wien: recent theories of heat and radiation 273 



points of Babinet and Arago, respectively, were materially in- 

 creased when the sun was above the horizon. With the sun below 

 the horizon the increase was slight, and in some cases there was 

 even a decrease. 



These effects upon sky light polarization are in every way simi- 

 lar to the effects observed in 1903 after the eruption of Mount 

 Pelee n 1902. 



The effect of decreased solar radiation intensities upon air tem- 

 peratures. In the Bulletin of the Mount Weather Observatory 

 3 : 1 1 1 , a diagram is given which shows that diminished solar radia- 

 tion intensities comparable with those of 1912 occurred in 1884-86, 

 1891, and 1903. Each of these periods was accompanied and fol- 

 lowed by temperatures below the norma] in the United States. 

 While the minus temperature departures were not greater than 

 have occurred in other years, they persisted for a greater length 

 of time. 



It will be of interest to observe if the present depression in the 

 solar radiation intensity curve is also followed by a long continued 

 cold period in the United States. 



PHYSICS. — Recent theories of heat and radiation.^ W. Wien, 

 Professor of Physics, University of Wiirzburg. 



In a series of lectures at Columbia University, I am treating 

 several problems which are of peculiar interest to modern physics 

 but which already present grave theoretical difficulties. The 

 hypothesis of elements of energy or quanta, as given by Planck 

 and expressed in the well known formula, is indispensable in the 

 statistical treatment of molecular physics. It contains something, 

 however, which lies beyond the commonly accepted system of 

 ph.ysical theory. The difficulty in all these problems lies in the 

 fact that one must constantly make use of relations, which are 

 difficult to determine, between the theory of quanta and the older 

 classical theory. 



It is impossible as yet to say to what extent the theory of quanta 

 may be applied. Thus far, its application has been confined to 



^ An address delivered before the Washington Academy of Sciences on April 23, 

 1913. 



