Croll, James, 1821-1890 (physical geologist and Keeper of Maps and Correspondence, Geological Survey of Scotland)

Scope and Contents Letter to Sir Charles Lyell from James Croll concerning the quantity of heat received from the sun between two equinoxes, the effect of Perihelion and Aphelion on the length and strength of summers and winters and the effect of the formation of ice and snow on the levels of heat given off from the earth, 17 April 1866.

Scope and Contents Letter to Sir Charles Lyell from James Croll concerning the temperature of the earth in both winter and summer and how this temperature is affected by the position of the earth in relation to the sun and snow and ice throughout the world, 23 April 1866.