136 Bibliographical Notices. 
A. R. Wallace. The change depending on the position of the peri- 
helion is completed in about 21,000 years ; while that depending on 
the eccentricity takes ae more ae for its course. The eccen- 
tricity may have been ++, instead of ,1,, as at present; but astro- 
nomers are unable to say when the maximum eccentricity took 
place. An alternate glaciation of the northern and southern hemi- 
spheres every 21,000 years has been hence deduced by Adhemar, 
Croll, and Murphy, the glaciation being more or less severe as the 
eccentricity in the perihelion period was greater or less. Croll 
places the glaciation of a hemisphere when its winter solstice was in 
aphelion, and Murphy places the glaciation of a hemisphere when 
its winter solstice was in perihelion. 
Dr. Haughton thus expresses this secular inequality in climate :— 
“The mean annual temperature of any place varies as the eccen- 
tricity of the earth’s orbit and as the range of temperature from 
summer to winter jointly.” He remarks, “ Of these two factors of 
climate, viz. eccentricity and range of temperature, the first is astro- 
nomical, and the second terrestrial, depending on distribution of land 
and water, on ocean-currents and prevailing winds ;” and he adds, 
“if we suppose the terrestrial factor to be the same while the 
eccentricity attains its maximum, the greatest possible change in 
mean annual temperature for any place on the earth’s surface turns 
out to be less than 5° F.; and, in order to produce a sensible effect 
upon climate, we must suppose that the annual range (terrestrial 
factor) must vary also by variation in the distribution of land and 
water.” Taking several examples of the present annual range of 
temperature at places where Miocene plant-beds exist, and calcu- 
lating what the annual range must have been for those fossils, and 
allowing for any fairly possible distribution of land and water, Dr. 
Haughton shows that ‘ change of eccentricity of the earth’s orbit is 
not sufficient to account for former geological climates.” 
Vi Geographical Distribution of hoe ind Water. This is shown 
in the foregoing discussion to be inadequate as a cause for the past 
changes in geological climate; and Dr. Haughton indicates that 
Mr. Wallace strongly supports the view of the relative persistence 
of the continental and oceanic areas, and that the present differ- 
ences of the northern and southern hemispheres have existed from 
the beginning and are due to an eccentric position of the earth’s 
centre of gravity. The southern hemisphere has thus been always 
more under water than the northern, and always will be. It is 
warmer than the northern, because it receives three tepid currents 
of equatorial water instead of one ; and continental climates are and 
always have been characteristic of the northern, and insular climates 
of the southern hemisphere. 
VI. Alterations in Sun-heat. This is accepted by Dr. Haughton 
as the most probable of all causes of change in geological climate, 
whether cold or hot. He thinks “ that the Glacial period or periods 
were non-periodic, that they affected both hemispheres simulta- 
neously, and depended altogether on physical changes in the sun 
itself, and not on the physical or astronomical conditions of the 
eee a hme 
gernens 
