Februarv 23, 1899] 



NA TURE 



399 



the U.S. President, strongly urged the foundation of a depot 

 for the charts and instruments necessary for the navy ; but it was 

 not until 1830 that consent was given to this, when Lieut. 

 Gouldsboro established one at Washington, the only astro- 

 nomical equipment being a 30-inch focus transit. Three years 

 later the contents were removed to a room about 14 feet square 

 on Capitol Hill. Here the equipment was increased by a 3J in. 

 transit, a Borda's circle, 3 ft. 6 in. focus achromatic, a portable 

 transit, and sidereal clock. Up to this time the work of the institu- 

 tion entirely consisted of such astronomical observations as were 

 necessary for the rating of chronometers. In 1S38 a new epoch 

 was entered upon by the instalment of Lieut. Gilliss, who 

 at once improved the equipment and commenced systematic 

 observations of the moon, eclipses and occultations, and also 

 began the determination of right ascensions of standard stars. 

 He soon reported to the Government that the housing of the 

 instruments and charts was unsafe, and asked for better accom- 

 modation. It was not until 1842, however, that this request 

 was acceded to, but in that year a Bill was passed voting 25,000 

 dollars for a new observatory. To prepare for it, Gillis visited 

 all the European observatories and gave orders for the best 

 instruments then available. The site selected was close to the 

 Potomac River, and about 100 feet above the water. 



In September 1S44, the new observatory was ready for use 

 with a line equipment of first-class instruments ; but, strange 

 enough, the man who had evolved the whole of the arrange- 

 ments, Lieut. Gillis, was not selected as superintendent, this 

 post being given to Lieut. Maury, who occupied the position 

 until i86i. During his incumbency the chronograph was in- 

 troduced into the observatory, and it is of interest to read that 

 for the use of a magnetic clock, fillet chronograph and cylinder 

 chronograph. Dr. Locke was in 1849 paid the sum of 10,000 

 dollars. ^Iaury's scheme of work was so wide that the reduc- 

 tions soon fell behind, and an enormous mass of work remained 

 unpublished when he left in 1S61. Gillis succeeded him, and 

 again infused new life into the place. He resumed the meridian 

 work, which had been almost neglected, and started to complete 

 the reductions of previous observations. In June 1S66, the 

 observatory was relieved of a great part of its labour by the 

 creation of the Hydrographic Office, which then took charge of 

 all the charts, chronometers, sextants, &c. Later on, however, 

 in 1883, most of this work came back to the institution. Daily 

 time signals were originated in August 1865, by Prof Harkness, 

 and were transmitted by hand until 1S79, when an automatic 

 distributor was installed. The large 26-inch object-glass was 

 received in 1S73. 



Magnetic observations had been started under Maury in 1845, 

 but no progress was made until 1S87, when a complete outfit 

 was provided for obtaining continuous photographic records of 

 all the magnetic elements. 



In 1893 the observatory was again removed to its present site 

 on Georgetown heights, 280 feet above the Potomac ; it covers 

 a circle having a radius of 1000 feet, and an area of about 

 70 acres. The principal work of the observatory is to carry 

 forward a continuous series of meridian observations of the sun, 

 moon, planets and ephemeris stars, which form the basis of the 

 requisitions of the navy. Other work, however, has by no 

 means been neglected, as is shown by the lengthy li.st of pub- 

 lished observations and discoveries in the article. It is signifi- 

 cant to notice that the magnetic observations have been entirely 

 suspended at the new observatory since the summer of 1S98, 

 the results being vitiated by the electric roads in the vicinity. 



Use of Telephoto Lens in Astronomy. — Dr. Rudolf 

 Steinheil, of the famous German firm of opticians, contributes to 

 theBHeisk J ourual of Photography {vo\. xlvi. p. 102) an article 

 discussing, from experimental data, the extent to which the tele- 

 photo combination may be useful to astronomers. For stellar 

 work he thinks it will be little used, as for delineating faint 

 objects it is unfitted on account of its relatively low speed, and 

 for successfully defining double stars, &c., it would necessarily 

 have to be of large aperture. For the planets it is scarcely 

 more fitted, the prolonged exposures necessary causing loss of 

 definition owing to inaccur.acies of following. The field of its 

 use for astronomical purposes will probably thus only include 

 the sun and moon. In the case of the moon the success will 

 depend on the degree of magnification required, as if this is 

 pushed too far the image becomes feeble, and the difticulties 

 due to the moon's motion in declination, which are not remedi- 

 able by using a driving-clock, render the result uncertain. With 

 the sun, however, all the difficulties encountered with other 



NO. 1530, VOL. 59J 



objects disappear, as the light available is sufficient to allow of 

 instantaneous exposures with the largest amplifications. This 

 Dr. Steinheil thinks will be the only permanent use of the tele- 

 photo lens for astronomical purposes, and l.e instances cases in 

 which photographs of sun-spots have been obtained measuring 

 7 mm. without sacrificing detail. 



Velocity of Meteors. — Prof. G. F. Fitzgerald writes in 

 the Astrophysical fotimal (vol. ix. p. 50, January 1899), 

 suggesting the preparation for attempting to determine the 

 velocity of the meteors during the next prominent showers. All 

 that is required is an arrangement whereby a toothed wheel may 

 be rotated in front of the camera lens during the exposure. The 

 motion must be uniform, and we must know the rate of rota- 

 tion and number of teeth on the wheel, and design these so that 

 there may be two or more eclipses during the passage of the 

 meteor across the field. Other methods of breaking up the 

 image are given, such as an oscillatory motion of the lens or 

 plate, or pointing the camera to a moving mirror ; but in all 

 these cases distortion of the star images would follow, and hence 

 the advantage of the simple eclipsing arrangement. 



It would probably be possible with some such arrangement as 

 that suggested, to determine the meteor velocity with sufficient 

 accuracy to show whether there is any sensible change due to the 

 resistance of the atmosphere. 



It is also evident that if two such cameras were employed at 

 stations a considerable distance apart, and the same meteor 

 caught by each, that the information given by the two would be 

 extremely valuable. 



THE FISHES OF THE NILE. 

 A MEMORANDUM regarding a proposed survey of the 

 -'"'- Nile, with the object of determining the species of fishes 

 inhabiting its waters, has been drawn up by Dr. John Anderson, 

 F. R.S., and is here printed in full, as it will interest all 

 biologists. We are informed that the scheme, as detailed in the 

 memorandum, has been sanctioned, and that Mr. W. Leonard 

 S. Loat has been appointed superintendent. The only modi- 

 fication which has been made in the scheme, as detailed in the 

 memorandum, affects the permanent use of a steam launch, as 

 there was a practical difficulty in procuring one. The occasional 

 use of a steam launch for trawling purposes will be available. 

 This slight departure will in no way interfere with the efficiency 

 of the survey. 



Lord Cromer, whom Dr. Anderson approached on this 

 subject in November last, has taken a most lively interest in 

 the scheme throughout. The subjoined memorandum was 

 drawn up at his request, and he has provided the funds necessary 

 for the accomplishment of the Survey. 



Our knowledge of the fishes of the Nile appears as yet to be 

 very imperfect. It may be said to have taken its origin in 1750, 

 when Hasselquist descriljed thirteen species found in the deltaic 

 area or in its immediate proximity. Since his time a number of 

 distinguished men, e.g. Forskdl, Geoffroy St.-Hilaire, Riippell 

 and others, have contributed by their observations personally 

 carried out on the banks of the river to make its fishes more and 

 more known. 



By far the most important addition to our knowledge of the 

 fishes of the Nile, after Hasselquist's day, was that made by 

 Geoft'roy St.-Hilaire in the " Description de I'Egypte," in which 

 twenty-nine species were described and figured. Between 1S29 

 and 1832, Riippell published two valuable contributions to the 

 subject. De Joannis, who accompanied an expedition to Luxor, 

 somewhere about 1S30-34, seems to have undertaken a careful 

 investigation of the fishes of that locality during his brief visit. 

 The value attached to his work rested largely on the fact that 

 his descriptions, which were published in 1S35, were illustrated 

 by figures of each species drawn and coloured from life; more- 

 over, he had not depended solely on the fishermen for his 

 material, as not a few of the species were of no economic use and 

 have not been rediscovered since. He described fourteen 

 species in all, nine of which were new to science. His paper 

 was supplemented by a li.st of all the known species of fishes 

 inhabiting the Nile, including lUippell's observations up to 1S32 ; 

 hence he enumerated fifty-three species. 



In 1837, the third contribution of Riippell appeared ; but he 

 was seemingly unaware of Joannis's researches at Luxor, and 

 consequently he mentioned only fifty-five in his summary of the 

 species then known to inhabit the river. The fishes collected 

 by Russegger in Egypt enabled Heckel,in 1847, to raise the 



