June 7 , 1883] 



NA TURE 



13/ 



" The investigation of personal equations has been completed 

 for the year lSS2, the results being very accordant with those 

 found in the preceding year. 



" The circle observations are completely reduced so as to 

 form mean X. P. D. for 1S83, January I to April 21, apparent 

 Z. D.'s being formed to April ;>:>. 



" From the beginning of this year a correction of -o""39 

 has been applied to the results of the nadir observation to make 

 them agree in the mean with the results of reflection ot servations of 

 stars. This correction has been deduced from a comparison of 

 the nadir results throughout 1S22 with corresponding reflection 

 results for stars north and south of the zenith. The discordance 

 appears to be increasing, and its source has not yet been traced. 

 It does not appear to originate on this occasion with the micro- 

 scope-micrometer or telescope-micrometer, and it is not con- 

 nected with the extension of the range of observation of stars 

 by reflection. The disc rdance, which was insignificant in 1S78, 

 amounting only to -o"o3, has gradually increased since, being 

 -o""loin 1879, -o" - 29 in 1880, -o"30 in 1881, -o"'39 in 

 l8S2, and for the first four months of this year — o"'5S. 



•' Determinations of flexure have been made on 1SS2, Decern- 

 l.er 30, and 1SS3, May 10 and iS, the resulting values being 

 -O '07 and -o" "78 and -0'33. The observations on May lS 

 were not altogether satisfactory, as the sun was shining during 

 the second set of measures. The values resulting from the first 

 and second sets respectively are -o""72 and +o"o5. There is 

 apparently nothing in the observations on May 10 to account 

 for the exceptionally large value found on that day. No correc- 

 tion for flexure, as apart from the correction for R - D, has been 

 applied to the observations. 



'• The correction for R - D, the error of assumed colatitude, 

 and the position of the ecliptic have been investigated for 18S2. 

 For the planetary results, errors of R.A. and N.P.D. have been 

 formed, but the heliocentric errors have not yet been computed. 



" The reflection observations of stars available for investiga- 

 tion of the R-D discordance extend from Z.D. 71 J c north to 

 Z. D. 7oJ° south, and the discussion of these shows discordances 

 steadily increasing from the zenith towards the horizon, and 

 amounting to - i"-s8 for the group at Z.D. 681" north and to 

 + l"'66 at Z.D. 70' south, a correction of + g"i6 sin Z.D. 

 having been first applied to the reflection observations for in- 

 clination of the vertical at the mercury trough. It is quite evi- 

 dent that the discordances do not follow any such law-, as a + b 

 sin ■ . cos 5 >, which was used from 1S62 to 1880. Assuming the 

 law a + l> sin :, which was adopted in the years preceding 1862 

 and in 18S1, the R - D correction for 18S2 would be +o"'07 

 + o"'42 sin .-, and for the sake of continuity in the sys- 

 tem of reductions this correction has been provisionally 

 adjp'ed for use in 1SS2. But the discordances between 

 this formula and the observed quantities increase regularly 

 from the zenith towards the horizon, amounting to half of 

 the observed quantities at Z. D. 50 3 to 60°. The formula 

 + o'oS + o"'29 tan a represents the observations better, 

 though even this does not give sufficiently Jarge results at large 

 zenith distances. In this discussion coi responding reflection 

 and direct observations made on the same day have alone been 

 u ed. 



" The value found for the colatitude from the observations of 

 1882 is 3S' 31' 21" 93, very slightly larger than the assumed 

 value ; the correction to the tabular obliquity of the ecliptic is 

 + o" 44 ; and the discordance between the results from the 

 summer and winter solstices is + o "37. 



' ' The mean error of the moon's tabular R. A. from observa- 

 tinns with the transit-circle in 18S2 is + oS2s. 



"The following observations have been made with the altazi- 

 muth from 1882, May 20, to 1883, May 20 : — 



Azimuths of the moon and stars 317 



Azimuths of the azimuth-mark 228 



Azimuths of the collimating-mark 216 



Zenith-distances of the moon 176 



Zenith-distances of the collimating-mark 214 



"Azimuths and zenith-distances of Comet b 1SS2 were 

 observed on a single day. 



"The altazimuth observations are completely reduced to 

 May 6, so as to exhibit errors of moon's tabular R.A., N.P.D., 

 longitude, and ecliptic N.P.D. The restriction of the observa- 

 tio .s, and the limitation of the computations to o-ois. and o""l 

 have made these reductions comparatively light. 



"The moon's diameter has been measured — 



With the transit-circle, twice in R.A., 17 times in N.P.D. 

 With the altazimuth, 4 times in azimuth, 10 times in Z.D. " 



On the subject of Equatoreals Mr. Christie states: — "A 

 very valuable addition has been made to the instruments of the 

 Royal Observatory by the gift of the Lassell two-feet reflecting 

 equatoreal, which has been generously presented by the Misses 

 Lassell. The exceptional qualities of this fine telescope (with 

 which Hyperion was discovered in 1848) are well known, and 

 there could be no hesitation in accepting on the part of the 

 Admiralty the offer of such a valuable gift. The instrument 

 was removed from Maidenhead early in March, and has been 

 erected in the south ground, where it commands a nearly unob- 

 structed view of the sky to within about 5' of the horizon. A 

 circular building 30 feet in diameter, has been erected for the 

 Lassell telescope, and the construction of a suitable dome is 

 authorised. There are two large mirrors available for use, and 

 I contemplate taking advantage of the firm m mnting and 

 perfect clock movement of the south-east equatoreal to mount 

 the spare minor on this instrument, attaching it to the tube of 

 the refractor, so as to have on the same mounting a refractor 

 and reflector with their axes t arallel. The former would be 

 available for eye observation, whilst the latter could be used on 

 the -ame object for physical work, spectroscopic or photo- 

 graphic. The Lassell telescope it- elf would be well suited for 

 observation of faint satellites and comets which are beyond our 

 present instrumental nfans. 



"The observations of the solar eclipse of 1SS2, May 17, with 

 the south-east equatoreal are completely reduced, and the final 

 equitions have been solved. 



"The spectroscopic observations during the past twelve 

 months have bee 1 somewhat restricted through the pressure of 

 the photographic reductions at a time of maximum of sunspot 

 frequency. The solar prominences have been ob-erved with the 

 half-prism spectroscope on eight days, and four sun-pots have 

 been examined on eight days with reference to the broadening 

 of lines in their spectra. The s| ectrum of the great spot of 

 1882, November 12-25, showed some remarkable reversals of 

 the lines of hydrogen and sodium, and an extraordinary displace- 

 ment of the F line. 



"As regards the determination of motions of stars in the line 

 of sight, 142 measures have been made of the displacement of 

 the 1 line in the si ectra of 23 stars, and 26 mea-ures of the *, 

 line in 9 stars. The 1 hservations of Sirius during the past 

 winter tend on the whole to confirm the impression that the rate 

 of recession of this star has diminished progre-sively since 1S77, 

 and that the motion is now on the point of being converted into 

 one of approach. 



"The spectrum of Comet a 18S2 was examined on three 

 nights, that of the great Comet * 18S2 on three nights, and 

 that of Comet a 1S83 on one night The spectrum of the first- 

 named object showed the yellow sodium lines with great bril- 

 liancy just before perihelion passage. The spectrum of the 

 aurora of 1882, November 17, was also examined. 



"The spectroscopic ob-ervations of all kinds have been com- 

 pletely reduced to 1SS3, May 20. 



"In the year ending I SS3, May 20, photographs of the sun 

 have been taken on 200 days, and of these 339 have been 

 selected for preservation. There were 7 days on which the 

 sun's disk was observed to be free from spots. The number and 

 size of sp >ts and facula: continued to increase in a marked way 

 tiU last November, when a group of spots of very unu-ual size 

 appearel. Since that date, however, the sun has become more 

 quiescent. 



" Since the beginning of December, gelatine dry plates have 

 been used instead of the old wet-plate process They are more 

 convenient in use, and appear to s;' ve as g 00<1 average results. 

 The photographs on a scale of 8 inches to the sun's diameter 

 recently obtained in India, under the auspices of the Solar 

 Physics Committee, are so successful that the Committee have 

 recommended the general adoption of this rcale, and I propose, 

 as soon as we have a spare photoheliograph returned from the 

 Eclipse Expedition, to have it altered in the same manner as the 

 Indian photoheliograph, so as to obtain eight-inch photographs 

 of the sun instead of four-inch. ^ 



" It was suggested in the last Repoit that the measurement of 

 such of the Indian and other photographs as w ere required to 

 fill up gaps in the Greenw ich series might with advantage be 

 undertaken here. This proposal has now been carried out, and 

 ill photographs for the period frjm 1881, December 22, to 

 18S2, October 19, have been received from the Solar Physics 



