PRESIDENTIAL ADDRESS. 25 
sphere. Mr. J. Sebelien (Phil. Mag., March 1905), after 
briefly reviewing the work of Halley and other authorities, 
brings together some values obtained by Bunsen and Roscoe 
into tabular form, showing the extent to which diffused 
daylight tends to equalise the numbers for the total quantity 
of light at the different latitudes. It is further shown that 
while at the equator the effect of the direct insolation on 
the said day has double the value of the daily effect of the 
diffused daylight these numbers will become equal in the 
neighbourhood of 49° north latitude, the further we get 
towards the north or south (if in the southern hemisphere) 
the more diffuseddaylight will dominate. Also it is shown 
that the preference conferred upon the northern and southern 
latitudes with regard to their actinic illumination at the 
equinoxes will increase with the declination of the sun, 
and reach its maximum value at the summer solstice. 
Then using the formulze of Bunsen and Roscoe, Mr. 
Sebelien has calculated the quantity of actinic light which 
on a midsummer day falls upon an horizontal element of 
surface from sunrise to sunset for every tenth degree of 
latitude ; the resulting values are plotted graphically. 
Meteorites.—H. KH. Wimperis states that it is probable 
that the velocities of meteorites are by the resistance of 
the atmosphere changed by a fractional part of the 
velocity, which fraction is independent of the velocity of 
approach; that the superior limit for incandescence is 
about 150 miles above the earth’s surface, and that no 
iron nfeteor, the original weight of which was less than 
10 to 20lbs, reaches the earth’s surface, and that when a 
meteor does so, the temperature of its centre is not in 
general above that of liquid air (assuming the temperature 
of space to be absolute zero). 
Zodiacal Light.—A. H. Hansky gives details of observ- 
ations made on the evenings of September 21-22, 1904, 
at the observatory on the summit of Mount Blanc :— 
