396 proceedings: philosophical society 



from three normal equations which are readily written by the star 

 point method after the data have been properly charted. The results 

 are remarkably accurate. The studies show that the minimum tem- 

 perature can be closely predicted n the orchard at a considerable distance 

 from the observing station; that the hygrometric observations made at 

 noon may be used quite as well in some instances as those made in the 

 evening, and that the equation will sometimes apply as well to cloudy 

 as to clear nights. 



By using the depression of the dewpoint instead of the relative 

 humidity in correlating with the variation of the minimum temperature 

 from the dewpoint there is, in some instances, an even closer relation 

 shown. In this case a straight line from the equation v = x -\- yd 

 fits the data fully 83 per cent of the time. In this equation d is the 

 depression of the dewpoint, v is the variation of the minimum from the 

 dewpoint, and x and y the two unknowns. 



Discussion: Mr. Abbot exhibited a slide indicating a relation be- 

 tween solar-constant variations and minimum temperatures. 



Mr. Brooks spoke of the effect of snow cover in lowering the minimum 

 temperatures. 



Replying to question by Mr. Sosman, Mr. Smith stated that the 

 protection afforded to orchards by the use of heating pots was not due 

 to the smudge produced but to an actual increase of from 4 to 8 degrees 

 in the temperature of the air. 



Mr. Humphreys showed that the artificially heated air in an orchard 

 does not rise far on account of a marked temperature inversion. 



The second paper was by Mr. Charles F. Brooks on Clouds and 

 their significance,- and was also illustrated by lantern slides. 



When closely observed, clouds are remarkable indices of atmos- 

 pheric processes and movements. Their forms and motions may be 

 used not onl}- directly in determining what general winds and turbulence 

 exist at different levels, but also in surmising the vertical distribution 

 of temperature and humidity. Here without the expense of apparatus 

 are the means for discerning what is happening in he atmosphere up to 

 great heights, and, therefore, the means for determining the causes of 

 certain features of our weather, and for forecasting local changes. 

 Also, the effect of cloudiness on the temperature and humidity of the 

 lower air is not to be overlooked. 



The cloud transformations and movements during the passage of a 

 strong low-pressure area in winter give a fairly clear picture of the 

 internal dynamics of such a storm. As the low approaches, a relatively 

 warm southerly wind enters like a sideways-moving wedge over the cold 

 surface air, and under the westerly upper wind. The lower surface 

 of contact is frequently marked by stratus clouds formed by mixture, 

 and the upper by alto cumulus clouds formed by thermal convection 

 due to the warmth of the southerly wind relative to that above. Later, 

 the warm wind reaches the earth's surface. The lines of appreciable 



* ThispaperwaspublishedintheMonthly Weather Review, 48: 26-28, Jan., 1920. 



