TRANSACTIONS. 
87 
states the circumstances under which his observations com¬ 
menced. The place of observation is 4 miles S. W. of Edin¬ 
burgh, lat. 55° 55' 20" N., long. 12 1 57 "’5 west of Greenwich, 
at an elevation of 410*5 feet above the mean level of the sea. 
Five observations were made daily of the barometer and at¬ 
tached thermometer, from 8 to 8^ a.m., at 10 a.m., about 
4 p.m., and at 8 and 10 p.m., in order to detect the morning 
and evening maximum and afternoon minimum. The number 
of observations was 4410, which, being reduced to a standard 
hour (10 p.m.), by methods described at length in the paper, 
yielded the following results. 
The maximum of oscillation occurred in spring and summer 
at 8 or a.m. and 10 p.m., in autumn and winter at 10 a.m. 
and 8 p.m. 
Taking these hours, and selecting the actual maxima, the 
amounts of Oscillation are found to be 
Morning. 
Evening. 
Spring . . 
•0213 
•0202 
Summer . . 
*0181 
•0151 
Autumn . . 
*0136 
•0079 
Winter . . 
*0031 
•0031 
After comparing the results of his observations with an ex¬ 
tensive collection of those of other observers in various latitudes, 
Mr. Forbes proceeded to investigate formulae which should ex¬ 
press with the least error the general amount of oscillations in 
different latitudes, at the level of the sea. For this the paper 
itself, which will appear in the Transactions of the Royal 
Society of Edinburgh, must be consulted, as also for various 
indications of the influence which elevation above the sea, the 
season of the year, and the absolute mean temperature of the 
place, have in modifying the amount and period of occurrence 
of the phenomenon. 
The following Extract of a letter from Sir James South 
to Dr. Brewster, dated Observatory, Kensington, Sept. 29 , 
1831, was read by the Secretary. 
“ Should the York Meeting not have terminated its labours, 
and should you think it worth the trouble, I wish you would 
call the attention of any astronomers that may be there, to 
the anomaly which sometimes attends the transits of the 
satellites of Jupiter, over the planet’s face. Generally speak¬ 
ing, the satellite may be seen to glide on the face as a bright 
planetary disc, and remains so till it has proceeded one sixth 
or one eighth of the planet’s diameter. It then becomes in¬ 
visible till it approaches the opposite limb within one sixth or 
