June ii, 1891] 



NATURE 



129 



for the Museum was commenced at the beginning of 

 March. In consequence of a recent decision of the 

 Admiralty to largely increase the number of chrono- 

 meters and deck watches for the Navy, additional 

 accommodation for chronometers is required imme- 

 diately, the space in the present chronometer room being 

 insufficient even for existing requirements. 



In other directions the difficulty of providing in the 

 existing Observatory buildings for the accommodation of 

 the increasing staff and of the accumulating material is 

 severely felt, and it is very desirable that the pressure on 

 the space available should now be relieved by means of 

 a comprehensive scheme, which would supply a suitable 

 fireproof brick building to replace the wooden sheds and 

 huts which now disfigure the Observatory grounds, and 

 to provide for the expansion which has taken place in late 

 years, and which may be expected to continue in the future. 



To provide for the efficient working of the 28-inch 

 refractor about to be iiiounted on the south-east equa- 

 torial, the Admiralty have authorized the construction 

 of a new iron-framed dome, 36 feet in diameter, to be 

 erected on the south-east tower in place of the ex- 

 isting wooden drum, which, as mentioned in the last 

 Report, has been so much strained in the course of thirty 

 years, that there is great difficulty in turning it. An 

 attempt was made to render the existing dome more 

 serviceable by bolting the framework together more 

 thoroughly, and by substituting properly turned spheres 

 for the cannon-balls, but though the dome is not now 

 liable to stick fast as formerly, it is still very difficult 

 to turn, and cannot be considered serviceable. The new 

 36-foot dome, which is being constructed by Messrs. T. 

 Cooke and Sons, is of peculiar form, adapted to the 

 conditions of the case, the diameter being greater than 

 that of the tower on which it is erected. 



A photographic telescope with 9-inch object-glass by 

 Grubb, and a prism of 9 inches diameter by Hilger, have 

 been generously presented to the Royal Observatory by 

 Sir Henry Thompson. The telescope has been mounted 

 on the Lassell telescope as a photoheliograph, to give 

 8-inch pictures of the sun ; a camera with Dallmeyer 

 doublet (from photoheliograph No. 4), and an exposing 

 shutter, specially designed to give very short exposures, 

 being attached to it. 



Six more electric hand lamps and an Ampere gauge 

 (Sir W. Thomson's) have been purchased. 



In view of the advantage resulting from the use of 

 electric lighting for the photographic equatorial and for 

 other instruments, the Astronomer-Royal considers it 

 very desirable that an electric light installation should 

 be provided for the Observatory, so that this method of 

 lighting, which is specially adapted to the requirements 

 of an observatory, may be applied to the instruments 

 generally. The system now m use, of charging storage 

 cells from primary batteries, is necessarily extravagant, 

 and it does not admit of the desired extension. 



With regard to the work done, the following statement 

 shows the number of observations made with the transit- 

 circle in the year ending May 10, 1891 : — 



Transits, the separate limbs being counted as 

 separate observations 



Determinations of coUimation error 



Determinations of level error 



Circle observations 



Determinations of nadir point (included in the 



number of circle observations 387 



Reflection observations of stars (similarly included) 593 



For determining the variation of personal equation 



with the magnitude of the star, 324 transits, not included j 



in the above, have been observed. The apparent magni- | 



tudes of the stars are altered by placing a wire gauze j 



screen in front of the object-glass of the telescope, and | 



part of a transit is observed with clear aperture, part : 

 with obscured. The comparison of the two results gives 



6036 

 307 

 390 



5789 



the difference of personal equation for a definite change 

 of magnitude. It appears that all the four regular ob- 

 servers record the times of faint stars later than bright, 

 the difference per magnitude being about o^ois. 



Altazimuth. — The total number of observations made 

 in the year ending May 10, 1891, is as follows: — 



Azimuths of the moon and stars 



Azimuths of Mark I 



Azimuths of Mark II 



Zenith distances of the moon 

 Zenith distances of Mark I. 

 Zenith distances of Mark II. 



253 

 123 



193 

 118 

 124 

 188 



Reflex Zenith Tube.—^Anze. the date of the last Re- 

 port, 14 double observations of y Draconis have been 

 made and completely reduced to the end of 1890. M. 

 Lcewy's recent work seems to show that the determina- 

 tion of the constant of aberration with this instrument is 

 more trustworthy than had been supposed ; though the 

 circumstance that the observations give a negative 

 parallax for y Draconis suggests that there is some 

 unexplamed source of error. 



Sir H. Grubb reports that the object-glass and tube of 

 the 28-inch refractor are now practically ready for 

 mounting ; but the Astronomer-Royal proposes to delay 

 this operation until the completion of the new dome on 

 the south-east tower mentioned in the first section of this 

 Report. 



Work with the 13-inch photographic refractor was 

 seriously delayed by the accident to the driving-clock, 

 and, later, by the illness of Mr. Criswick ; but 81 stellar 

 photographs have been taken, all of which must be re- 

 garded as more or less experimental. Ferrous oxalate 

 development was used throughout, and all the plates were 

 photographically impressed with the reseau kindly sup- 

 plied by Prof. Vogel. The exposures have varied from 

 a few seconds to about an hour ; and trails have been 

 taken both on the equator and near the pole to test the 

 adjustment for orientation. Several different kinds of 

 plates have been used, including Cramer, Seed, Paget, 

 Star, Mawson and Swan, and Ilford ; and on the whole the 

 choice seems to lie between the Star and the Ilford plates. 



Spectroscopic and Photographic Observations. — For 

 determination of motions of approach or recession of 

 stars, 286 measures have been made of the displacement 

 of the F' line in the spectra of 31 stars, and 14 of the 

 'b line in the spectra of 6 stars, besides comparisons with 

 the spectra of Mars, the moon, the sun, or the sky, as a 

 check on the general accuracy of the results. The series 

 of observations with the l2f-inch refractor is now prac- 

 tically completed, and the results are under discussion. 

 An examination of those for the 21 stars most frequently 

 observed shows that there is a systematic error depend- 

 ing on the hour angle, thus necessitating a correction for 

 the position of the spectroscope at the observation. 



In the year ending May 10, 1891, photographs of the 

 sun have been taken at Greenwich on 224 days, and of 

 these, 483 have been selected for preservation, besides 

 18 photographs with double images of the sun for deter- 

 mination of zero of position. 



Magnetic Observations. — The following are the prin- 

 cipal results for the magnetic elements for 1890 : — 



Mean declination 

 Mean horizontal force 



Mean dip 



17° 28'-6 W. 

 / 3*9546 (in British units). 

 \ I '8234 (in metric units). 



O / II 



( 67 21 19 (by 9-inch needles). 

 < 67 22 53 (by 6-inch needles). 

 ( 67 24 24 (by 3-inch needles). 



Meteorological Observations. — The continuous regis- 

 tration of meteorological phenomena has been maintained 

 without interruption, except for four days in February 

 when the old thermograph and shed in the magnetic 

 ground were dismounted, and the new thermograph and 



NO. II 28, VOL. 44] 



