SOLAR LIGHT AND HEAT: 



THE SOURCE AND THE SUPPLY. 



GRAVITATION: 



WITH EXPLANATIONS OF 



PLANETARY AND MOLECULAR 

 FORCES. 



BY 



ZACHARIAH ALLEN, LL.D. 



NEW YORK: 

 D. APPLETON & CO. 



LONDON: D. APPLETON & CO., 16 LITTLE BRITAIN. 

 1879. 



