128 



NATURE 



\yune 9, 1881 



out of 149 days on which the sun's disk was observed to 

 be free from spots, whilst in the preceding year there was 

 a complete absence of spots on 64 days out of 145. 



The spectroscopic observations of all kinds have been 

 completely reduced to 1S81, May 6. 



Touching the magnetical and meteorological in- 

 struments it was pointed out that the alterations 

 of the photographic cylinders of the m^ignetical and 

 meteorological instruments, which were in contem- 

 plation at the time of the last report, so as to 

 make their time-scales the same in extent and in position 

 on the record-sheets, have been to a great extent carried 

 out. In the case of the declination and horizontal force 

 magnets, two reflecting prisms with convex cylindrical 

 front surfaces have been mounted by Mr. Simms above 

 the registering cylinder, which has been lowered so that 

 each prism receives the light from the magnet opposite 

 to it. By this arrangement the traces of both magnets 

 fall (as regards time-scale) on the same part of the sheet. 

 The cylindrical lenses formerly used have been removed, 

 being replaced by the cylindrical surface of the prism. 

 The new arrangement is found to be perfectly satisfactory, 

 and Mr. Simms is proceeding with a similar change in 

 the case of the earth-current apparatus and of the vertical 

 force and barometer registers. 



A modification has been made in the system of deter- 

 mining the time-scales by the substitution of hourly breaks 

 in the register, for the photographed hour-lines. The 

 break at each hour is made automatically by a slight 

 alteration in the apparatus hitherto used for registering 

 the hour-lines. The time-scales for the declination, hori- 

 zontal force, vertical force, barometer, and electrometer 

 are now laid down in this way. 



The unsatisfactory state of the earth-current register 

 has been already noticed. After the change mentioned 

 in a preceding section, it was soon found that the indica- 

 tions of the earth-current wires were disturbed by a con- 

 tinual series of petty fluctuations which almost completely 

 masked the proper features of earth-currents. By cutting 

 off the communications with those parts of the wires 

 called the North Kent East Line and the Ladvwell Line 

 these disturbmces were checked ; but there remains a 

 periodic il disturbance at every hour, which entirely de- 

 stroys the value and credit of the results. It seems not 

 impossible that something may depend on imperfection of 

 earth-communication. If this fault cannot be removed, 

 the Astronomer-Royal proposes to return to the original 

 system of independent wires (formerly to Croydon ani 

 Dartford). 



The new pressure plate of Osier's anemometer has 

 worked well. The limiting pressure of fifty pounds on 

 the square foot was twice exceeded during the snow-storm 

 of iSSi, January 18. 



The photographic records of the measures of magnetic 

 earth-currents, in two directions upon the earth's surface 

 nearly at right angles to each other, are maintainei with the 

 same regularity as those of the ordinary magnetic forces, 

 and are preserved in readiness for reference or publication 

 when need may require. An extensive confederacy is 

 now organised, principally in Germanv, for register of the 

 earth-currents at several stations. 



The following are the principal results for magnetic 

 elements in the year 1880: — 



Approximate mean westerly de- 

 clination 



18' ^2' 



Mean horizontal force 



/3'9I2 (in English units). 

 ■ \ I '804 (in 1 



1 metric units). 



I 67 34 55 (by 9 inch needh-s). 



M'^andip ] 67 35 53 (:,y 6-inch needle.). 



' 67 36 3 (by 3-inch needles). 

 The report proceeds : — 



" In respect of diurnal inequalities of magnetic hori- 

 zontal force and its direction, though all measures are 



ready, the curves are not yet actually formed. In the 

 last report I advened to the usual character of these 

 curves. Assuming it to be certain that they originate 

 from the sun's power, not immediately, but mediately 

 through his action on the earth, it appears to me (as I 

 suggested long ago) that they are the effects of the 

 attraction of the red end or north end of the needle by 

 the heated portions of our globe, especially by the heated 

 sea, whose efiect appears to predominate greatly over that 

 of the land. I do not say that everything is thus made 

 perfectly clear, but I think that the leading phenomena 

 may be thus explained. And this is almost necessarily 

 the way of beginning a science." 



The number of hours of bright sunshine, recorded with 

 Campbell's Sunshine Instrument, during 1880, was 1214, 

 which is about the same as the average of the four years 

 for which we have a record. 



The discussion of the electrometer results for the year 

 1879 shows that the potential of the atmosphere is usually 

 positive ; that it is least in summer and greatest in winter, 

 and especially in the colder weather of winter. There is 

 also a definite diurnal inequality, having double maxima 

 and minima, the maxima, on the average of the year, 

 occurring at about 8h. a.m. and p.m. and the minima at 

 about 3h. a.m. and p.m. In character the diurnal curve 

 has a resemblance to the barometric curve, but the points 

 of maxima and minima precede those of the barometric 

 cui-ve by about two hours. On days of magnetic distur'o- 

 ance, when aurora is visible, nothing unusual is remarked 

 in the electrometer indications. Excepting thunderstorms 

 the greatest disturbances are experienced in showery 

 weather, and are probably local disturbances only. 



The time work is thus referred to : — 



" In the first few years after the strict and systematic 

 examination of competitive chronometers, beginning with 

 1856, the accuracy of chrono neters was greatly increased. 

 For many years past it has been nearly stationary. I 

 interpret this as showing that the effects of bad work- 

 manship are almost eliminated, and that future improve- 

 ment must be sought in change of some points of con- 

 struction. One which occurs to me (1 mention it princi- 

 pally as a specimen of departure from customary forms) 

 is this. The impact of the escape-wheel upon the pallet 

 of the balance-axis takes place very near to that axis, and 

 must produce considerable friction, though of short dura- 

 tion. I proposed to the late Mr. Charles Frodsham to 

 meet this by use of a broader pallet and a lighter impact 

 of longer duration. The decease of that accomplished 

 horologist prevented the completion of the trials which he 

 had commenced for carrying out my suggestion. Other 

 variations of the established form might be worthy of 

 trial. 



"Tiie Greenwich time-ball has been regularly dropped 

 automatically at ih. on every day throughout the year, 

 with the exception of 6 days when the violence of the 

 wind made it imprudent to raise the ball, and 8 days when 

 t ic severe frost of last winter prevented its being raised ; 

 and of one day when there was accidental faihire. 



" The Deal ball was not raised (on account of high 

 wind) on 10 days. It was not dropped (through failure 

 in the telegraphic connection) on 7 days, and was errone- 

 ously dropped about 5s. too soon by telegraph signals on 

 one day ; and on another day it was not dropped at ih. 

 owing to telegraph signals continuing up to ih. ; on one 

 day the current was too wea'^: to release the trigger. On 

 every other day the ball has been dropped automatically 

 at ih. 



"As regards the Westminster clock, its errors have 

 been under is. on 31 per cent, of the days of observation, 

 between is. and 2s on 47 per cent., between 2s. and 3s. on 

 18 per cent., and between 33. and 4s. on 4 per cent. 



'■The distribution of time-signals to all parts of the 

 country continues to be made on the same system as in 

 late years, by means of the chronopher at the central 



