162 
NATURE 
[JUNE 12, 1902 
The 28-inch Refractor. 
This instrument has been used throughout the year for micro- 
metric measurements of double stars. The total number of 
double stars measured in the year is 382; of these 221 have 
components less than 1/0 apart, and 120 less than 0’’"5. The 
close pairs whose distance apart is less than 1’‘o have been 
measured on the average on three nights each, and the wider 
pairs on an average of two nights. “The wider pairs consist of 
bright stars with a faint companion, of third companions to close 
pairs, and of stars of special interest. 
In addition to the list of most difficult and interesting stars 
measured, it is stated that good series of measures have been 
obtained of « Pegasi, 6 Equulei, 70 Ophiuchi, and ¢ Herculis. 
Capella also has been examined at every favourable opportunity. 
Thompson Equatorial, 
This instrument has been used chiefly for photographing 
Neptune and his satellite, and 52 measurable photographs were 
secured. With the 30-inch reflector long exposed photographs 
of Nova Persei were obtained, but unfortunately, owing to the 
object-glass of the guiding telescope not being quite firm in its 
cell, displacements during exposure occurred. 
Astrographic Equatorial. 
The photography for the Greenwich zone (Dec. + 64° to the 
Pole) having been practically completed, the work during the 
past year was directed to replacing such plates as were found to 
be inferior to the general standard. Four hundred and thirteen 
plates were taken, but of these fifty-seven were for various 
reasons rejected. 
The report contains many details about the measurement of 
the plates, the counting of the number of stars, and various 
other preparations which would occupy too much space, but the 
following table may be given, as a good idea of the magnitude 
of the new work can be at once gathered :— 
Number le b Number | 
Limits of Declination. of Stars umes in | A.G.C. 
|Measured.| A.G.C. 
: Luks eeer H. : ieraeasaers 
64°-65° 8,954 | 1,900 | 1,200 | Helsingfors 
(65°-70° 49,210 | 7,782 | 3,700 | Christiania 
70-75" 50,190 | 5,870 | — Dorpat 
75-77. | 18,100 | 1,856 1,700 | Kazan 
77-78 (oh. to 16h.) | 5,430 613 420 55 
| 
Spectroscopic and Heliographic Observations. 
For the year 1901, Greenwich photographs have been selected 
for measurement on 149 days, and photographs from India and 
Mauritius (filling up gaps in the series) on 210 days, making a 
total of 359 days out of 365 on which photographs are at present 
available. 
The proportion of days upon which the sun was entirely free 
from spots was 80 per cent. for the year 1901, and about the 
same proportion for 1902 to the date of this report. But the 
appearance of two considerable groups this year, and the high 
latitudes of the spots generally, are indications that the actual 
minimum is passed. 
Magnetic Observations. 
The variations of magnetic declination, horizontal force and 
vertical force, and of earth currents, have been registered photo- 
graphically, and accompanying eye observations of absolute 
declination, horizontal jorce, and dip have been made as in 
former years. The regular determinations of magnetic declina- 
tion, horizontal force, and dip have been made with the new 
declinometer, the Gibson deflection instrument, and the Airy 
dip circle mounted in the Magnetic Pavilion. 
The principal results for the magnetic elements for 1901 are 
as follow :— 
Mean declination ... bs «+ 16° 260 West. 
f 4°0082 (in British units). 
‘\.1°8481 (in metric units). 
Mean dip (with 3-inch needles) .... 67° 6’ 5”. 
NO. 1702, VOL. 66] 
Mean horizontal force 
These results depend on observations made in the new 
Magnetic Pavilion, and are free from any disturbing effect of 
iron. 
_ The magnetic disturbances in 1901 have been small and few 
in number. There were no days of great magnetic disturbance 
and § of lesser disturbance. 
Meteorological Observations. 
The registration of atmospheric pressure, temperature of the 
air, and of evaporation, pressure and velocity of the wind, rain- 
fall, sunshine and atmospheric electricity has been continuously 
maintained. 
The mean temperature for the year 1901 was 49°°3, being 
o°*2 below the average for the fifty years 1841-90. 
During the twelve months ending 1902 April 30, the highest 
temperature in the shade (recorded on the open stand in the 
Magnetic Pavilion enclosure) was 87°°9 on July 19. The 
highest temperature recorded in the Stevenson screen in the 
enclosure was 86°'0, and in that in the Observatory grounds 
87°'1 on the same day. 
The lowest temperature of the air recorded in the year was 
143, on February 16. During the winter there were 52 
days on which the temperature fell below 32°, a number slightly 
below the average. 
The low temperature in February is the lowest temperature 
recorded in that month since 1895, when, on February 8, the 
minimum Febiuary temperature 6°°9 occurred. 
The number of hours of bright sunshine recorded during the 
twelve months ending 1902 April 30, by the Campbell-Stokes in- 
strument, was 1519 out of 4457 hours during which the sun was 
above the horizon, so that the mean proportion of sunshine for 
the year was 0°341, constant sunshine being represented by 1. 
The rainfall for the year ending 1902 April 30 was 17°89 
inches, being 6°65 inches less than the average of fifty years. 
The number of rainy days was 116. The rainfall has been less 
than the average in each year since 1894. The total deficiency 
of rainfall for the seven years ending 1901 December 31 
amounts to 23°70 inches. 
The remaining portion of the report deals with the printing 
and distribution of the Greenwich publications, the examination 
of chronometers, time-signals, &c. 
A short reference is made to the re-determination of the 
Greenwich-Paris longitude, and to the expedition which went 
out to Sumatra and Mauritius to observe the total solar eclipse 
of May 18, 1gor. : 
EVIDENCE OF A “ SEICH. 
LOCH. 
WHILE engaged in the survey of Loch Trieg, Inverness- 
shire, on May 22, Dr. T. N. Johnston and Mr. J. Parsons, 
of the British Lakes Survey, observed what appears to be an 
undoubted sezche, z.c. a periodic variation in the level of a lake, 
considered by Prof. Forel, among others, to be due to sudden 
changes in barometric pressure, whilst others, again, consider 
them due to earth-movements. 
The attention of Dr. Johnston was first drawn to the pheno- 
menon by observing that certain small stones near the shore 
were covered and uncovered at regular intervals, the surface of 
the loch being perfectly calm at the time, and had been so 
during the day. 
Ata quarter to 9 p.m., a foot rule was placed vertically in the 
water and the surface level observed at intervals of one minute 
for forty minutes. 
The results obtained confirmed the rougher observation that 
the surface of the water was undergoing slow oscillations. 
The amplitude of the wave proved to be ,°; inch, and the 
period, z.e. the time taken in rising from the lowest to the highest 
level and falling again, averaged 9°5 minutes. 
Despite the smallness of the amplitude compared to that 
noticed on the Lake of Geneva and other lakes, the observers 
had no doubt that the movements were not due to surface ripples. 
Loch Trieg is about six miles long and three-quarters of a mile 
wide, its longer axis lying nearly north and south. The survey 
of the loch is now completed, and a depth of 436 feet has been 
found within two miles of the southern extremity. oe 
Should this variation of level prove to be a true seéche it will 
” ON A SCOTTISH 
