670 
PHYSICS: A. McADIE 
hand, a study of the symmetrical profiles of the reef-lagoon structures 
here considered has furnished one more direct indication that the exist- 
ing coral reefs are new upgrowths on platforms, which have been formed 
before, and independently of, the reefs. The volumes of the reefs 
suggest that these began to grow not many thousands of years ago. 
The platforms, on which the reef crowns rest, seem to have been finally 
smoothed, and prepared as foundations, during the Glacial period. 
In any case, the submarine topography of each reef-platform structure 
as a whole and the elementary principles of oceanography together 
declare against the assumption that the forms and spatial relations 
of atoll and barrier reefs are due to the sinking of the earth's crust. 
A NEW THERMOMETER SCALE 
By Alexander McAdie 
BLUE HILL OBSERVATORY. HARVARD UNIVERSITY 
Received by the Academy. October 23. 1916 
In the Physical Review (Vol. VI, No. 6, December, 1915), I urged 
the importance of adopting without further delay, in aerophysics, units 
that have a scientific basis. At Blue Hill Observatory for the past 
two years we have published summaries of air pressure also vapor pres- 
sure in kilobars or force units, temperature in degrees absolute centi- 
grade, and wind velocities in meters per second. Wind direction is 
given in degrees, starting from the West; rainfall in milHmeters and 
evaporation in force units. 
The British Meteorological Ofiice, under the progressive leadership 
of Sir Napier Shaw has published since 1915 results in similar units. 
Unfortunately the European definition of the megadyne atmosphere, 
the bar so-called, is misleading, a more scientific definition being mega- 
bar. The use of the smaller unit does away with the inconsistency of 
defining a millibar as 1000 bars, a self-evident contradiction, and allows 
us to define the bar, the basic unit as the force which would impart to a 
gram an acceleration of 1 cm. per second per second. A kilobar or 1000 
bars becomes then the natural and consistent unit for all measurements 
of pressure in force units. 
With regard to temperature, a concept all important in atmospherics, 
it is regrettable that we have no available method of expressing gain 
or loss of heat in terms of molecular motion. The ordinary mercurial 
thermometer is certainly a crude instrument and so far as thermometer 
scales go, there has been no real improvement since Linnaeus reversed 
the order of the Celsius marking. It will be generally conceded that 
