154 



NATURE 



\yune 12, 1879 



The meridian observations of stars are directed primarily 

 to the determination, with the greatest attainable accuracy, 

 of the places of 215 fundamental stars observed through- 

 out the day and night, and these are supplemented by 

 observations of stars taken from a working catalogue of 

 about 2,500 stars. About 1,300 of these stars were ob- 

 served in 1878, forming a larger annual catalogue than 

 usual. 



As might have been expected, the Astronomer- Royal's 

 report on the weather of the past year is not satisfactory. 

 After a fine autumn, the weather in the past winter and 

 spring has been remarkably bad. More than an entire 

 lunation was lost with the transit-circle, no observation of 

 the moon on the meridian having been possible between 

 January 8 and March I, a period of more than seven 

 weeks. Neither sun nor stars were visible for eleven 

 days, during which period the clock-times were carried 

 on entirely by the preceding rate of the clock. The 

 accumulated error at the end of this time did not exceed 

 OS.-3. 



" During the past year, spectroscopic observations have 

 been almost entirely suspended, in order that the reduc- 

 tions of accumulated photographic observations might 

 proceed more rapidly. The sun's chromosphere has been 

 examined on seven days only, and, on five of these, 

 prominences were seen. Two measures of the displace- 

 ment of the F-line in the spectrum of a Virginis, and 26 

 of the b lines in the spectra of 6 stars (3 of them not 

 previously examined), as compared with the corresponding 

 lines of hydrogen and magnesium, have been made. In 

 five of these, though the stars were of the second 

 magnitude only, a dispersive power equivalent to fifteen 

 prisms of 60° was used. These observations were checked 

 by reference to the Y or b lines in the spectrum of the 

 moon or of the sky. The spectrum of Brorsen's comet 

 has been examined with the half-prism spectroscope, and 

 that of the eclipsed moon on 1868, August 12, with the 

 single-prism spectroscope. 



"Photographs of the sun have been taken on 150 days, 

 and 228 of these have been selected for preservation. 

 The photographs show a complete absence of spots on 

 121 days out of 150 ; and on comparing them with those 

 of the preceding year, when there was an absence of 

 spots on 66 days out of 156, it appears that we have not 

 yet passed the minimum. 



" The following are the principal results for mag^netic 

 elements in the year 1878 : — 



Approximate mean westerly 

 declination 



Mean horizontal force . . . 



Mean dip 



i8« 49'. 



3 '905 (in English units). 

 I "Sol (in Metric units). 



O I II 



67 37 10 (by 9-inch needles). 

 67 38 12 (by 6-inch needles). 

 67 38 59 (by 3-inch needles). 



" The magnetic reductions for the years 1865 to 1876 are 

 nearly completed. The results are exhibited in the form 

 of annual and monthly mean curves of diurnal inequality, 

 as in preceding investigations, the abscissa showing the 

 variation of magnetic declination, and the ordinates that 

 of horizontal force, throughout the twenty-four hours. 

 The annual curves of diurnal inequality are now complete 

 for the period of thirty-six years, from 1841 to 1876; and 

 from the great length of this series of observations," the 

 Astronomer-Royal goes on to say, " all made on the same 

 system and with similar instruments, most important 

 inferences may be drawn, both as to the laws of diurnal 

 inequality in general and its changes in different years 

 and seasons, and as to the connection between magnetic 

 phenomena and sun-spots. These annual curves show a 

 well-marked change in close correspondence with the 

 number of sun-spots. About the epoch of maximum of 

 sun-spots they are large and nearly circular, having the 



same character as the curves for the summer months ; 

 whilst about the time of sun-spot minimum they are small 

 and lemniscate-shaped, with a striking resemblance to 

 the curves for the winter months. We think with the 

 Astronomer- Royal that it may be worthy the considera- 

 tion of the Board whether the whole of these resuks, with 

 any modifications that experience suggests, should not be 

 printed and circulated as a separate volume. 



" The monthly curves, 1865-76, have been formed for 

 three periods of four years each, corresponding roughly 

 to periods of minimum, maximum, and mean of sun-spots, 

 and the whole series stands thus (the general character of 

 the curves being added) : — 1841-47 (curves) mean ; 1848- 

 57, small; 1858-63, large in summer, small in winter; 

 1865-68, small ; 1869-72, very large; 1873-76, mean. The 

 maxima of sun-spots occurred in 1848, i860, and 1870, 

 and the minima in 1844, 1856, and prolsably in 1879. 



" The connection between changes of terrestrial mag- 

 netism and sun-spots," the Astronomer- Royal states, 'is 

 shown in a still more striking manner by a comparison 

 which Mr. Ellis has made between the monthly means of 

 the diurnal range of declination and horizontal force, and 

 Dr. R. Wolf's "relative numbers" for frequency of sun- 

 spots. It appears from this that not only is there a 

 general correspondence in the two sets of phenomena, but 

 that the minor irregularities of the sun-spot curve are re- 

 produced in the curves of diurnal magnetic range ; and 

 further that the well-marked annual inequality in the 

 latter is itself variable, being greatest at the time of 

 maximum of sun-spots and least at that of minimum. It 

 will be an interesting inquiry, when sun-spots become 

 more numerous, to determine whether the present paucity 

 of earth-currents is connected with the fewness of spots." 



The Astronomer-Royal, by these researches, has en- 

 dorsed the work we owe to Sabine, Broun, Stewart, and 

 others. 



The Report states that the Westminster clock has not 

 been quite so well regulated as usual. During the period 

 to which this Report refers, its error exceeded is. on 77 

 days ; on 15 of these it was between 2S. and 3s., on 4 

 between 3s. and 4s., and on i day it exceeded 4s. 



With regard to the last Transit of Venus results, the 

 past year has been occupied in putting reports and calcu- 

 lations in a shape adapted to eventual printing of the 

 account of the whole enterprise. With regard to the 

 Transit of 1882, the Astronomer-Royal informs us that the 

 general impression appears to be that it will be best to 

 confine observations to simple telescopic observations 

 or mcirometer observations at ingress and egress, if 

 possible at places whose longitudes are known. For the 

 first phenomenon (accelerated ingress) the choice of 

 stations is not good ; but for the other phenomena (re. 

 tarded ingress, accelerated egress, retarded egress), there 

 appears to be no difficulty. The adoption of a south- 

 polar station seems to be practically abandoned. 



With regard to the numerical lunar theory, the Report 

 states that the incessant pressure of the business of the 

 observatory has prevented the Astronomer-Royal ad- 

 vancing so rapidly as he had hoped. " The solar per- 

 turbing forces are all computed to 10-7 in all cases, and 

 to icrS and 10-9 in those cases in which large factors are 

 introduced by theory as necessary for obtaining the cor- 

 rection to tabular coefficients from discordance of com- 

 puted deductions (lunar places on one side, with solar forces 

 on the other). The lunar places with the same argu- 

 ments, first computed to 10-7, are now extended to icrj or 

 10-9, for the powers of radius vector. The computations 

 of the same kind for the other assumed elements (longi- 

 tude and latitude) are not begun. In regard to the 

 discordance of annual equation, to which I called atten- 

 tion in the last Report, I suspend my judgment. I have 

 now discussed the theory completely ; and, in going into 

 details of secular changes, I am at this time engaged on 

 that which is the foundation of all, namely, the change of 



