l82 



NATURE 



{y-ime 21, 1887 



II. Instruments, — As a matter of practical convenience, 

 portions of both the equatorial instruments have been 

 within the last day or two placed in the hands of the 

 opticians, with a view to modifications or repairs which 

 shall render them applicable to the entirely new de- 

 parture which is now in progress in respect of the 

 processes and methods of practical astronomy. The 

 De la Rue equatorial, which has long possessed an 

 historical value, has been rehabilitated mainly at the 

 expense of Dr. De la Rue in certain of its more delicate 

 working parts, and this has been so advantageously com- 

 pleted that Dr. De la Rue has been induced to introduce 

 still further renovations, whereby that instrument will be 

 placed in a condition probably equal to that in which it 

 first left its designers hands. 



The mounting of the large equatorial refractor, ori- 

 ginally supplied at the expense of the University, is now 

 required for some experimental inquiries suggested by 

 the Photographic Committee of the Royal Society. Dr. 

 De la Rue has supplied two mirrors of 15 inches aperture 

 of different focal length, and these are to be mounted 

 alternately on the tube of the refractor, together with a 

 camera as arranged by Mr. Grubb. The expense of these 

 valuable additions is borne by the Royal Society and 

 by Dr. De la Rue. The delicacy of the projected 

 inquiries necessitates the electrical control of the driving- 

 clock. 



The transit-circle recently presented to the University 

 by Mr. Barclay has realized my expectations of its excel- 

 lence. I find it to be thoroughly stable, and sufficient for 

 all the purposes required, whether for University instruc- 

 tion or for accurate meridional observations. In the 

 latter respect it completes the Observatory equipment. 

 The electrical illumination of the circles and other neces- 

 sary parts has proved entirely successful, and the general 

 aspect of the instrument as it stands on its massive 

 piers is such as to suggest confidence. 



III. Buildings. — The fabric of the building and its 

 complicated roofs and domes are in excellent substantial 

 repair, and will require no outlay that I can foresee during 

 the present year. 



IV. Astronomical Work — The somewhat hazardous 

 enterprise of attempting for the first time in the history 

 of astronomy to obtain the distance of the fixed stars 

 from our earth by the aid of photography has been 

 attended with success. The final results of the investiga- 

 tion have been placed in my hands only during the 

 writing of this Report. The first observation was obtained 

 on May 26 of last year, and the last was effected on 

 May 31 of the present year. The intermediate computa- 

 tions were systematically continued during the interval. 

 They involved the reduction of no less than 30,000 

 bisections of star images, oi 330 photographic plates, 

 procured on 89 nights. Eight independent determinations 

 of the parallax of the two components of 61 Cygni resulted 

 from all this work, and these happily indicate a substan- 

 tial agreement between themselves, and afford other 

 necessary proof of reliability. 



By a happy coincidence, on the very day when the 

 final results of these investigations were evolved, I had 

 the pleasure of a visit from Her Majesty's Astronomer at 

 the Cape of Good Hope, a practical observer whose ex- 

 perience in parallactic investigations is probably unrivalled. 

 His remarks, after critical eximination of the entire work, 

 have encouraged and gratified me. Astronomical photo- 

 graphy is hereby placed on a secure basis as an efficient 

 and exact exponent of the highest form of astronomical 

 science. 



Simultaneously with these observations, similar work 

 has been in progress for the deterniination of the parallax 

 of \x. CassiopeitC and Polaris. These observations will 

 now be treated on a less laborious scale. Photographic 

 plates of the Pleiades have also been taken with the view 

 of obtaining the accurate relative positions of about one 



hundred stars therein. The necessary triangulations 

 have been commenced. 



I should say that the experimental investigations 

 required by the Photographic Committee of the Royal 

 Society originated in the necessity of ascertaining 

 what are the limits of accurate field obtainable from 

 mirrors of different focal lengths : the inquiry had distinct 

 reference to the questions which were open for discussion 

 at the recent Paris International Conference. I deeply 

 regret that I was unable to fulfil my intention of taking 

 part (as invited by Admiral Mouchez) in that important 

 meeting. 



V. Finance. — The funds granted by the University 

 have been sufficient, notwithstanding the continuous 

 activity, which requires a corresponding continuity of 

 outlay. This grant, hitherto triennial, expires on 

 December 31 ne.xt. If the Board of Visitors see fit to 

 request the University to continue this grant for five 

 years, it would assist me in undertaking, for the Univer- 

 sity, a share in the production of a photographic map of 

 the heavens, a valuable and extended class of work, 

 which under other circumstances I should not be justified 

 in contemplating. 



The details given above testify without further words of 

 mine to the unwearied perseverance and intelligence of 

 my two able assistants, Mr. Plummer and Mr. Jenkins. 



Prof. J. C. Adams has just presented the Report of pro- 

 ceedings in the Cambridge Observatory, from May 27, 

 1886, to May 26, 1887. From this Report we take the 

 following extracts : — 



The total number of observations made with the 

 transit-circle during this interval, for determinations of 

 right ascension and north polar distance, is 2253. 



These include 726 observations of clock stars made on 

 15 [ nights; 68 observations of Polaris at the upper 

 transit involving 169 circle readings, and 61 observations 

 at the lower transit involving 149 circle readings; 1331 

 observations of zone stars made on 88 nights ; and 67 

 observations of stars compared with the minor planet 

 Sappho. 



For instrumental adjustment, the nadir point was 

 observed 218 limes, the bisections of the declination wires 

 with their images being in every case made in two posi- 

 tions of the observer, on the north and south sides of the 

 tube respectively; the level and collimation errors were 

 each observed 217 times. 



At the request of Mr. Bryant, F.R.A.S., the planet 

 Sappho was compared with adjacent stars 70 times on 7 

 nights from January 12 to February 2, by means of the 

 Northumberland equatorial and square bar micrometer 

 for differences of right ascension and declination. Before 

 the end of February all the compared stars were re- 

 peatedly observed with the meridian circle ; and in addi- 

 tion to this 9 stars which had been compared elsewhere 

 with Sappho. 



State of the Reductions.— Tht true right ascensions are 

 obtained up to February 17, 1887, and the true north 

 polar distances to April 27, 1887. 



The mean right ascensions and north polar distances 

 for January i, of the standard stars are calculated to the 

 end of 1886, as are also nearly all the observations of stars 

 made in the present year for comparison with Sappho. 

 The mean R.A. and N.P.D. of the zone stars are similarly 

 reduced up to the end of iSSr. The right ascensions of 

 zone stars are reduced to the epoch 1875 as far as March 

 16, 1878, and the north polar distances to March 1880. 



The collection of the observations of the zone stars for 

 the Catalogue has been commenced. 



A fresh determination of the intervals of the right 

 ascension wires from 73 observations of Polaris, from 

 1885 November 17 to 1886 July 6, was completed on 

 July 12. As no change seems 'to have taken place in the 

 wires, the results were combined with those previously 



