IIutUjIitOit—Erccntl'if'tty of tilt: Etl I'tli \v Oi'hh 



Art. L.— On Eccentricity and l\ . the Earth's 



Orbit as a cause of change of Climate. From the Presidential 

 Address before the Geological Society of Dublin, by Rev. 

 Samuel IIaughton, in February, 1882. 



Another astronomical cause of change in geological climate 

 was proposed by Adhemar, and afterward worked out more 

 fully by Croll, J. Murphy and Wallace. 



This is tlm secular variation in climate depending on the 

 eccentricity and perihelion longitude of the earth's orbit. 



The change depending on the position of the perihelion is 

 completed in about 21,000 years; while that depending on the 

 eccentricity requires much more time to pass through its course. 

 In fact, astronomers have proved that the eccentricity of the 

 earth's orbit may have been -J^th instead of -fat\\, as at present; 

 but are unable to say how long ago the maximum eccentricity 



Adhemar, Croll and J. Murphy deduce from this astronomi- 

 cal cause the alternate glaciation'of the northern and southern 

 hemispheres every 21.000 years, which glaciation is more or 

 less severe in proportion as the eccentricity during the perihe- 

 lion period is greater or less. Mr. Croll, however, places the 

 glaciation of a hemisphere in the time when its winter solstice 

 is in aphelion ; whereas Mr. J. Murphy places the glaciation of 

 a hemisphere in the time when its winter solstice is in peri- 

 helion. 



pressed without the use of mathematical i 



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. -\ 



Of these two factors of climate, viz: eccentricity and range 

 of temperature, the first is astronomical and the second terres- 

 trial, depending on distribution of land and water, on ocean 

 currents and prevailing winds. 



If we suppose the terrestrial factor to be the same, while the 

 eccentricity attain- its maximum, the greatest possible change 

 in mean annual temperature for any place on the earth's sur- 

 face 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 dis- 



