i54 



NA TURE 



\June 14, i 



Forty-one photographs have been taken of the Pleiades and 

 other objects with different exposures and in different parts of 

 the plate, 13 of these being on curved plates. In these ex- 

 periments the Sheepshanks refractor was used as directing 

 telescope, the image of a star being kept on its cross-wires 

 during the exposure of a plate by means of the slow 

 motions. The plates measure 6 inches x 6 inches, repre- 

 senting 5!° x 5f°, ani it is found that on the flat plates 

 the star images are sensibly circular to a distance of nearly 

 2° from the centre of the field, while micrometric measures of 

 these plates show that for some distance beyond this limit the 

 relative places of stars can still be measured with an accuracy 

 exceeding that of meridian observations, and with no sensible 

 systematic error depending on magnitude or duration of ex- 

 posure. Comparison of the results on flat and curved plates 

 respectively indicates that the advantages of using the latter are 

 doubtful. As the Dallmeyer object-glass is peculiar in having the 

 flint omVide, it was reversed in the cell in the course of the experi- 

 ment, and some photographs were taken with it in this position, 

 the flint being inside. It appeared on comparing the results that 

 a somewhat better field is obtained with the flint outside. A 

 photographic object-glass of 6 inches aperture and 6 feet focal 

 length, made by Sir H. Grubb for experiment, was mounted at 

 the end of Apiil in place of the 4-inch object-glass, and some 

 trial photographs of stars have been taken with it. 



Special arrangements were made for observing 00 

 cultations during the total eclipse of the moon on January 

 28, observers being stationed at nine instruments, but 

 clouds covered the moon almost continuously during 

 totality. Various devices were adopted with a view to 

 facilitating the observation in rapid succession of the 

 faint stars occulted during the eclipse. In the case of two 

 instruments the eye-piece was mounted excentrically at 

 the distance of the radius of the moon's image from the 

 axis, so that without disturbing the position of the tele- 

 scope any point of the limb could be brought into the 

 centre of the field. For setting the position-circles rapidly 

 in the dark, cardboard circles with notches at important 

 points or with the figures indicated with luminous paint, 

 were found very useful. 



The spectroscopic observations of motions of stars in the 

 line of sight have been continued. The recent obser- 

 vations of Algol confirm the previous results indicating 

 orbital motion, but further observations are required to 

 establish the fact. At the request of Mr. Lockyer, the 

 spectra of a Orionis, a Herculis, y Cassiopeia?, and jS Lyra; 

 have been examined on several occasions. 



That the daily record of the solar surface is gradually 

 getting more complete is clearly shown by what happened 

 in the year 1887, in which Greenwich photographs are 

 available on 188 days ; photographs from India or Mauritius 

 filled up the gaps in the series on 173 clays, thus making 

 a total of 361 days out of 365 on which photographs 

 have been measured in this year. 



The sun has been free from spots on 106 days in the 

 year 1887, and the areas of both spots and facute have 

 diminished since the date of the last Report. With the 

 exception of a fine group seen during three rotations in 

 May, June, and July, and of three other groups, one in 

 July and two in De^ ember, all of these being in the 

 southern hemisphere, there has been a complete ab- 

 sence of conspicuous spots. The entire spotted area has 

 rarely amounted to 1/20CO of the sun's visible hemi- 

 sphere, and the mean is less than one-sixth of that re- 

 corded in 1883, being intermediate between those for the 

 years 1875 an d 1876. 



In view of the diminution of the current work as the 

 minimum of sunspots approaches, the further discussion 

 of the results of former years has been commenced, and 

 arrangements have been made through the Solar Physics 

 Committee to complete the Greenwich results as far as 

 practicable by the measurement of photographs taken else- 

 where, particularly at Ely and Cambridge, U.S. From 

 the beginning of 1882 thephotographicrecordis practically 

 complete, the measurement of Indian photographs to fill 



up gaps in the Greenwich series having been under- 

 taken from December 22, 1881. The further discus- 

 sion of results has, therefore, been commenced from that 

 date, and the projected areas of spots (uncorrected for 

 foreshortening) have been formed to May 29, 1885, and 

 from the beginning of 1886 to the end of 1887. The 

 ledgers in which the areas and positions of the spots of a 

 group are collected and the mean area and position of 

 the group, deduced for each day and for the whole period 

 of visibility, have been formed for 1886 and 1887, and 

 their completion for the years 1882 to 1885 will now be 

 taken in hand. Two new forms have been prepared to 

 exhibit the distribution of spotted area on each day for 

 every degree of latitude and for every 10° of longitude, 

 mean results being taken for each rotation and for each 

 year. 



With regard to magnetic observations we read that 

 the only important change is the substitution, since 

 October last, of a wooden bar loaded with lead, of the 

 same size and weight as the declination-magnet, for the 

 brass bar hitherto used for determination of the torsion 

 of the suspending skein, a very weak trace of magnetism 

 having been detected in the brass bar. 



The earth-current observations have been attended with 

 some difficulties. We read : — 



The earth-current wire 5 , which were damaged by the snow- 

 storm of 1886 December 26, were not completely repaired till 

 August 1887, when it was found that the earth-plate at Angerstein 

 Wharf had been stolen, another earth-plate being then supplied. 

 A renewal of the earth-current wires concurrently with the 

 telegraph wires on this portion of the South-Eastern Railway 

 was arranged, in concert with Mr. Leonard, but this has not 

 been carried out owing to a rise in the price of copper. Five 

 measures of resistance of the earth-current wires have been made 

 since the last Report, but the results are not satisfactory, owing 

 presumably to the bad condition of the wires. On the line from 

 Angerstein Wharf to I.adywell, 7A miles in length, the measures 

 of resistance range from 220 10285 ohms, and on the Blackheath 

 to North Kent East Junction line, 5 miles long, the measures 

 range from 230 to 262 ohms. Under these circumstances it 

 seems hopeless to attempt to express the merures of ordinates 

 on the earth-current sheets in terms of the electrical units until 

 the conditions of the circuits have been improved A furthei 

 difficulty arises in discussing the small diurnal inequality on the 

 earth-current registers in consequence of the circumstance (to 

 which attention was first drawn by Mr. A. J. S. Adams, of the 

 Post Office Telegraphs) that there is a slight dislocation in the 

 Angerstein Wharf to Lady well traceshortly after sunset with sudden 

 return to the original position shortly before sunrise, representing 

 an increase! current from Lady well to Angerstein Wharf, or a 

 diminished potential at Angerstein Wharf during the night hours. 

 Possibly this may be connected with the electric lighting in the 

 vicinity of the earth plate. It appears to have commenced in 

 1883, becoming more pronounced in 1884. 



The following are the principal results for the magnetic 

 elements for 1887 : — 



Approximate mean declination . . 17 47 W. 



,, , . .,, f 3 '94IQ (in B itish units') 



Mean horizontal force . . | ?.{£ 7 J \ [n Metric units) 



I 67 25' 45" (by 9-inch needles 

 Mean dip . . . . j 67 26 20 (by 6-inch needles) 



( 67 27 13 (by 3-inch ne 



In the year 1887 there were only three days of great 

 magnetic disturbance, but there were also about twenty 

 other days of lesser disturbance for which tracings of the 

 photographic curves will be published, as well as tracings 

 of the registers on four typical quiet days. 



The mean daily motion of the air in 1887 was 275 miles, 

 being 9 miles below the average of the preceding twenty 

 years. The greatest daily motion was 829 miles on. 

 March 23 ; and the least, 59 miles on November 16. The 

 only recorded pressure exceeding 20 pounds on the square 

 foot was 2o - 5 pounds on April 6. 



