129 
The mean proportion of advance which the wind makes 
with the sun’s course on the East side of the compass, as re- 
sults from the foregoing table, is nearly twice as much as such 
advance is on the West side, for the mean proportion of the 
advance on the East side is 2 - 28, whilst on the West side it 
is only 1*2] . And it seems to show that the progress of the 
wind round the compass in the direction of the sun’s course 
is retarded chiefly by westerly winds. 
I may also state that the horizontal movement of the air 
has a maximum at a point similar to the maximum of wind 
frequency and wind oscillation, for on reducing and refer- 
ring the horizontal movement of the air for 1869 to the four 
cardinal points, I find the mean values to be as follows : — 
Cardinal points N E S W 
Meanliorizontalmove- ) 
ment of the air ... j 91 99 117 117 
Thus the maximum lies between the South and the West. 
“ On Black Bulb Solar Radiation Thermometers exposed 
in Various Media,” by G. V. Vernon, F.R.A.S., F.M.S. 
Being desirous to make some comparisons of the readings 
of black bulb thermometers exposed in various media, I got 
Messrs. Negretti and Zambra to make me a set of three 
thermometers, in addition to the ordinary black bulb maxi- 
mum in vacuo. 
The glass tubes containing the thermometers were filled 
with hydrogen gas, carbonic acid gas, and atmospheric air, 
at 32° F. ; the latter thermometer being described in the 
tables as filled with compressed air. The instruments were 
all alike, the glass tube enclosing them being of equal thick- 
ness. The thermometers were all compared with the 
Greenwich standard, and require no index error correction. 
The observations were made in the years 1861 to 1865, 
and the period embraced was just four years. Since the 
latter year the observations have been discontinued, but the 
thermometers remain in the same position they were 
originally placed in. 
