a very faint impression, from which all detail was absent. In Arago’s Popular Astronomy there is reproduced a daguerreotype of the sun, taken, as stated on it, on April 2nd, 1845, by MM. Foucalt and Fizeau, but no particulars are given. The long exposure of twenty minutes required to get a daguerreotype of the moon no doubt deterred many who would have tried, and it was only the genius of Bond, coupled with the great refractor, which enabled him to get the first really valuable photograph of the lunar surface. It appears in Astron. Nachrichten, No. 1105, that the artists Whipple and Black (of Boston) ‘for many years before this”? had been experimenting whenever they could get the use of the great telescope, and that the earliest successful experi- ments were made with daguerreotype plates in July, 1850; but the labor and time demanded was so great that he was obliged to put the work aside until he should be able to get improved instru- mental appliances. Some of the photographs obtained were taken to England and exhibited at a meeting of the Royal Astronomical Society on May 9th, 1850, again at the meeting of the British Association in September following, and then at the Great Exhibi- tion in 1851; and they were so good that they may be said to have taken the scientific world by storm, but I find at this time no description of what they did show of the moon’s surface. The result might have been anticipated. Everybody who could com- mand a telescope from 4in. to 6ft. tried to photograph the moon with such means as he had, and in one case they induced an astronomer, Mr. De La Rue, to become a worker, and his energy and success did very much to promote the study of astronomical photography I have said that at the time no measure of what was meant by ‘** good” photographs of the moon was given, but four years later we find a measure of the term good applied to them. In the British Association Report for 1854, p. 10, the Rev. J. B. Reade, M.A., F.R.S., writes :—‘ The daguerreotype produced in the Bond refractor possesses a latent sharpness which is difficult to see, but which was brought out by taking a copy of it with a camera. ‘This copy was compared with his own photograph, and he found in both the Mare Crisium with bright surrounding country which separates it from Mare Fecunditatis, and Mare Tranquilitatis, the crater Menelaus, and the ray of light extending from it across the Mare Serenitatis, the semicircular ridge round Mare Imbrium and the unreflective crater Plato,’’* so that Bond’s picture of the moon must have possessed a large amount of detail. Mr. Dancer’, of Manchester, seems to have been the first in England to follow Bond's lead, and in February, 1852, made some sharp pictures of the moon, using a 4}in. equatorial. These are PRESIDENT’S ADDRESS—SECTION A. 13 believed to be the first taken in England, and were of such excel- lence that they would bear examination with a compound micro- scope with a 3in. objective. Professor Bond® had not been content with his successful photo- graphs of the moon. He wished to see what could be done with the stars; and, on July 17th, 1850, Mr. Whipple, under his direction, placed a daguerreotype plate in the focus of the great refractor and obtained the first known stellar photograph—a picture of Alpha Lyre. ‘The time it took is not given, but it is stated’ that no image of the pole star could be obtained, no matter how long the exposure was continued, but an elongated image of the double star Castor was obtained before the experiments were given up. At first it seems strange thata picture of the moon could be taken with comparative ease, while bright stars, which we know are capable of recording themselves in less than one-tenth of the time required for the moon, required a much longer exposure, and in some cases would not do it at all; but it is obvious that the reason of this is to be found in the imperfection of the clockwork, which, instead of keeping the star image fixed on one spot on the plate, causes it to wander about that point until the light was too diffused to pruduce the desired effect. In 1858° Dr. Luther, of Konigsberg, showed Mr. De La Rue the daguerreotype of the total eclipse of 1851, which had been taken by Dr. Busch with the Konigsberg heliometer. Considering the state of photography at that time the successful result was remarkable, when due allowance is made for the uncertainty then existing as to the brilliance of the prominences. Towards the end of 1852 Mr. De La Rue’ took some photographs with the then new collodion process on glass. He used his 13in. metallic reflector without clock- work, and naturally met with considerable difficulty, although the time of exposure, ten to thirty seconds, was very short for those days. ‘the work required two persons, and was very tiring, owing to the number of failures. Motion was at first given to the telescope by means of the tangent screw, and then better results were ob- tained by putting the sensitive plate in a slide and moving it to follow the moon’s apparent motion. This was done by hand, and the amount of motion was determined by looking at a crater through the transparent collodion film, and keeping it bisected by cross wires attached to the back of the plate. Rough as these con- trivances seem when measured by modern appliances, Mr. De La Rue succeeded in making some excellent photographs, but, owing to the ditficulties, he came to the conclusion to discontinue the work until he should get clockwork to move the reflector. These photographs were exhibited at a meeting of the Royal Astronomical Society in 1853; they were 152;in. in diameter, and were considered very good indeed. It appears” that at this time (1853) the possibility of using photography to delineate the surface of the moon became a burn- 74 PRESIDENT’S ADDRESS—SECTION A. ing question with the British Association Committee for the survey of the physical aspect of the moon, and one of the members, Mr. John Phillips, M.A., F.R.A.S., determined to try what he could. do with his own telescope, which had a 6}in. Cooke objective and 11ft. focus. Though, in part, prepared at the beginning of the year, he was not able to make an actual beginning until July, and on 15th and 18th, assisted by Mr. Bates, he obtained some photo- graphs, which were exhibited at the British Association meeting September, 1853. The committee thought that they proved beyond a doubt that the research is of a useful and practicable kind, and may be followed up by better things. The images were on collo- dion plates, and measured 1-2in. in diameter and were enlarged by an eyepiece in the telescope to 2in., and the time of exposure was. thirty seconds. In 1854 the Photographie Society of Liverpool", being anxious to show moon photographs with others of more general character to the meeting of the British Association that year, appointed a committee of the members, of whom Mr. J. Hartnup, the astronomer, was one, to make some lunar photographs for exhibition at the British Association meeting in Liverpool in September of that year.’” The telescope used had an objective 8in. diameter and 123ft. focal length. Mr. Hartnup, of course, did the work, and got some very good photographs, of which, it is reported, the photographs of the moon shown at the meeting of the British Association at Liverpool were said to have * outstripped all other attempts made elsewhere,” and in the report of the council of the Royal Astronomical Society, February 10th, 1854, it is said that ‘ tine beautitul art of photography seems likely to be of much utility in conducing to a more accurate knowledge of the physical condition of celestial bodies.” At the Royal Astronomical Society meeting, June 9th, 1854, Mr. Hartnup exhibited ten collodion pictures of the moon, 1°35in. in diameter, and ten enlarged copies, some of which were 43in. in diameter. ‘These were all taken during May, 1854. When thrown upon the screen and made 8ft. in diameter they were much admired by the astronomers present, and the president alluded to the gratifying progress of Mr. Hartnup’s labors in connection with this interesting subject. The report of the Royal Astronomical Society for 1854 goes on to say that Sir John Herschel strongly recommended", under date April 24th, 1854", the daily photographic representation of sun spots, and the Kew Committee took the matter up and moved the council of the Royal Society, who decided that the work shouid be undertaken at Kew, and placed in Mr. De La Rue’s hands the duty of carrying out the work for the council oss, the optician, made the photo-helio- graph, which had an objective 3:4in. diameter, a focus of 50in.,. and an enlarging lens, which made the sun’s image 12in, in diameter. While this was going ov an amateur, the Rev. J. B. Reade, M.A.,. PRESIDENT’S ADDRESS—SECTION A. 7). F.R.A.S., whom I have already quoted, was very busy trying to take photographs with what must have been in those days a very large instrument. The Craigh telescope, at Wandsworth, which he used, had a diameter of 2ft. and a focal length of 77ft. It is not stated whether it was a refractor, but “the true photogenic focus was difficult to find,’ and he goes on to say, “that so large an object glass worked by hand should do so much with the stars is far from discreditable.” He then speaks of reworking the surfaces of the object glass, which seems to leave no doubt that it was not a reflector, which has one surface only. With such a long focus the moon’s image should be nearly 8in. in diameter; the time of exposure for a collodion picture of the moon was thirty-five seconds. This telescope was not equatorially mounted, and the moon's apparent motion when near the meridian was counteracted by a **screw motion given to the eye end of the telescope’; the rate was guided by looking through the collodion at a crater kept on cross wires; from a negative taken on September 6th, 1854, a negative Yin. in diameter was made, which was compared with one taken by Bond at Harvard Observatory, and Mr. Reade adds, “in this photo- graph all the more important features of the moon’s surface will be discovered by those who are familiar with their telescopic appearance.”’ I have already quoted his comparison of his photo- graph with the Bond photograph. In 1857 Professor Henry Draper", after seeing Lord Rosse’s great reflector, returned to America with his mind made up to con- struct a large reflector and use it for astronomical photography. He made a metallic reflector 15}in. diameter and 12ft. focus, but soon discarded it for a silvered glass one of same size and 12ft. 6in. focus.“ He made 1,500 photographs of the moon with it, of which the best was made September 3rd, 1863, and was enlarged to 3ft., the original being 1;4in. diameter. In 1857 Bond'*, having sup- plied the driving clock of the equatorial with the spring governor which he had inyented, again turned his attention to photography, and by the aid of the more rapid collodion plates took photographs of stars of various magnitudes up to the sixth; the brighter star of Zeta Urszee Majoris recorded itself an two seconds and the companion in eight seconds. Measures were made of these, and in this early stage it was found that the probable error of a single measure of the distance between them was only + 0°12”. Star pictures were made soon afterwards by Mr. De La Rue and Mr. Rutherford, at the meeting of the Royal Astronomical Society on November 13th, 1857. Mr. Airy, the Astronomer Royal, exhibited Bond’s photographs of this double star, Zeta Ursee Majoris, and used these memorable words—*‘ This photograph marks a step of very great importance which has been made, of which either as regards the self-delineation of clusters of stars, nebule, and planets, or as regards the self-delineation of observations, it is impossible at present to estimate the value.” Mr. Bond had, in 1857, obtained 76 PRESIDENTS ADDRESS—SECTION A. photographs of the bright stars Castor and Vega, and now with more sensitive collodion he was able to take the companion of Zeta Ursee Majoris, which is fifth magnitude and emerald green in color, so would photograph in normal conditions. The time required was eight seconds. Now the Brothers Henry photograph such a star with a ldin. star camera in one-fifth of a second. Bond’s objective reduced to 13in. would take 10-7’ to photograph this star, and therefore fifty-three and a half times longer than it does now. Hartnup, in Liverpool, 1864, took 124 times longer for the moon than it does in Sydney to-day. Mr. De La Rue’s” work in 1852 has already been mentioned, and the photographs then taken without clock movement were so promising that he determined to have a proper clock. This was not finished till 1857, and he then devoted his whole energy and his observatory to the study and practice of astronomical photography, and everyone is aware of his pre-eminent success— success eclipsing all that had been done before; and even in the present day his work must still be classed as good, but not equal to the best modern efforts. At the British Association, in September, 1859, he exhibited two original negatives of the moon, which would bear considerable magnifying power—two enlargements from these 8in. in diameter, other enlargements 33in. diameter; photographs of Jupiter, showing his belts and satellites; and one ot the Moon with Saturn near the limb taken in fifteen seconds. From the same source I learn that experiments in lunar photography were made by Lord Rosse with his 6/t. reflector. Having no clock motion for the telescope, he applied to it a sliding plate holder of the kind used by De La Rue in his first experiments, but this is said not to have met all the exigencies of the case. The telescope was wanted for other purposes, and from the fact that no photographs with the great reflector were published, it is probable they were not so good as it was hoped they would be. In his best photographs of the moon” De La Rue claimed to have recorded in a picture of the moon 1;/;in. diameter details so small that any subsequent change over a space measuring two miles each way must be detected, and claimed” to be able, with best weather and chemicals, to get a photograph of dark parts of crescent moon in from twenty to thirty seconds which would show all the parts visible near the dark limb. Having made a new driving clock in 1857, Bond devoted the great refractor at Harvard College to a series of experiments, which lasted to 1858”, making photographs of stars with various apertures from the full 15in. down to lin., to ascertain the possibility of classifying the stars by their photographic images on the plate, which, being suitable for accurate measurement, he ~ PRESIDENT’S ADDRESS—SECTION A. Fir deemed more satisfactory than the method of eye estimates in common use; and he came to the conclusion that the photographic magnitudes of stars increase by equal areas for equal increases in time of exposure, so proving that the photographic method of determining star magnitudes proceeded on the same principle as eye estimates, and anticipating by twenty-six years the same work which has been BODE TONED by several astronomers for the star charting now in progress.” Professor Pritchard, however, came to anvther. conclusion, viz., that the area of the star image varies as the square root of the time of exposure. The photo-heliograph*, which had been set up at Kew on the earnest recommendation of Sir John Herschel, already referred to, was completed at the end of February, and work on the sun was begun with it on March Ist, 1858, but at first was not continuous owing to the necessity for modifications in order to make the exposure short enovgh. This was ultimately accomplished by a shutter with a slit in it w orking ia the focus of the objective. About 1860 Mr. De La Rue” turned his attention to the possi- bility of photographing the details of sun spots with his reflector, and exhibited some on a scale of 3ft. to the sun’s diameter. The were not so good as he hoped to make them, but the cause he thought was in the secondary magnifier. They were taken in one- twentieth of a second. It does not appear that they ever came to perfection ; indeed it is well known now that the chief difficulty is vibration in the atmosphere, which is seldom absent; but he pursued the subject, and we are told in 1863” that he had exhibited some photographs of sun spots on the enormous scale of 13ft. for the sun’s diameter, and also some prints from them produced by Herr Pretsche’s process (untouched by the graver). Meantime this enthusiast, whose ability and energy for many years led the way in the application of photography to astronomy, was busy photographing star clusters with his reflector, but he found it better to use a large portrait lens, which gave very encouraging results. He remarks “ the difficulty does not consist in fixing the images of the stars, but in finding the images when they are imprinted, for they are no bigger than the specks common to the best collodion.” At this time” some curiosity existed as to the possibility of photographing comets. ‘I tried” writes De La Rue, “ with my re- flector, on the appearance of Donati’s comet in 1858, several times, without success, and on the appearance of the comet of the present year (1861) I tried not only with my telescope, but also with a portrait lens, and with an exposure of fifteen minutes, not seconds, but I failed to get the slighest trace with either.’ The care in stating the time of exposure was probably due to a report that Mr. bahern ood”, of Walton Common, in Surrey, had secured a photograph of Donati’s comet on September 26th, 1858. He used an ordinary portrait lens without equatorial stand, but set 78 PRESIDENT’S ADDRESS—SECTION A. the camera in the ordinary way, and exposed for seven seconds. The picture was about an inch long, and bore enlargement to same extent. Mr. Usherwood used a portrait lens of very short focus on a hill 700ft. high. Still the great difference between his exposure and those of Mr. De La Rue is not easily accounted for, although many accepted Mr. Usherwood’s picture as the first one ever made of a comet. We are told” that in his photographs of the moon and other objects Mr. De La Rue used a negative collodion containing iodide of cadmium and avoided acetic acid and alcohol in the bath, which he made as neutral as possible. In this way he obtained photographs of full moon, either instantaneously or in five or six seconds, and in its half phase in twenty to thirty seconds.” Early* in 1859 Mr. De La Rue had the courage to propose, and the ability finally to carry out, the transfer of the Kew photo-heliograph to Spain in 1860, in order to photograph the total eclipse of July 18th in that year. It was a bold experiment, and was crowned with success. In esti- mating the conditions we must remember that he had no chance of finding out beforehand the time of exposure for red prominences. Two photographs of the totality were secured; each had an exposure of one minute, and each showed the red prominences clearly, and served for ever to set at rest the much vexed question of those days, viz., whether they belonged to the sun or the moon, for the photographs proved definitely that the red prominences belonged to the sun. Mr. De La Rue’s station was at Rivabellosa, in Spain, and on the Mediterranean coast of Spain, 240 miles from Rivabellosa, Father Secche” had set up his observatory. and took photographs with a Qin. refractor on a smaller scale than those taken by Mr. De La Rue, but they fully confirmed the results obtained by the English party—that the prominences belonged to the sun. In the first photograph taken at Rivabellosa there was to be seen to the east of the sun a totally detached prominence or cloud of curved or boomerang form, and in the second this was partly covered by the advancing limb of the moon, and a fresh lot showed themselves on the other side. The light of the red prominences was estimated to be photographically 180 times brighter than that of the moon.* On 27th of February, 1863", and on 38rd March of the same year, Dr. Huggins led the way in photographing star spectra, and found that when the spectrum of Sirius was caused to fall upon a sensitive collodium surface an intense photographic spectrum of the more refrangible part was obtained; but, “from want of accurate adjustment of the focus, or from the motion of the star not being exactly compensated by the clock movement, or from atmospheric tremors, the spectrum, though tolerably well defined at the edges, presented no indication of lines.” Rutherford® began his work in lunar photography in 1858 with an equatorial 11}in. aperture and 14ft. focal length. Finding PRESIDENT’S ADDRESS—SECTION A. 79 it impossible to get with this instrument, intended for vision, such perfect photographs as he desired, he tried first a reflector of 13in., but ultimately gave it up, and determined to make an 114din. objective corrected for photographic purposes. This was not accomplished until December, i864, and he did not get a satisfactory negative until March 6th, 1865. The construction of this lens was difficult, because its progress could not be tested by the visual image. Mr. Rutherford got over the difficulty by testing it with a spectroscope. With this instrument stars down to ninth magnitude were taken with three minutes’ exposure, and the only photograph of the moon taken with it was sharper than any other Mr. Rutherford had ever seen. It was suggested at the time that photographs of the sky 2° ona side might be taken with it.” The power to obtain photographs of stars down to the ninth magnitude with such a small aperture and an exposure of three minutes promises to develop and increase the application of photo- graphy to the mapping of the heavens, and in some measure to realise the hopes that have so long been deferred and disappointed. On January 11th, 1869, M. Janssen®’ presented to the Academie of Sciences a short note pointing out that it was possible to isolate any part of a spectrum by placing a second slit near the eyepiece —an idea which underlies some of the most remarkable results of the present day, but it lay dormant until 1892. In 1871 Dr. Diaper* completed a 28in. silvered-glass reflector, made for the purpose of photographing star spectra, and in May, 1872, and again in August, he photographed the spectrum of Vega, showing four strong lines. Dr. Huggins, as we have seen, photographed the spectrum of Sirius on a collodion plate in 1863. In 1870” Professor C. A. Young succeeded in photographing the prominences of the sun. Negatives were made showing the solar disc on a scale 2in. in diameter, which represented clearly the general form of the prominences, but the telescope was too small for good definition, and the work was given up. ‘The light of the hydrogen line Y was used because more actinic than K. They were taken with an open slit on the spectroscope. In 1872 Mr. Ellery photographed the moon with the great reflector at Melbourne with marked success, and produced the finest photographs that had been seen up to that time. In 1873-4 many persons urged that photography should be applied to the transit of Venus, and Sir G. B. Airy, after some hesitation, adopted this as an auxiliary method, and in 1874 it was used by the majority of parties sent out as a means of determining the position of Venus on the sun. It did not prove so successful as it was hoped it would, but on many of the photographs taken in New South Wales the ring of light surrounding the planet at and near the sun’s limb was clearly recorded and shown to be brighter than the sun itself by the greater deposit of silver which 80 PRESIDENT’S ADDRESS—SECTION A. it produced. in 1874 Dr. Huggins tried to photograph the spectra of planetary nebule, but without success, the instrument at his command not being large enough. The year 1876 was an important epoch in the application of photography to the astronomer’s needs, for in that year gelatine dry plates, which had been first put on the market in i871, attained such perfection that Dr. Huggins, after an extensive series of tests comparing them with the best collodion films, gave the preference to the new-fashioned dry plates, and therefore ex- posures could be continued for hours, and even days, instead of a few minutes, the possible limit for collodion plates. Dr. Huggins used the new plates to record the spectrum of Vega on December 21st that year ; it contained seven strong lines, all of them strongly shaded at the sides, and two of them coinciding with the well- known lines of hydrogen. ‘Thus another advance was made; the greatest number of lines previously photographed was four. Dr. H. Draper* in 1877 announced his discovery of oxygen in the sun in a paper read before the. American Philosophical Society. On July 20th he found, by photographing the spectrum, a number of bright lines in the solar spectrum coinciding with lines of oxygen, and said ‘*We can no longer regard the solar spectrum as a continuous spectrum with certain rays absorbed by a layer of ignited metallic vapors, but as having also bright lines and bands superposed on the background of the spectrum.” In 1877 came another important advance. M. Janssen suc- ceeded*' in photographing the sun, with extraordinary results. The images were 12in. in diameter, and displayed remarkably sharp details of the sun spots, willow leaves, rice grains, and facule. But the most remarkable result obtained—and which was exclusively due to the improved photographic method—the whole photosphere was covered with a fine granulation of very varied forms, dimensions, and arrangements; but the most re- markable of all was the discovery of a fine photospheric network —‘‘ Reseau photosperique.’ The forms generally have rounded contours, but some are rectilinear and others polygonal; and in the intervals of this network the rice grains are distributed and definitely bounded, and in their interior /7.e , the net spaces) the ‘** granules are half obliterated, drawn out, and confused.” This great step in advance was obtained chiefty by improving the old flashing shutter and reducing the time of exposure to 3y3th part of a second. In 1878" Dr. H. Draper succeeded in getting very perfect photographs of the solar eclipse in July of that year, showing that the spectrum of the corona was similar to that of the sun—in other words, the corona must be sunlight reflected from matter in the neighborhood of the sun, and, if that accounts for the whole of its light, then it would not be possible to photograph it apart from the sun. The photograph was confirmed by the visual observations of Professors Barker and Morton, two of Dr. Draper’s party. PRESIDENT’S ADDRESS—SECTION A. 81 In a paper read before the Royal Society on December 18th, 1879, Dr. Huggins gives details of his work in photographing star spectra since he began his new and successful process in 1876, when he obtained seven lines in the photograph of the spectrum of Vega. He used a prism of Iceland spar and lenses of quartz. With this arrangement definition was so good that he could count seven lines between H and K in the solar spectrum, and could photograph star spectra from G to O in the ultra violet. He made it a practice to set the slit always to the same width (34, of an inch), and he used gelatine dry plates because they were more sensitive and could be exposed as long as he desired.” He had photographed the spectra of Sirius, Vega, Arcturus, Beta Pegasi, Betelgeux, Capella, Alpha Her- cules, Rigel, and Alpha Pegasi; also Jupiter, Venus, Mars, and por- tions of the moon. ‘The planetary spectra show no sensible modifi- cation in the violet and ultra violet parts such as would result from atmosphere on any of them. Six of the stars belonged to the ‘‘ white” class. In this paper Dr. Huggins states that the spectroscope aided by photography might be made to afford valuable information in the study of variable stars—a prophecy which we shall find was fulfilled a few years later—and that it was evident the period of the sun’s rotat‘on could be determined by spectroscopic observa- tions on each side of it. These brilliant results had not been attained without a determined battle with the difficulties in instru- ments and appliances then in use, and an amount of energy had to be expended in that way that would have borne grand fruit had instrument makers been equal to the demand of science. An indication of what had to be gone through is found in the fact that, in order to get the equatorial to follow the stars, it had been necessary to get made no less* than seven different driving clocks. In July, 1881, Professor Vogel* announced his important work and complete success in photographing the spectra of rarefied hydrogen, which gave a spectrum almost exactly coinciding with Dr. Huggins’s ultra violet spectra of white stars. Dr. H. Draper*, on March 11th, 1881, photographed the nebula in Orion, and one of the stars shown in it is of 14°7 magnitude, which is about the limit of what can be seen with a telescope of that size. So he had just brought the star camera to record as much as could be seen, and he would doubtless, had he lived a few years more, have done what has since been done, viz., photograph stars far beyond the range of vision: it was done soon after his death by A. A. Comman and others. Between 1868 and 1881 improvement in spectra photographing apparatus had been very great, but there had in the interval been no comet bright enough to try the experiment of photographing its spectrum, and Dr. Huggins” eagerly seized the opportunity on the 24th June, and succeeded in getting a fine photograph of the spectrum of bright comet 6 of 1881. The photograph was the result of an exposure of one hour, and on another bright night he F 82 PRESIDENT’S ADDRESS—SECTION A. got one with one and a half hour’s exposure. ‘Two superposed spectra are shown—one a continuous spectrum of reflected sun- light extending from F to a little beyond H: the other two sets of bright lines from the comet’s own light, with a suspicion of the presence of a third set of lines. ~ Dr. Henry Draper** succeeded in photographing the comet 6 in Aurigze on June 24th, 1881, in one exposure of two hours forty- two minutes ; the comet is shown with tail about 10° long, and several stars showing through it. He tried to get its spectrum first, with a direct vision spectroscope and an exposure of eighty- three minutes, which gave a spectrum of nucleus coma and tail, then used a two-prism spectroscope, with three exposures, 180, 196, and 228 minutes. There is in the spectrum a heavy band above H, which is divisible into lines between G and fh, and another between / and H. M. Janssen® also secured a photograph of comet 6 on July 1881. He used a telescope half a metre in zperture and 1°60m. in feeal length. The photograph was exposed for thirty minutes, and shows a tail 23° long, in which were some rectilinear rays, which were revealed by the camera, but not visible. It will be remembered that, seven days before, Dr. H. Draper, using a larger telescope and more than five times the exposure, found the tail on his photograph 10° long. On the 7th March, 1882, Dr. Huggins” succeeded in taking a photograph of the spectrum of the great nebule in Orion. He used the 18in. reflector metallic speculum, and the exposure was limited by clouds to forty-five minutes. The photograph shows a spectrum extending from a little below F to beyond M in the ultra violet; there are five bright lines as well as a narrower con- tinuous spectrum, which Dr. Huggins thought was due to stellar light. It may be mentioned that only four bright lines had been seen by the eye. Dr. Draper”, of New York, had been for eighteen months taking photographs of the nebula in Orion—to see, first, if it was changing, and, second, for the spectra of the various parts. In March, 1482, he made two good photographs with two hours’ ex- posure. On these he saw four of Dr. Huggins’ lines, but not the fifth (13730). In one of the plates is the spectrum of a tenth- magnitude star—the smallest star that had so far had its spectrum ‘photographed. On May 31st, 1882, Dr. Huggins” obtained a photograph of the spectrum of comet (Wells). It showed an essential difference between the spectrum of this comet and others. The nucleus shows a distinct spectrum, in which five brighter parts are seen, probably due to bright lines. The spectrum extends from F toa little beyond H, and no Fraunhofer lines can be seen in it. Professor Schuster’s photographs of ‘the eclipse of May 17th, 1882, show the coronal light is very strong from about G to H; PRESIDENT’S. ADDRESS—SECTION A. 83 and Dr. Huggins” thought that it would be possible, by using absorbing media, to keep out the other rays, and that it would be possible to photograph the corona by the part between G and H. The importance of this will be seen when it is remembered that the eclipsed sun is only visible about eight days in a century, and then only from small and inconvenient areas of the earth’s surface, and even this small chance is again limited by cloud and possibly in- accessible positions on the earth’s surface. The possibility of making an artificial eclipse such that the sun’s surroundings could be photographed at any time was a problem worth working at, and Dr. Huggins”, with characteristic energy, threw himself into it, and succeeded by using absorbing media in getting faint but un- mistakable photographs of the corona; the available media were insufficient for better results. In 1866 and 1868” he had tried by the same method to see the prominences, but met with only partial success for want of more suitable media. He had, however, in 1867”, by means of absorb- ing media, insulated the spectra of different parts of the sun’s surface, such as the spots and the wmnbre of spots. The photo- graphs of the corona taken by Dr. Huggins about the time of the eclipse of May 17th, 1868, were examined by Captain Abney, who said that * not only were the general features in them the same as in those taken by himself in the actual eclipse in Egypt, but also that details, such as rifts and streamers, have the same form and position,’’ but the absorbing media were not satisfactory, and he subsequently used a reflecting telescope and chloride” of silver as a sensitive surface, which is sensitive only to violet rays. With this some success was attained, but not enough to satisfy Dr. Huggins, and the work was given up, although he felt ‘that problems of the highest interest in the physics of the sun are doubtless connected with the varying forms of coronal light, which only seem to admit of solution on the condition of its being possible to study the corona continuously.” From fifty photographs of the corona which Dr. Huggins had taken in this way during May, Mr. Wesley was able to prepare a number of drawings of the corona. In 1883 Professor Pickering™® designed a star camera with the object of making regular comparisons of star magnitudes. It was so arranged that the whole heavens from 30° south to 60° north and over three hours of right ascension could be photo- graphed on one plate measuring 6in. x 8in., which was divided into six parts or pictures, all of which could be taken in eighteen minutes. The great facility such an arrangement affords for com- paring star magnitudes is obvious, and the result has fully justified the time given to it. For some years before his death (in 1882) Dr. H. Draper had devoted himself to the study of stellar spectra, and his death for a time put an end to this important work, but it was subsequently 84 PRESIDENT’S ADDRESS—SECTION A. (1883) taken up by Professor Pickering at Harvard College, and Mrs. Draper was induced to provide the money for this work as a memorial to her husband—one of the noblest monuments ever raised over a scientific man. In May, 1884, MM. Henry Brothers were making photographic experiments to test the accuracy of their method of measuring double stars from photographs, and in September the same year they had succeeded in photographing the small stars of the ecliptic. The difficulty of recording the positions of these stars in the old laborious way had induced them to try to photograph this part of the heavens in order to avoid the labor of recording them by the eye and hand. The method when completed not only recorded the stars which were required in the search for small planets, but actually made it unnecessary to look tor the planets through a telescope, because they show themselves amongst the stars by making a trail instead of a round spot, and this was done with the experimental 63in. star camera. ‘This success was so satisfactory that they began at once to make an objective of 13iin. for this special purpose, and expected to be able to photo- graph stars to the twelfth magnitude. With this larger star camera, on November 16th. 1885, they found in taking “photographs of the Pleiades a hitherto unknown nebula about the star Mia. ‘The star camera had literally called it from darkness to light. In October, 1884, MM. Henry” had got the new 13in. star camera fairly at work. They had taken a photograph of the cluster of stars in Hercules, giving it fifty minutes’ exposure, and found 550 stars of from seventh to twelfth magnitude. In another place with sixty minutes’ exposure on a surface five degrees square they counted 2,790 stars between seh and fourteenth pees an traces of Admiral iia haya in ee to this work, said they eae gone so far as to secure images of a few stars of seventeenth magnitude, ‘“‘and such stars, without doubt, have never been seen before’’—they are beyond the reach of any telescope. Their experiments proved that they could photograph a star of the first magnitude in 335th part of a second, one of fifth in one- fifth of a Recon one of sixth in half a second, one of tenth in fifty seconds, and stars of sixteenth magnitude, only just visible in the largest telescopes, in eighty-three minutes, and their experiments. led them to estimate the whole number of stars visible im Sir John Herschel’s telescope which they cculd photograph as twenty-two and a half millions. Herschel, as the result of many counts in various parts of the sky, had estimated the number he could have seen in the whole sky, if he spent forty-five years in doing it, as twenty and a half millions. It is obvious that a photograph taken now and_ showing accurately the positions of the stars will, if compared by super- PRESIDENT’S ADDRESS—SECTION A. 85 position with another taken on the same scale a few years hence, point out at once any change of position due to proper motion, &c. When, on December 13th, 1885, the new star (Nova Orionis) was discovered by Mr. Gore, Professor Pickering’s photographic star charts, showing all the stars, became at once available, and one taken on November 9th, 1885, affords unmistakable evidence that this star was then much fainter than it was five weeks later when he discovered it. On the 15th March, 1885", a very brilliant aurora at Christiana was photographed by Mr. Sophus Tromholt. He used Viogtlander’s euroscopic No. 1 lens and rapid dry plates. Exposure of from two to four minutes gave nothing, but one of eight and a half minutes showed the light in the sky, with buildings outlined on it. This was the first time an aurora had been photographed. On May 11th, 1885, Admiral Mouchez” at a meeting of the Academie of Sciences, at Paris, stated the first experiment made by MM. Paul and Prosper Henry with a camera, objective 6+in. diameter, had proved so successful that a new instrument had been constructed, which had a star camera with objective of 134in., and another telescope for a pointer alongside of it for watching the clock motion, and although it was not quite complete it had already yielded some remarkable results, and seemed to solve the question how to use photography in mapping the heavens, taking in stars down to the fourteenth or fifteenth magnitude... As we have already seen, it was thought just twenty years before this that Rutherford’s star camera had solved this question, and so it had; but the astronomical world was not ready for such a gigantic step forward, and therefore it had to wait until the general progress in astrono- mical photography had cleared the way for its adoption in recording star positions. It was found by Professor Pickering in 1885 that photographs of star spectra can be obtained by simply placing a large prism on the outside of the object glass of the telescope”, and he adopted this method with a star camera of short focus. and thus in an exposure of five minutes the spectra of all stars down to the sixth magnitude, and included in an area 10° square, are recorded; and arrangements have been made to photograph in this way the spectra of all stars down to the sixth magnitude, and it is found that the spectra of stars down to the tenth magnitude can in the same way be got in one hour. In 1886 Professor Harkness™ proposed to get over the difficulty caused by the heat of the sun on transit instruments by arranging it so that a sensitive plate could be put near the wires, and a momentary flash of light let in just enough to photograph the sun and show the wires. Several others had proposed to photograph the stars in transit, but nothing important has yet been done in this direction; but I 86 PRESIDENT’S ADDRESS—SECTION A. hope to show you presently that I have the design ready by which meridian transit work will be done by photography in a far more exact way than it can be done by the eye. Professor Pritchard, of Oxford®’, was the first to apply the photo- graphic method to the determination of stellar parallax. He con- ceived the idea in May, 1886, put it to the test of experiment by determining the parallax of 61 Cygni, not with the object of deter- mining the distance of a star so well known, but for the purpose of putting his novel method to a crucial test. He selected a star the parallax of which had been so well determined that there was a definite value before he began; probably the parallax of this star was better established than that of any other. His great success is well known, and the accuracy of the method so great, that a most satisfactory value of the parallax was obtained coming close to the mean of the four best values previously determined by older methods. The Oxford value is :— (il Ohyeattl Bs oooolonoGse Aayeistassters Sisisiata sO) wvcletepeyeyerecoke 0-438 OTC YENI salsa Geiciel cos erche trereisise. ctascists, Asitouenaitets 0-441 Anwaae 8; value? ssc. ten daeoere io to ae eee 0-348 Besselis, Wale) ga adios or apeteoi kere Atos oto oo soveterborae 0°564 Ball Valin: sporsvevchoisvees tele oieiey wile ite eieret Poche 0:468 Asap Ela, VALU 8 sta5- stains arin whol sie Maio isheraseratetarmee eels 0-261 MIGAN Set F Secreted shilentenihadcaienverete of dtarsts 0-410 The professor determined the parallax of thirty stars conveniently situated from Oxford of first and second magnitudes; and collecting those determined by Gill and Elkin of stars of the first magnitude, he was able to give in his *t Researches into the History of Stellar Parallax”’ a list of ninety-three bright stars, the distances of which have been recently measured. ‘This list includes the majority of the bright stars, and from this he deduced that the average parallax of first magnitude stars is 0°89” and of second magnitude 0-056’. There are considerable deviations from the mean in both classes; but the fact remains that the first magnitude stars are nearer to us than the second, and both very much nearer than the faint stars with which they were compared to determine their distances. On Gctober 24th, 1886, Dr. Isaac Roberts, who had been so successful in photographing faint objects, turned his telescope on the nebula about Mia, and found that it was much more extensive than had been supposed; many branchings seemed to form a back- ground for the whole cluster of the Pleiades. In April, 1887, a conference of fifty-four astronomers from all parts of the world met at Paris, and agreed upon a scheme in which eighteen of them undertook to carry out the work. All were to use star cameras of the same size and focal length and take two PRESIDENT’S ADDRESS—SECTION A. 87 sets of photographs—one including stars down to the fourteenth magnitude, the other set to take stars to the eleventh magnitude only. These are to be measured and catalogued for reference, and the heavens have been divided into eighteen portions as nearly equal as possible. On March 15th, 1888, Professor Vogel® announced in a paper read before the Royal Prussian Academy that he had found ia taking photographs of the spectra of stars that the vibrations of our atmosphere, which are so exceedingly troublesome to the eye, rendering it oftentimes impossible to make a measure, do not affect the definition of a photograph of the spectrum at all. Dr. Huggins, as we have seen, was the first to use the spectro- scope to determine the motion of stare in the line of sight, and Professor Vogel” was the first to apply photography to recording spectra in order to determine star motions in the line of sight. For this purpose he used the 12in. equatorial at Potsdam to carry the very fine spectrograph which he had designed. The work was begun in September, !888, and by May, 1891, all the stars in the northern heavens, fifty-one in all, bright enough for the purpose had been examined with this instrument, and their velo- cities in the line of sight accurately determined. On December 29th, 1888, Dr. Isaac Roberts succeeded in making a very fine photograph of the great nebula in Andromeda, which is a startling revelation of its extent and complex character. At a meeting of the Royal Astronomical Society, March 8th, 1889, Captain Abney”, the highest authority, replied, in answer to a question, that *‘I] have made experiments and can say distinctly there is, as far as I know, no light so feeble that an accumulation of it will not give an image upon a photographic plate.’”’ And not long since we were told, upon other authority, that a good photo- graph of a dark interior of a building has been taken and required seven whole days’ exposure. There seems then no reason why exposures should not be continued night after night, reaching fainter and fainter lights. Professor Pickering™ had a startling report to make in the fact that the work of photographing the spectra of all stars down to the sixth magnitude, between 25° south declination and the North Pole, was compieted in May, 1889, and that it contained 10,800 stars and 28,000 spectra; that in practice it was found that planetary spectra are readily distinguished from those of stars, and it had been decided to take the Bache telescope to Arequipa, and continue this survey to the South Pole, and Mrs. Draper has enlarged her original gift in order to determine the spectra of all stars down to the tenth magnitude; the original 28in. reflector made by Dr. Draper for star spectrum work is to be used. In 1888 and 1889 Dr. Huggins secured photographs of the spectra of the nebula in Orion, confirming his results obtained in 1882, only altering the wave length of one line from 38,730 to 3,724, and 88 PRESIDENT’S ADDRESS—SECTION A. revealing a number of additional lines in the ultra violet as well as in the continuous spectrum, and he considered it probable that these features indicate a physical condition at or near the beginning of the cycle of their celestial evolution. The white stars are distinguished by the number of their spectra lines in the ultra violet, which indicate a greater intensity of tem- perature and point to a comparatively recent formation from the condensation of highly heated matter; as these stars radiate their heat they change color, the red stars being the coldest we know. In 1890 the southern part of the Milky Way was photographed at Sydney with a 6in. protrait lens, special attention being given to to the parts that are dark to the eye. and the camera revealed a multitude of stars in them, especially in the Coalsack in Crux, in which the stars seemed about as numerous as in the parts about, and their distinctive grouping has such a strong family likeness to the parts of the Milky Way near them that there seems to be no reason to doubt they belong to the same system. In August, 1889, Professor Pickering’? pointed out that a star camera with double objective 24in. in diameter would be a power- fui aid to astronomical photography. and Miss C. W. Bruce, of New York, came forward and gave 50,000 dollars for the pur- pose of making this great instrument for photographing star spectra. On January 8th, 1890, Professor Pickering’! announced that one of the results of the work done under the Draper Memorial was the discovery of a new class of binary stars, whose components are far too close to be seen by any other method. It was first noticed that the conspicuous lines in the star were sometimes double, and an extended series of photographs revealed the fact that the duplication came at intervals of fifty-two days, and this is completely accounted for if one assumes the existence of two stars with similar spectra very close together and revolving round each other in a plane passing nearly through the sun; the doubling of the line is, of course, caused by the Fat that he star is at one time moving towards us and at another away from us. A similar case was discov ered by Miss A. C. Maury, who, when examining the photographed spectra of Beta Aurigze on forty- seven photographs, found that the star line doubled periodically like those in Zeta Urse Majoris, but at shorter intervals ; in fact, that one of the stars goes round the other in two days. Itisa startling discovery to find binary systems of this kind so very different from any previously known, and I think there can be no doubt that this fact would have been hidden for ages to come but for photography, because until the discovery was made there was no apparent reason for every day examination of the spectrum of a star; indeed, until then, when the lines were once carefully mea- sured they were put aside by the observer as finished and definite records of the star’s spectrum. These first results indicate that the components of Beta Aurige are separated by an angular interval of PRESIDENT’S ADDRESS—SECTION A. 89 only 0-004", a quantity so small that twenty years ago no one ever dreamt of being able to measure it. At the meeting of the Royal Prussian Academy of Science on November 28th, 1889, Professor Vogel” stated that he had photo- graphed the spectrum of Algol six times—three in the winter of 1888-9 and three times in November, 1889—and that he found before the minimum the lines in the spectrum of Algol are displaced towards the red, showing that the star is receding, and after the minimum they are displaced towards the violet, showing approach- ing motion, and these facts can only be accounted for by the theory that Algol is associated with a dark star, and that the two revolve in the plane of the line of sight round the common centre of gravity once in 68°8 hours. At minimum the dark star intercepts some of the light by being on this side of Algol, and the photographed spectrum further justified the conclusion that the diameter of the larger body was 1,074,000 miles; of the smaller one, 840,000 miles ; the distance between them, 3.269,000 miles; the speed of Algol in its orbit, 27 miles per second; and of the dark one, 56 miles per second, and that the system was ap- proaching the earth at rate of 2 miles per second. In March, 1891, it was announced that Professor Rowland® has accurately photographed the whole of the solar spectrum from D down to the extreme ultra violet, by means of concave gratings. It is the most perfect map of the solar spectrum that has ever been made. He has further proved that thirty-six terrestrial elements are certainly present in the solar spectrum, the presence of eight others is doubtful, and fifteen others (including nitrogen, as it shows itself under the electric spark) have not been found in it ; and it follows, he thinks, that if the whole earth were heated up to the tempera- ture of the sun its spectrum would resemble very closely the solar ‘spectrum. On August 7th, 1891, M. Deslandres exhibited the results he had obtained since May in photographing the bright lines of the solar prominences. ‘The negatives show good reversals of the lines H and K, and the first two lines of the ultra violet hydrogen lines. Professor Hale, of Chicago, also in the middle of April obtained the first reversals of the tines H and K by his method. The year 1891 will ever be memorable in the annals of astronomy as that in which the great work of a photographic ‘survey of the heavens, which was arranged in 1887 at the Paris conference, was actually begun.” The 24in. star camera, the splendid gift of Miss Bruce, was nearly finished in January, 1893, and it bad been decided to use it first at the Boyden Observatory, near Arequipa, under Professor Picker- ing. We now come to one of the most surprising results that has marked the application of photography to the wants of the astronomer. Several attempts had been made with more or less success to get a 90 PRESIDENT’S ADDRESS— SECTION A. method by which the sun’s surface and surroundings could be regularly studied, but Professor George Hale, guided by what. had been done by others, studied and succeeded in working out a new method, which seems to meet all, or nearly all, the require- ments. He had completed this work ready to take solar photographs. by January 22nd, 1892. He calls the instrument a spectro-helio- graph”, and by it the solar prominences, faculze and chromosphere, can be clearly photographed by monochromatic light of the wave length K. It is not necessary here to describe the instrument; it. will suffice if I mention the essential points of difference between the spectro-heliograph and an ordinary solar spectroscope. Let us. suppose, then, that we have a solar spectroscope. ‘The professor removes the fixed slit, and puts in its place one large enough to take in the whole of the sun and surroundings; this slit can, by suitable machinery, be made to move across the image of the sun. Thegrating is next so adjusted as to give only the K line of the spectrum. The ordinary eyepiece for viewing the spectrum is next remoyed. and in its place is fixed another movable slit, which is. moved by the same machine as the other one, and at a definite relative rate; all being adjusted, the light of the K line of the spectrum will pass from the grating through the second slit, the use of which is to prevent any side light near the K line from falling on the sensitive surface ; to complete the arrangement it is only necessary to put a sensitive plate very close to the second shit. Everything being ready the telescope is uncovered and the slits set in motion. As the first moves across the image of the sun the second moves across the sensitive plate, and any K light passes through it and leaves its record on the plate in a_ position relative to that on the sun. Thus, practically, a series of very fine lines, sections as it were, across the prominences are recorded side by side until the whole dise is included, and the photosphere and prominences clearly photographed. ‘The operation requires first- rate apparatus and every precaution to ensure success 1 will only mention one contrivance. Whenthe slitsareadjustedand everything ready to take the photograph, a round disc of metal is put in front of number one slit; it is nearly as large as the image of the sun, and practically makes an eclipse of the brighter parts, leaving only the edge of the sun, the photosphere, and prominences and corona to pass to the spectroscope.’ The next point is to secure on the same sensitive plate a photograph of the facule and spots. The grating is now set, so that the combined slits only allow the tacule light to pass. Allis then prepared. so that the slits will move across the sun’s disc and across the plate. ‘The disc is re- moved, and the facule spots recorded in their true relative positions to the prominences. ‘Che apparatus is quite successful, and the professor thinks that, with a modification, he can also: photograph the corona; but up to latest reports this has not been successful. PRESIDENT’S ADDRESS—SECTION A. 9I Encouraged by the success of his spectro-heliograph, Professor Hale has designed for the Yerkes Observatory, Chicago, an improved spectro-heliograph, which will, when finished, carry seventy-two sensitive plates, and automatically record on each of them at any interval that may be desired complete pictures of the spots, faculee, photosphere, and prominences in true relative position on each plate. All that will be necessary will be to set the telescope, wind up the machinery, and set it to work, the only limits being, first, that it takes two minutes to get a complete picture of the sun; and, second, the number of plates put in the wheel that carries them. Under the old system it was a good hour’s work to record the prominences alone; the new apparatus will do the same work far better in one minute. So far it has not been found impossible to photograph the corona with this apparatus, but experiments are in progress and confidently expected to succeed by which a modified spectro-heliograph will photograph the corona, using only the ultra violet light. One remarkable result of Professor Hale’s spectro-heliograph work is the abundance of facule all over the sun from pole to pole, and seen thus they are of curved forms, generally like the tigure 3, though spread over the whole surface they are strongest within 40° of the equator north and south, and the greater part of them are invisible to the eye, and in Professor’s Hale’s opinion they ‘are not to be confused with Janssen’s reseau_ photo- sperique.”’ Janssen, in 1869, in a paper read before the British Association meeting at Exeter, pointed out that it was possible to isolate any particular line in the spectrum by using two slits, one being near the eye. On March 22nd, 1892, a photograph of Swift’s comet was taken at the Sydney Observatory, which shows eight narrow rays ex- tending from the head. As these were all quite invisible with the large refractor, it is probable that they were composed of blue or violet light, because if of white light they would have veen visible through some of the larger telescopes turned to the comet, if not through the Sydney refractor. Professor Schaerberle”, at Lick Observatory, has recently photo- graphed the corona by the method of absorption introduced by Dr. Huggins, and has obtained satisfactory pictures. He con- ducted the Lick Expedition to observe the solar eclipse of April 16th, 1893, and in his report he says that the observations and photographs of the eclipse taken confirm his opinion of the structure of the corona, and his photographs of it by Dr. Huggins’ method. One of the eclipse pictures shows the dark sun 4in. in diameter, and the corona round it covers a plate 1sin. x 22in. In March and April, 1893, selected parts of the Milky Way were photographed at Sydney with the large star camera and specially sensitive plates, with the results that parts that look nebulous in 92 PRESIDENT’S ADDRESS—SECTION A. the photographs of 1890 are simply masses of stars, that a group that Herschel with his great telescope estimated to contain 200 stars, on the photograph contains 14550, and that a well-defined portion in Sagittarius, which in the 1890 plates contained eighty stars, is now found to contain 1166, or fourteen times as many. Professor Kapteyn, from his study of photographs taken at the Cape of Good Hope, was able to announce in March, 1898, that stars near the Milky Way and in it are photographically brighter than stars of the same visual magnitude which are at a distance from the Milky Way, and the difference is in proportion to the distance. The photo-spectrographic method of measuring star motions has already been referred to, but the results have recently, in tne hand of Dr. Kempf, given a new and quite independent determina- tion of the rate and direction of the sun’s motion in space. Dr. Vogel thought that fifty-one stars were not enough to give the result desired, but as the present apparatus is not powerful enough to determine the motion of any more stars the computa- tion was made, with the result that “‘ the apex of the sun’s way ” situated in R.A. 206° and north declination 46°, in the constellation Bootes, and that its motion in that direction is at the rate of eleven and a half miles per second. Many previous attempts have been made to locate the ‘\ apex of the sun’s way,’ and the placed it in about R.A. 267° and north declination 31°. This older method affords no means of determining the rate of the sun’s motion, unless an assumption was made as to the distances of certain stars, and this made the velocity sixteen miles per second, which does not differ very much from eleven and a half— the value determined from photographs. As an index of the great accuracy attained at Potsdam in determining motion in the line of sight, it may be mentioned that six photographs of the spectrum “Arcturus were taken, from which its motien in the line of sight was determined, and Professor Keeler, using the great Lick telescope on three nights, determined the same quantity by eye measurements, and the two values agree within the tenth of a mile per second. Professor Keeler, using the great Lick telescope, 86in. in aperture, has determined the motion of several nebule in the line of sight, and finds values ranging from two to twenty-seven miles per second, and in one case forty miles per second. In this brief outline of what photography has done, and is doing, much has been omitted for want of space, and in many places the bare facts are given in order of time simply to recall important steps in the progress to your memories. Even in its infancy photography was received kindly by astronomers, and although much was expected from it nobody dreamt what it would be to- day. Sir George Airy, as we have seen, was very much impressed with what one saw, and he felt that a new power in PRESIDENT’S ADDRESS—SECTION A. 93. astronomy was coming to the front; but it is evident that he had no adequate conception what it was going to do for exact records or for descriptive astronomy, or we should have had his great powers devoted to its development. But who could dream in those days that it would be possible now to say, as Professor Pritchard® has said, that in measuring distances of over 2,000 seconds of arc for his photo-parallax experiments he had found the probable error of the distance between two stars so measured to be only one-tenth of a second of arc, and that the camera and spectroscope combined, in Professor Vogel’s hands, had separated a double star with a dis- tance of only six-thousandths of a second of are—a quantity so small that our great telescope will have to be enlarged thirtyfold before we can see it. And Professor Vogel’s determination of star motions in the line of sight has, in jhe opinion of competent persons, shown that attempts to determine the motions of stars in the line of sight without the aid of photography was little better than a waste of time. And Professor Keeler*', recently in charge of the great Lick telescope, and therefore having full knowledge of the powers of the greatest telescope in the world, writes it has been shown ‘that visual observation of the spectrum cannot in general compete with photographic methods applied to the same as even much smaller telescopes.”’ Indeed no one can study the results obtained by photography where it has been fully applied without being impressed by the fact that the results are not only far in excess of the amount possible by eye observation, but also of far higher value, and that after a time photography will displace the observer from all astronomical instruments and do much better work than he could ever hope to do with his eyes. We have to-day passed in hurried review the application of photography to the wants of the astronomer in delineating the moon’s surface in the study of her libration; to recording the sun’s disc, his spots, facul, rice grains. photosphere, red prominences, the corona in actual and im artificial eclipse; to the sun’s motion in space; to the sun’s rotation periods; to recording that wonder- ful spectrum with its thousands of lines; to the record of double stars; star charting; star magnitudes; to their classification by quality of light; to recording their almost inconceivable numbers ; to star drifting; to star motions in the line of sight; to double stars so close and so remarkable that they can only be recorded by this means; to the record of all the visible stars in the sky for the purpose of detecting changes of magnitude: to the record of the spectrum of every ian doean to el tenth magnitude; to finding invisible stars and invisible lines in their spectra; in recording the forms and details of nebule; to their spectra, to show that he eye does not see all details they present nor their extraordinary exten- sion; its application to recording the form and appearances of comets ; to the record of the invisible rays in their tail; to their spectra; to the surface-marking of planets; to their spectra ; to 94 PRESIDENT’S ADDRESS—SECTION A. show their satellites, and to record the places of the satellite of Neptune, which it is difficult to see with any telescope, but is photo- graphed easily; to proving that the light round Venus in transit is much brighter than the sunlight itself; to recording the lines in the ultra violet of the spectra of heavenly bodies, lines the exis- tence of which otherwise must have remained for ever unknown to us, because they are invisible. We have taken only a passing glance at many of the applications of photography, and each of them would repay a careful study. Indeed, the results obtained by means of photography come upon us so fast that one hardly realises their importance. Think for a moment what it means to catch a fleeting ray of light that maybe has for hundreds of years been flying through space with the inconceivable velocity of 180,000 miles per second, to catch and fix it on a photographic plate, and extort from it, not only where it came from, but the physical and chemical condition of the star it came from—whether it be old or young, coming to us or going away, whether the parent star has a bright or dark companion, their dimensions, distance apart, speed in their orbits, and their mass. To extort all this from a wandering ray of light is more wonderful than anything in romance; or, to turn in another direction, the photographic survey of the heavens now in progress, and many plates of which have been taken, will contain a record of at least 3,500 stars for every 1 we can see with the eye. But grand as the work has been so far, there is yet much to do, and more fields to conquer. It must replace the transit instrument with another more accurate and capable of recording all stars to the tenth or twelfth magnitude. It must find an instrument large enough to record the closest double stars, and such clusters as Omega Centauri. It must write at short intervals the exact forms of nebule as well as their spectra, showing motion in space, and so record their changes in form as well as their disappearance and appearance that any change will be detected ; must make still more aceurate records of the magnitudes and spectra of the stars; must sound the star depths in all directions so that photographs of star clusters will show the stars still more accurately, and must find an automatic camera suited to its needs that will keep records of sun, moon, aud stars; must picture the moon as perfectly as we can see it, and make it possible to compare minute details month after month, and so detect any changes. No doubt there are difficulties in the way, and even this moderate view of the wants of the future presents many, but they are not insuperable. The army of science is in one respect like the army of war—it is stirred to conquering effort by the difficulties that stand in the way. Given a citadel to be won, and there is always a forlorn hope to win it. Given a glimpse of one of nature’s secrets—the photosphere, the prominences, and the corona hidden by the sunlight, except for a moment in each century—and at once yousee the army: Huggins, PRESIDENT’S ADDRESS—SECTION A. 95 and Airy, and Young, and Janssen, and Lockyer, and a host of others, all battling with the overpowering light of day in order to win the secret that it hides, winning bit by bit of the difficult way until success is attained. With such a record of unexpected successes in the past, and so much more that is possible now. it would te folly to attempt to forecast what another ten years will bring forth. Everything points to an enormous increase in the details of the known, and to at least an equally great advance into the unknown. Photographs taken three years ago filled the dark places of the southern Milky Way with stars, ani brought at least strong evidence that they have grouping exactly resembling the Milky Way near them—a sort of family likeness which cannot be mistaken. This year some Milky Way spaces taken with the camera of 1890 have been probed by the large star camera, and it may be mentioned, as a measure of the difference of the two instruments, that a well-defined but small space which in the 1890 photograph contains eighty stars, is found in the 1893 photograph to have fourteen times as many stars, or 1166. Now it is possible to-day to get a camera made ten times as powerful as those in use, and there is a talk, and one may say a probability, that in the very near future one will be made a hundred times more powerful. Moreover, the experience of the past has been that the limit in power of the telescope of one age is not the limit of the next. There has been a gradual expansion in the arts, which the astronomer has taken advantage of, and there is every reason to suppose this will continue in the future to an extent of which we can form no estimate. One is tempted to ask— Will the star depths unfold in the same ratio? And the reply comes in the words of the German poet—* Other worlds more biliowy, other heights and other depths are coming, are nearing, are at hand ; for end there is none to the Universe of God!” NOTES. 1. Miss Clerke: System of the Stars, p. 23. 2. Nature, vol. x., p. 243. Quarterly Journal Science, vol. 1., p. 381. 3. Nature, vol. xuiv., p. 380. 4, Nature, vol, x1r., p. 568; also Observatory, vol. 11., p. 13. 5. Chamber’s Astronomy, third edition, p. 708. 6. An Investigation into Stellar Photography, vol. x1., North American Academy of Sciences. 7. Astron. Nachrichten, No. 1105. 8. Phil. Trans., 1862, p. 333. 9. British Association Report, 1859, p. 134, e¢ seg.; also Astronomical Register, 1883, p. 65. 10. British Association Report, 1853, p. 15. 11. British Association Rep srt, 1854, p. 66; also Astronomical Register, 1563, p. 65. 12. Royal Astronomical Society Monthly Notices, vol. xv., p. 132. * 13. Royal Astronomical Society Monthly Notices, vol. xv., pp. 140 and 158. 14. This was the second time, see Cape Obseryations, p. 435, foot note. 15. British Association Report, 1854, p. 10. 16. Quarterly Journal of Science, 1864, pp. 381 and 384. 17 Quarterly Journal of Science, 1864, p. 382. PRESIDENT’S ADDRESS—SECTION A, . An Investigation into Stellar Photography by Professor Pickering; see also Astron, Nachrichten, 1105; also Astronomical Regiscer, vol. 1., p. 65, which says the moon photos. were 3in. in diameter. . British Association Report, 1859, pp. 130, 139, 140. . Royal Astronom eal Society Monthly Notices, vol. x1x., p. 354. . Royal Astronomical Society Monthly Notices, vol. x1x., p. 356. . British Association Report, 1859, pp. 139, 140; «lso Astron. Nachricten, 1105, 1129, and 1158 ; also Monthly Notices, vol. xtx., pp. 138 and 139. . Proceedings of Royal Society, 1886, No. 247, p. 207. . British Association Report, 1859. p. 149. . British Association Report, 1861, p. 96; also Royal Astronomical Society Monthly Notices. p. 278, with plate. . Astronomical Register, vol. 1., p. 118, 119. . British Association Report, 1861, p. 95; also Royal Astronomical Scciety Monthly Notices, vol. xrx., p. 138. . Royal Astronomical Society Monthly Notices, vol. x1x., p. 138. . Astronomical Register, vol. 1., pp. 67 and 118. . British Association Report, 1859, p. 137. . Phil. Trans., 1862, p. 333. . Astronomical Register, vol. 1, p. 119. . Phil. Trans., 1862, p. 405. . Phil. Trans., 1864, p. 428. . An Investigation into Stellar Photography, by E. C. Pickering, p. 181; also Astrono- mical Register, vol. 11., p. 109. A list of Rutherford’s photographs is given in the Smithsonian Miscellaneous Collections, No. 311, p. 8. . Quarterly Journal of Science, 1865, pp. 651 and 652. . Comptes Rendus, 1869; also British Association Report, 1869, p. 25. . Nature, vol, xx1., p. 23; also Astronomy and Astro-Physics, June, 1893, . Nature, vol. 111., p. 111. . Nature, vol. xvyr., p. 364. . Nature, vol. xviil., p. 643. . Nature, vol. xviir., p. 43. . Nature, vol. xxr., pp. 269 and 270. . Nature, vol. xxx1., p. 84. . Nature, vol. xxi., p. 410. Nature, vol. xxivy., p. 308; also An Investigation into Stellar Parallax, by E. C. Pickering, p. 181. British Association Report, 1881, p. 520, with plate; also Nature vol., xxiv., p. 464, . Nature, vol. xxrv., pp. 236 and 308. . Nature, vol. xxv., p. 132. . Nature, vol. xxv., p. 489. Nature, vol. xXv1i., p. 33. . Nature, vol. xxvi., p. 179. . Nature, vol. xxvit., p. 199. . Nature, vol. xxvir., p. 199. . Royal Astronomical Society Monthly Notices, xxviitr., p. 88, and xxIx., p. 4. Royal Astronomical Society Monthly Notices, vol. xxviit., p. 88. Nature, vol. xxviit., p. 606. . Nature, vol. xxviil., p. 255. . Astronomical Register, vol. xxty., pp. 246-7; also Nature, vol. xxxIv., p. 35. Nature, vol. xxxv., p. 37; also Royal Astronomical Society Notices, vol., xLv1., p. 107. . Nature, vol. xxx1., p. 480. . Nature, vol. XxxII., p. 70. . Nature, vol. xxxv., p. 37. . Nature, vol. xxxyv., p. 16. . In his Researches into Stellar Parallax. Nature, vol. xxxvir., p. 616; also Antronomy and Astro-Physics, Feb., 1893, p. 150, . Astronomy and Astro-Physics, March, 1893, p. 271. . Observatory, vol. x11., p. 165. . Nature, vol. x1.., p. 17. Nature, vol. x., p. 417 and 418. Royal Astronomical Society Monthly Notices, March, 1890, p. 296. . Nature, vol. xu1., p.. 164. . Nature, vol. xii1., p. 452. Nature, vol. xLiv., p. 438. . Nature, vol. xLvui., p. 304. Astronomy and Astro-Physics, May, 1892, p. 408. . Astronomy and Astro-Physics, May, 1892, p. 408; also Aug., 6 3. with two plates, actual photographs. Nature, vol. xivit., p. 498. Astronomy and Astro-Physics, October, 1892, p. 741. . Astronomy and Astro-Physics, March, 1893, pp. 255 ad 260; also May, 1893, p. 463. . Researches in Stellar Parailax, by Professor Pritchard. Astronomy and Astro-Physics, June, 1893, p. 351. Section B. CHEMISTRY. ADDRESS BY THE PRESIDENT, CoN: FAKES bE Coe bel. Chief Inspector of Explosives, Victoria. RECENT DEVELOPMENTS IN MODERN EXPLOSIVES. In compliance with your request to read an address before you Association at this meeting, I have chosen a subject—I am afraid rather a dry one—but it is one I am most conversant with; and, in dealing with it, I do not consider it advisable to repeat the so often mentioned generalities about the manufacture and composition of explosives, but will only touch lightly on representative types, and on improvements which have gradually led up to the reliable pro- pellants of the present time. Within the memory of many here present gunpowder was practically the only explosive available, both for industrial and military purposes, but the discovery of guncotton and nitro-glycerine has gradually encroached upon its old domains and is displacing it from its former unique position. It is, however, still the most important and most commonly used explosive, both in the industries and for warfare. Within recent times gunpowder was made ina haphazard sort of way, and one kind was used for all Service pur- poses. It was known as a violent explosive ; but no one troubled about its characteristics, or about the pressures exerted in the gun, or the muzzle velocity of the projectile. With the old smooth-bore gun, with plenty of windage, no one could predict whether the projectile would deflect to the right or to the left. But in spite of all this the obsolete gunpowder, fine grained and quick burning, was well suited to the ordnance, and very effective at close quar- ters. The composition of Service gunpowder has undergone very little change in recent times; but, although still a mechanical mixture of saltpetre, sulphur, and charcoal, the care bestowed on its manufacture makes it possible to obtain with certainty uniformity of results under similar conditions, as if it were a chemical com- bination. These results, however, have only been obtained after long study, patient research, and under difficulties which few unacquainted with the subject will appreciate. The principle G 98 PRESIDENT’S ADDRES —SECTION B. upon which improvements in modern gunpowder are based lies in the slowing down of the powder, and this alteration became neces- sary by the introduction of rifled ordnance. It is now required that when the charge is fired in the breach of the gun the com- bustion shall commence comparatively slowly, so as to overcome the vis énertie of the projectile, and that as the projectile passes up the bore of the gun the combustion shall increase in rapidity, so as to supply a progressively increasing quantity of gas to accelerate the momentum of the shot, which should leave the muzzle of the gun with the maximum velocity. The Service powder known as R.L.G. represents the first attempt in this direction, and this improvement was accomplished by increasing the size and shape of the grains. A further improvement was made by increasing the density of the powder, as in P2 powder, and it was found on experiment that a charge of P2 powder equal to that of R.L.G. gave considerably reduced pressure in the gun, accompanied by -an increased muzzle velocity of the projectile; but, as even these powders exerted too great a strain upon the gun, it became neces- sary to slow down still more, and many suggestions were made with this object in view. General Rodman, of the American Service, first overcame this difficulty with some success by build- ing up a charge of solid slabs perforated with holes, the object being to expose a minimum surface of powder at the commence- ment of combustion, and an increasing surface as the projectile moved up the bore of the gun. TGale Fie. 2. It was in accordance with this idea that the Black Prism powder was first made, and it needs no explanation to demonstrate that a charge of powder moulded to aregular shape, and of uniform size, must give more uniform results (ceteris paribus) than can be obtained by an equal weight of irregular grains or lumps. This modern-shaped powder, however, possesses other advantages of considerable import over the irregular P2 powder, which burns from surface to centre, and thus has a continually decreasing sur- face of combustion as the shot travels up the bore of the gun. The PRESIDENT’S ADDRESS—SECTION B. 99 perforated prisms, on the other hand, develop an increasing surface as it burns away, thereby keeping up a constant supply of speed- producing gas, and accelerating the speed of the projectile. In the P2 powder, therefore, we have actually a decreasing evolution of gas, whereas in the prism powder the order of things is reversed, as shown by the diagram.* In burning it is probable that the prisms break up across the lines of least resistance, as shown in Fig. 1., aa, 66, and so on, thereby producing many new surfaces for combustion and fully developing the progressive character of the powder. The prism form has been adhered to, but the Black Prismatic powder has been superseded by a still slower burning powder, which differs somewhat in composition from it in so far as it con- tains only 3 per cent. of sulphur and as much as 3 per cent. of moisture. It is known as 8.B.C, or slow burning ‘ Cocoa Powder.” This new form of prismatic powder brought about a complete revolution in gunuery. With aslower burning powder the lengthen- ing of the gun followed as a matter of course, the chambering was increased, and the muzzle loader was converted for obvious reasons into a breechloader. ‘* Cocoa powder”? may be looked upon as the connecting link between the obsolete black powder and the modern smokeless powders. Although it cannot be looked upon as a smokeless powder, in the latest sense of the term, yet the smoke produced by its combustion is white, and disperses very quickly. It is probable that the evidence of this, brought forward in experiments with heavy ordnance and quick-firing guns, served, in the first instance, to attract attention to the necessity of reducing the production of smoke to the least possible point, and finally led to the conviction among naval and military experts that the substitution of smokeless powder for black powder in artillery and small arms was a matter of the first importance. In accordance with this view, the energies of scientists, both at home and abroad, have, during the last few years, been devoted to the task of bringing this undertaking to a successfui issue. SMOKELESS POWDERS. Guncotton in every form, Pieric acid, and Nitro-cellulose, have, during the last twenty years, been subjected to experiment with the object of forming smokeless powders, but the problem, simple as it appears, presented almost insurmountable difficulties, and baffled the energies and knowledge of the most scientific chemists, so that it is only within the last few years that any approach to success has been made; and this success has been due to recent discoveries in chemistry. * Taken from ‘‘A Lecture delivered before the R.A. Institution on January 23rd, 1893,” by Lieut.-Col. F. W. J. Barker, R.A. 100 PRESIDENT’S ADDRESS—SECTION B. The following table gives the formula of—(1) Guncotton; (2) Nitro-glycerine ; and (3) Picric acid. For all practical purposes these may be considered the bases of all smokeless powders. (1) Guncotton.—Trinitro-cellulose, C,H; 0,3 (NO; ). obtained by the action of nitric acid upon cotton, thus :— C,H,0,3(HO) + 3 HNO, ) = C,H, 0, 3 (NO, ) + 3H, O. Cotton or Nitric Guncotton. Water. cellulose. acid. (2) Nitro-glycerine.—C 3H, 3 (NO; ), obtained by the action of nitric acid on glycerine. (3) Picric acid.—Trinitro-phenole, C, H; 3 (NO, ) O, formed by boiling carbolic acid or phenole and fuming nitric acid. As most of you are acquainted with the processes of the manu- facture of guncotton and nitro-glycerine, it will be unnecessary to describe them, but a few details referring to their properties may be of interest. Guncotton possesses totally different properties from gunpowder. Its temperature of ignition is from 250°-300° C. lower than that of gunpowder, but at this comparatively low temperature it burns away so rapidly that an experiment can be made on the palm of the hand without any fear of scorching it. For the same reason a piece of guncotton can be fired on a pile of gunpowder without the powder being ignited. It is easily detonated by means of a falling weight, but the explosion is confined to the portion struck. The pressure exerted by guncotton under the most favorable conditions has been estimated by Berthelot to be 160 tons to the square inch. The fact that all the products of the explosion of guncotton are gaseous renders it smokeless. Only 50 per cent. of the products of the ignition of gunpowder are gaseous. When wet it 1s absolutely uninflammable, but even when containing from 15 per cent. to 20 per cent. of water it can be detonated by the detonation of a dry primer of the same material. It presents many special advantages for its application in naval and military opera- tions; but as a smokeless powder it possesses one serious drawback, viz., it does not produce a satisfactory proportion of permanent gases during combustion, and, under certain circumstances, the violent local action of the explosive makes it, per se, unsuitable and highly dangerous as a propellant. Nitro-glycerine enters into the composition of a very important class of explosives possessing the generic title of ‘‘ dynamite.” When pure it is a colorless mobile liquid, of sp. gr. 1:6 at 15°5° C. When ignited in small quantities it burns slowly away, but when heated to the temperature of 188° C. it explodes with great violence. When spread in a thin layer it is extremely sensitive to slight con- cussion or blow. At a temperature of 4° C. it takes the crystalline form, and in this condition is far‘less sensitive to concussion or PRESIDENT’S ADDRESS—SECTION B. 101 blow than when in the liquid condition. Some idea of the ‘*power’’ of this explosive can be gathered from the fact that, under the most favorable conditions, 1 cub. foot of nitro-glycerine on explosion would expand to 10,006 cub. feet of gas in the short space of 5355 second. Picrie acid, which is largely used as a dye, was first investigated by Sprengel, in 1878, with regard to its properties as an explosive. Exhaustive experiments were carried out by Colonel Majendie, R.A., and Dr. Dupré, F.R.S., which went to show that picric acid could be readily detonated by so small a quantity as five grains of fulminate of mercury, and that such detonation would extend to picric acid containing over 14 per ‘cent. of water. In fact, when detonated, this acid behaves very much in the same way as com- pressed guncotton, as regards sensibility and the power of trans- mitting the initial detonation of the dry material to the same substance wetted. The products of the explosion of picric acid are gaseous, and consist of aqueous vapour and actively poisonous carbonic oxide. It is used in the manufacture of the French smokeless powder known as ‘“ Melinite.” The important discovery made a few years back by Mr. Alfred Nobel, that a certain kind of collodion cotton was soluble in nitro- glycerine, may be looked upon as the first step towards a new era in smokeless explosives. This new explosive, known as ‘“ Blasting Gelatine,” consisting of 90 per cent. of nitro-glycerine and 10 per cent. of collodion cotton, formed a very powerful compound, which, while suitable in an eminent degree for industrial purposes, was found to be too violent for Service purposes. The problem had yet to be solved, viz., how to tame this explosive, 7.e., to impart to it a sufficient energy for use in modern arms, combined with certainty and regularity of propulsion. To the unscientific mind this problem seemed easy of solution. The properties of guncotton were well understood; all that was required was a diluent or retarding agent, to slow down the violence of explosiveness; but the first approach to success was again due to the untiring perse- verance of Mr. Alfred Nobel, who found that guncotton could be incorporated with nitro-glycerine in equal proportions, and that when combined in such proportions an explosive was formed, even without the addition of any retarding agent, which was thoroughly reliable for Service purposes. It is a curious fact that two of the most violent explosives known, when combined, form a moderate explosive completely under control. The working out of this observation has led to the production of one of the most valuable of smokeless powders. ‘This powder, known as “ Ballistite’’ or **C/89,” consists of nitro-glycerine and guncotton, and is prepared in the following manner :— The nitro-glycerine and guncotton are placed in a vessel and the temperature raised by means of hot water, the contents being agitated until the whole mass has gelatinised. It is then placed 102 PRESIDENT’S ADDRESS—SECTION B. between rollers and rolled out into thin plates. These plates are cut into strips, and then into cubes, the thickness of the plates being regulated according to the purpose for which the powder is intended to be used. This powder has a horny, brownish-yellow appearance, and is so soft that it can be cut with a knife. The composition of ‘Cordite,’ the new English smokeless powder, though similar to is not identical with that of Ballistite. A committee of distinguished chemists in England, appointed by Government, determined after long investigations that the ingre- dients of Cordite should be as follows :— Guncottom,