June 8, 1893] 



NA TURE 



129 



mounted on stand No. 3, which was simply placed on the 

 floor and found sufficiently steady. From this position it 

 was possible to photograph the sun during about two 

 hours each day. 



In the year ending May 10, 1893, photographs of the 

 sun have been taken with this instrument on 180 days, 

 and of these 410 have been selected for preservation, 

 besides twenty-two photographs with double images of 

 the sun for determination of zero of position. 



The photographic telescope has been in regular use as 

 a photoheliograph since January, 1893, and photographs 

 of the sun have been obtained with it on eighty-nine days, 

 of which 158 have been selected for preservation. In all, 

 with one photoheliograph or the other, a record of the 

 state of the solar surface has been secured on 220 days 

 during the year. A new enlarging lens by Messrs. Ross 

 and Co., which appears to be very free from distortion, 

 was fitted to the Thompson photoheliograph on December 

 13, and has been used regularly for the eight-inch photo- 

 graphs of the sun. Taking into account the India and 

 Mauritius photographs received from the Solar Physics 

 Committee, solar pictures for 362 out of 366 days are 

 available for measurement. The photographs show that 

 solar activity has throughout the past year been fully 

 maintained, the mean daily spotted area for the years 

 1890, 1 89 1, 1892, being 100, 566, and 1230 respectively. 



The great solar activity mentioned above has its re- 

 action also in the number of computers employed, for 

 the report says that to cope with this unexpectedly severe 

 sun-spot maximum it has been necessary to largely 

 increase the number of computers employed on this 

 work, and a further addition will probably be required, 

 if, as seems likely, the solar activity continues to in- 

 crease. 



With regard to the magnetic observations, the regis- 

 tration has been carried on as in former years, the new 

 photographic processes recording with clearness and 

 delicacy many rapid magnetic movements that occur 

 during magnetic storms. 



The disturbance of the earth current registers due to 

 the trains running on the City and South London Electric 

 Railway still continues, and is of about the same magni- 

 tude as before. The substitution of a non-magnetic 

 silver pointer for the upper magnetic needle in the 

 galvanometers for the earth current apparatus, as men- 

 tioned in the last report, has proved very successful, the 

 scale values, which used to vary considerably, having 

 since remained remarkably constant. 



In view of the approaching introduction of a dynamo 

 into the Observatory grounds for electric lighting, experi- 

 ments have been made to determine the possible effect 

 on the magnetographs of the dynamo unshielded and 

 with triple iron shield. These experiments were carried 

 out at Messrs. Johnson and Phillips's factory, Charlton, 

 the deflection of the declination magnet of the portable 

 unifilar magnetometer being observed at distances of 20 

 and 40 feet respectively due west (magnetic) of the 

 dynamo, the poles of which were in the east and west 

 direction (magnetic), thus giving the maximum deflecting 

 effect. At the Royal Observatory the poles of the dynamo 

 will be north and south (astronomical), and it will be 

 placed at a distance of about 170 feet from the magnets 

 and nearly due south (magnetic). Making due allowance 

 for this, the experiments at Charlton would give the 

 following results : — 



Effect on Declination Magnet or y^°i'^l^^^,, 



00008 



Dynamo unshielded ... 

 Dynamo with triple shield 



4 

 o'-s 



the effect on the horizontal force magnet being expressed 

 in parts of the whole horizontal force. The corresponding 

 displacements of the magnetograph registers would be 

 only i/2oooth of an inch for declination and l/400th of 



NO. 1232, VOL. 48] 



an inch for horizontal force, in each case with triple 

 shield to the dynamo. 



The following are the principal results for the magnetic 

 elements for 1892 : — 



Mean declination (approximate) '7° ? 8' west 



Mean horizontal force 



Mean dip 



f 3 -961 3 (in British units) 

 \ I '8265 (in metric units) 

 ("67° 1 8' 42" (by 9-inch needles) 

 \ 67° 19' 45" (by 6-inch needles) 

 \(>t~' z\' 7" (by 3-inch needles) 



Meteorological observations have been continuously 

 maintained during the past year, and the reductions are 

 in the following state : — 



The observations of barometer, thermometers, anemo- 

 meters, rain-gauges, and sunshine-recorder (corrected, 

 where necessary, for instrumental error) are reduced up 

 to the present time. On the photographic sheets all the 

 time-scales are laid down, and the hourly ordinates are 

 read out for the dry and wet bulb thermometers to the 

 end of the year 1892, and for electrometer to the end of 

 July 1892. The table of principal changes in the direction 

 of the wind for 1892 is complete. ^ 



The mean temperature of the year 1892 was 48 -i, 

 being i°-4 below the average of the 50 years, 1841-1890. 

 The highest air temperature in the shade was 85 -9 on 

 June 10, and the lowest I7"6 on December 27. The 

 mean monthly temperature in 1892 was below the average 

 in all months excepting May, August, and November. 

 In March it was below the average by 4°-4, in October 

 by 4°'6, and in December by 3~'o. 



The mean daily motion of the air in 1 892 was 265 

 miles, being 17 miles below the average of the preceding 

 25 years. The greatest daily motion was 687 miles on 

 January 29, and the least, 48 miles on December 28. The 

 greatest pressure registered was ir8 lbs. on the square 

 foot on October 9. 



Bright sunshine was recorded on 1277 hours during 

 the year, this being 7 hours below the average of the pre- 

 ceding 15 years. The sun being above the horizon for 

 4465 hours, the mean proportion of sunshine for the year 

 was 0286, constant sunshine being represented by unity. 

 The rainfall amounted to 22-3 inches in 1892, this being 

 2'2 inches below the average of the fifty years 1841-1890. 

 In the determination of the longitude of Paris, four obser- 

 vers, two French and two English, took part in the work, 

 as in 1 888 ; three of them were the same as before 

 (Colonel Bassot, Commandant Defforges, and Mr. 

 Turner), but Mr. Hollis replaced Mr. Lewis, whose special 

 attention was required in the Time department. The 

 plan of operations adopted in 1888 was only modified in 

 the following particulars : two clocks were used instead 

 of one, at each end of the line, and all the clocks were 

 placed in rooms kept at nearly constant temperature. 

 The Sidereal Standard was used by the English observer 

 at Greenwich throughout. The English observers used 

 the small chronographs procured for the Montreal longi- 

 tude, with one pen only, thus avoiding the troublesome 

 correction for parallax of pens. 



In the Astronomer Royal's general remarks, he men- 

 tions that " the work of the Observatory during the past 

 year has been carried on under circumstances of excep- 

 tional difficulty. In the first place the operations for the 

 determination of the longitudes of Paris and Montreal 

 involved the absence of the Chief Assistant and of 

 another assistant for protracted periods during last 

 summer and autumn. Secondly, for six months the 

 Observatory was left entirely without the services of a 

 clerk, and the appointment of a permanent officer to 

 undertake cash and other clerical duties has not 

 yet been made ; thus the scientific work of the 

 Observatory has seriously suffered in consequence 

 It has not been possible for me, while harassed with 

 constant interruptions on matters of administrative 



