[JUNE 8, 1899 
16° 39'°2 West. 
(with 3-inch needles). 
138 WNGAEOT IE 
For the For the declination, horizontal force, and dip have been made as in 
_Chart Catalogue former years. 
pec Seea ese On the completion of the new Magnetic Pavilion, last 
Number of photographs taken... 256 nah 200 September, the Gibson deflection instrument and the Airy dip- 
Be successful plates ae 211 as 167 circle were mounted there, and regular determinations of 
4 fields photographed suc- magnetic horizontal force and dip have been made there from 
cessfully et Ly siete lips deny p RZOOH Ack aetme LOO) that time, ; 
Total number of successful fields The principal results for the magnetic elements for 1898 are 
reported 1898 May 10... es $28 OF 909 as follows :— 
Nut ee ee Mean dectnation eae 
C " . sae . 
: , 3 eB . : 39878 (in British units). 
during the year... Sa sie 5 39 Mean horizontal force 18387 (in Metric units). 
._ { January to June 67° 12'-4) 
Total number of successful fields Mean dip/! re. aaa 
obtained to 1899 May 10 no HOR 1030 VOctober to Decetaber a7. 11:3) 
— These results depend on observations on the site of the 
Number still to be taken... eee 122 a0 119 Magnetic Pavilion, and are free from any disturbing effect of 
Of the 122 fields to be photographed, ror are within 7° of 
the pole. The photography of this part of the sky was purposely 
deferred till near the epoch 1goo, and has just been begun. 
In last year’s Report, we mentioned that 166 catalogue plates 
out of 909—that is, nearly one-fifth of the total number—and 
go chart-plates out of 828, had deteriorated owing, probably, 
to the effect of damp in the building in which they have to be 
stored pending the completion of the new physical laboratory. 
This year we read that the deterioration of some of the plates 
has continued, as it was not found practicable to move the 
photographs into the new Observatory building till March. 
Besides the plates which have been rejected during the year, as 
mentioned in the tabular statement above, there are about forty 
catalogue plates in the zones yet to be measured which should 
be takenagain. The damaged chart-plates have all been copied, 
and the positives on glass will in any case be available. But it 
seems advisable that all the damaged plates, whether measured 
or copied, should be replaced by others, and, as the photo- 
mapping for the zone allotted to Greenwich is now nearly 
completed, this work can shortly be taken in hand. 
Heliographic Observations. 
In the year ending 1899 May 10, photographs of the sun 
have been taken on 195 days, either with the Dallmeyer or 
Thompson photo-heliographs. The former, mounted on the 
terrace roof of the south wing of the physical observatory, was 
used as the regular instrument for solar photography up to and 
including 1898 July 27, when the Thompson 9-inch photo- 
heliograph was substituted for it. The Dallmeyer photo-helio- 
graph was dismounted and placed in the upper floor of the 
museum on 1898 October 13. Ot! the photographs taken with 
either instrument, 394 have been selected for preservation, 
besides sixteen photographs with double images of the sun, for 
determination of zero of position-angle. Photographs to 
supplement the Greenwich series have been received from India 
and Mauritius up to 1899 January 13. 
For the year 1898, Greenwich photographs have been selected 
for measurement on 165 days, and photographs from India and 
Mauritius (filling up the gaps in the series) on 192 days, making 
a total of 357 days out of 365 on which photographs are at 
present available. No photographs have been received from 
Mauritius of later date than 1898 August 7, and as the eight 
days which are at present unrepresented are all since that date, 
it is possible that the record for the year may yet be rendered 
complete. 
The chief incident in the history of the sun’s surface, during 
the period covered by this Report, was the very remarkable 
temporary revival of activity which set in at the end of July 
and lasted almost to the middle of November, culminating in 
the appearance of the great group of September 3-15. Apart 
from this, the sun’s surface has been very quiet during the year, 
the spots being few, isolated, and small. There have, however, 
been no such long-continued instances of the entire absence of 
spots as to suggest that the minimum had been actually reached 
or is immediately at hand, the number of days without spots 
for which a record is at present available being 49, as compared 
with 42 in the previous Report. 
Magnetic Observations. 
The variations of magnetic declination, horizontal torce, and 
vertical force, and of earth currents, have been registered photo- 
graphically, and accompanying eye observations of absolute 
NO. 1545, VOL. 60] 
iron. The correction to the declination, as found in the Magnet 
House, is —10''7, deduced from the observations with the 
Elliott declincmeter, in September and October, and with the 
new declinometer in the Magnetic Pavilion, the values found 
with the two instruments being precisely the same. 
The question of the protection of the Observatory from dis- 
turbance of the magnetic registers by electric railways or tram- 
ways in the neighbourhood has caused much anxiety during the 
past year. A number of such railways are now projected, and 
the value of the magnetic registers, which have now been 
carried on continuously for nearly sixty years, will depend 
entirely on the conditions under which electric traction is used. 
Steps have been taken, in concert with Prof. Riicker, acting on 
behalf of Kew Observatory, to have a special clause inserted for 
the protection of Greenwich and Kew Observatories. This has 
already been accepted in several cases, and it is hoped that it 
will be agreed to in others where necessary. 
Meteorological Observations. 
The mean temperature of the year 1898 was 51°°3, being 
1°°8 above the average for the fifty years 1841-1890. During 
the twelve months ending 1899 April 30, the highest daily 
temperature in the shade recorded in the open stand was 92°°1 
on September 8. The highest reading recorded in the 
Stevenson screen was 9o°‘0 on the same day. 
The monthly mean temperatures were in excess of their 
corresponding averages from August to February (inclusive) to 
the mean amount of 3°°9. In December, the excess amounted 
to 6°'1, and in September to 4°"9. In the five remaining 
months of the year the mean temperatures were below the 
average values. 
The mean daily horizontal movement of the air in the twelve 
months ending 1899 April 30 was 291 miles, which is ten miles 
above the average for the preceding thirty-one years. The 
greatest recorded movement was 950 miles on January 21, and 
the least 67 miles on March 14. The greatest recorded pressure 
of the wind was 33 lbs. on the square foot on February 13, and 
the greatest hourly velocity 53 miles on January 12. 
The number of hours of bright sunshine recorded during the 
twelve months ending 1899 April 30 by the Campbell-Stokes 
instrument was 1500 out of the 4454 hours during which the 
sun was above the horizon, so that the mean proportion of sun- 
shine for the year was 0°337, constant sunshine being repre- 
sented by 1. 
The rainfall for the year ending 1899 April 30 was 22°74 
inches, being 1°80 inches less than the average of fifty years. 
The number of rainy days was 158. The rainfall in the month of 
September amounted to 0°305 inch, being the smallest Sep- 
tember rainfall on record in the period 1841-98, with the ex- 
ception of September 1865, when the rainfall was only 0°16 
inch, : 
Longitude of Killorglin. 
The longitude of Killorglin, at the head of Dingle Bay, 
Ireland, was determined in October and November. The 
station was selected in order to eliminate, as far as possible, the 
effect of local attraction at Valentia and Waterville, both of 
which longitude stations are situated between the Atlantic on 
the west and a mountain mass on the east. 
A desire has been expressed by the International Geodetic 
Association for a re-determination of the longitude of Paris— 
Greenwich in view of the discordance in the results found by 
the French and English observers respectively in the two de- 
a 
