Nova Auriga. By E. E. Barnard, M.A. The first time I ever saw the object with the 36-inch was 1892 August 19. As soon as I saw it I was struck with the fact that it was really a very small nebula, "some 5" in diameter,' with a 10th-magnitude stellar nucleus. The nebulosity was very dense and whitish, and with a low power might escape notice. A setting of the wires gave the diameter of the nebulosity as 3". The star nucleus was from o'mi to om2 less than the star F of Mr. Burnham's diagram (Monthly Notices, vol. lii., No. 6). But with low power, as a whole, the nebula and nucleus were brighter than that star. At every observation since the nebulosity has been a striking object-the colour of nebula and nucleus being a bluish white-quite in contrast to the star F, which has appeared slightly yellow. The light seems to have been declining very slowly, At the last observation, October 23, the nucleus was fully one magnitude less than F, and the nebulosity seemed less bright and was smaller in extent. The bluish-white colour was still strikingly marked. To detect any motion perpendicular to the line of sight I have repeated Mr. Burnham's measures of last spring with two of his stars, so selected as to show motion if it existed. Here are the observations, all made with the micrometer of the 36-inch: Mr. Burnham's measures of the same stars are :— A comparison of these measures do not show with certainty any motion in A. But the distance A E seems to be increasing. If this is real, and it seems to be so, it is strange that before my observations, it is not apparent, as compared with those of Mr. Burnham. Measures will be made to decide whether this motion is real, and if so, as to whether it is in A or E. Mount Hamilton : 1892 October 24. Discovery of a Comet by Photography. By E. E. Barnard, M.A. On October 12 I made an exposure on the Milky Way near and west of a Aquila of 4 hours 20 minutes' duration with the Willard lens. Upon developing the plate I found a distinct hazy trail near the middle of it, and about a quarter of a degree long. By this time the position of the object was too near the horizon to make a search for it. The next night (13th), as soon as it was dark enough, a search was made with the 12-inch, and the object was found nearly a degree south-east of the position on the photograph. A few minutes' observation showed it to be a comet in motion to the south-east. The comet was very faint in the 12-inch, about the thirteenth magnitude, round, and but little brighter in the middle. It has been carefully observed at every opportunity since. This object is an exact representative of Class I. of shortperiod comets, very much resembling in appearance D'Arrest's comet. The micrometer position on October 13 was 1892 October 13d 7h 12m 29s Mount Hamilton M.T. App. 8= = +12° 30′ 5":0 From the faintness of the comet in the telescope, and the strength of its trail in the plate, it is evident that its light is mainly actinic. The plate used was a Cramer "Lightning," a very rapid and fine plate. Mount Hamilton: 1892 October 24. Note on the Period and Distance of the Fifth Satellite of Jupiter. By E. E. Barnard, M.A. This satellite was discovered here by the writer at midnight, 1892, September 9, with the 36-inch equatoreal. From the eastern elongations of September 10 and October 21 the following periodic time results: 11h 57m 20.5. Hourly motion 30° III. The period of 17h 36m distributed in Europe was an error in telegraphic transmission. The period of 11h 50m sent later was erroneously derived from the observed distances of the satellite. From seven eastern observed elongations the distance of the satellite (at east elongation) is 48" 094 (at 5.20). This corresponds to a distance from Jupiter's centre of 112,510 miles. The few observed western elongations give a distance about I" less than this, and there is evidently sensible ellipticity to the orbit. At present the satellite is assumed to be of the 13th magnitude. Under the most favourable conditions it has not been possible to see the shadow of this object when in transit. From these and other considerations the satellite is probably not over 100 miles in diameter. Taking everything into consideration the brightness at east and west elongations is the same. Mount Hamilton: 1892 October 24. P.S.-Following are two of the last observed east elongations of the satellite : 1892. d h m : Oct. 21 17 2.8 G.M.T. computed from measures before and after elongation. The measured distance at east elongation of the 23rd was October 26. 62" 90 On the Sidereal Period of the New Satellite of Jupiter. Upon examination of Professor E. E. Barnard's most important paper upon the "Discovery and Observation of a Fifth Satellite of Jupiter," published in No. 275 of the Astronomical Journal, for October 4, 1892, it seems probable that an error has been made in deducing the period from the concluded apparent distances of the satellite at its elongations, September 10, 12, and 14. Professor Barnard employs the formula— in which he states that m is the mass of the Earth, and M that of Jupiter, p and r the periodic time and geocentric radius of our Moon, P and R the periodic time and jovicentric radius of the new satellite. But, if he had desired to compare the period with that of our Moon, he ought to have employed the formula, in which m1 = m (nearly) is the mass of the Moon, and m。 is the mass of the new satellite, so small as to be neglected in comparison with the mass of Jupiter. Unless, therefore, the mass of the Earth meant by Mr. Barnard includes that of the Moon also, his resulting period is manifestly and decidedly too small. I prefer to compare the motion of the new satellite with that of the first hitherto known satellite of Jupiter. The exact formula to be employed is where M is the mass of Jupiter, mo and m, the masses of the new and first satellites, R and R, their jovicentric radii. We can, however, safely neglect the masses of both satellites, and use the simple expression From Barnard's apparent elongations, September 10, 12, 14, viz.: 6104, 61"55, 61"50, which correspond to G.M.T. 20h 53m, 20h 38m, 20h 24m (with sufficient accuracy), on the respective dates, I find by multiplying the apparent elongations in seconds of arc by the concluded geocentric radii of Jupiter, taken from the Nautical Almanac, and dividing by 5'202800, the heliocentric mean radius of Jupiter, that 47" 9613, 48" 1666, 48" 0217 are the corresponding elongations of the new satellite as viewed from the Sun at the mean distance of Jupiter on September 10, 12, 14. The mean of these three is 48′′ 04993. Now Bessel and Schur have given 111" 7360 and 1116523 for the mean elongation of Sat. I. of 2, at 2's mean distance from the Sun. The mean of these two measures is III" 6942. Moreover, the mean sidereal period of Sat. I. is 1.7691378 mean solar days. Hence we have as the sidereal period of the new satellite. It is remarkable that this differs little from 11h 59m, the period which is accepted by Mr. S. W. Burnham in a communication to the Chicago Academy of Sciences, at their meeting, 1892 October 4. (See Observatory, 1892 November.) Further measures of elongation distances will no doubt soon be published by Mr. Barnard, and may be used to correct the period found above. Murston Rectory: 1892 November 9. Addendum. Taking the necessary data from Professor W. Harkness's The Solar Parallax and the Related Constants, and employing the second formula in the foregoing paper, I find— An error of eventh of a second of arc in the assumed distance 4805 makes an appreciable difference in the resulting period. The best way of obtaining the true result is to infer it from the number of revolutions and parts of a revolution made by the satellite between the times of two distant elongations, as has now been done by Mr. A. Marth and Professor Barnard, whose periods thereby derived agree within half a second of time. The period found by Mr. Marth is 11h 57m.33. 1892 November 15. Enlarged Star and Moon Photographs. By H. C. Russell, In making another enlargement of the photograph of the stars and nebulae about n Argus to replace the one destroyed in transit, it seems desirable to make it upon the same scale as Herschel's beautiful picture of that object published in the Cape observations, thus ensuring convenient comparison. This involved enlarging the original photograph, the scale of which is 2-3 ins. to 1°, up to 15 ins. to 1°, and the result is a strong testimony to the quality of the original negative. I have sent both positive and negative on paper. The paper negative of course involved making a positive by contact printing, in which much detail is lost. A comparison of these photographic enlargements with Herschel's drawing is very suggestive, both in regard to the difference in delineation and extent of the nebula by the eye and the sensitive plate, particularly in the great mass of detail which the camera brings out in the denser parts, and also the vastly greater number of stars, probably ten times as many in the photograph as in the drawing. (The original negative was exposed 5 hours.) I send also an enlargement of the same object (n Argus) from a negative taken with a 6-inch diameter Dallmeyer portrait lens, and 8 hours exposure, on a scale of 0'556 in. 1o, enlarged to 3 ins. = 1o. This enormously extends the area of the nebula, and shows that the dark markings which begin at the centre of the mass extend in curiously meandering lines to great distances, in several places enclosing nearly circular spaces. Looking at this photograph the nebula seems to spread out almost without limit, as indicated by the dark lanes which bring it into prominence; but the more definite parts, about which the connection with the central mass cannot be doubted, Cover a space measured by 2° in R.A. and 3° in Decl., while the photograph taken with the star camera and 5 hours' = |