In January of 1943, the Civil Aeronautics Administration (of the Dept of Commerce) published the very authoritative METEOROLOGY FOR PILOTS. It was authored by B C Haynes, senior meteorologist for the U.S. Weather Bureau (CAB bulletin no. 25)
Therein it states, on pg 72, that the DRY ADIABATIC LAPSE RATE of temperature with altitude is 5.5 deg F / 1000 feet for the ideal dry adiabatic model of the atmosphere at standard sea level temperature (68 F) and pressure which then, just the same as today, was considered to be 29.92 inches Hg.
It cannot be overstressed that the dry adiabatic lapse rate for temperature I gave you is an average drawn from hundreds of thousands of observations taken from all over the globe over the past century...it is an AVERAGE. It goes on to state in this book that the temperature lapse rate is generally uniform up to about 35,000' and then the temperature remains constant (zero lapse rate) or may even increase from there on up for a distance and then begins decreasing again.
The reason they use the word "adiabatic" is that it is based on an "adiabatic" model of the earth's atmosphere....the earliest barometers were based on the "isothermal" model which assumed a constant temperature from sea level on up. The adiabatic assumes that as a given volume of air rises, it loses internal energy by doing the work of expanding against the decreasing pressure as it rises. This is much closer to reality than the isothermal and actually results in an equation that says that the atmosphere comes to an end at 102,000 feet.
In any event, some of the confusion with lapse rates is probably due to the fact that the figure of 5.5 is for the DRY rate at STP while any amount of moisture results in what they call the "wet adiabatic lapse rate" and is lower----2.5 or 3 degs F per 1000 for example.
