102 ON THE POSSIBILITY OF PREVENTING DAMAGES BY FROST. 



Fertilizers, applied to the soil without jiulgment, medicines 

 given to a patient with no discrimination, may cause serious 

 injuries. The using of frost preventives must also be based on 

 knowledge and experience. 



As, however, not only the climate generally in a country, 

 but also local conditions influence the phenomena connected 

 with the frost, it is impossible to lay down a general rule as to 

 the methods for avoiding frost. My own experience of frost in 

 Queensland is far too limited to allow me to speak of it with 

 regard to this country ; but my experience gathered in other 

 countries will enable me to offer some suggestions as to the frost 

 phenomena in general and the causes of its appearance. I 

 will also give a short summary of the results of the frost investi- 

 gations made in Sweden and Finland, the two coldest countries 

 in the world where agriculture is carried on, the countries where 

 Jack Frost is the worst foe of the agriculturist. 



My short notes are chiefly founded on the excellent works 

 of Professor Selim Lemstrom, of Helsingfors, Finland, whose 

 researches on the Polar light and night frosts, have made his 

 name familiar to the scientific world. Through the courtesy of 

 the present chairman of the Finnish Society of Science, Dr. Th. 

 Homen, Professor of Applied Physics at the University of 

 Helsingfors, I recently received some of his latest works on the 

 frost question, and they will enable me to discuss some of the 

 latest results of experiments made. 



THE CAUSES OF NIGHT-FROSTS. 



Since the investigations of Wells in Surrey, England, in 

 the beginning of last century, it has been known that the 

 principal cause of night-frosts is the radiation of heat from 

 the surface of the earth and from the substances that are upon 

 it. Every body, the temperature of which is higher than that 

 of its surroundings, suffers a constant loss of heat until temper- 

 ature is the same everywhere. 



On a summer day the surface of the earth is heated by the 

 sun, i.e., the earth obtains a surplusage of heat, which in 

 various kinds of surfaces is different, and which penetrates more 

 or less deeply into the ground, depending on its heat conducting 

 power. When the sun's effect has ceased, the earth and the 

 objects on it begin to give out heat through radiation into 

 space. The temperature of the earth sinks at first very rapidly, 

 being higher in comparison with that of space, but later more 

 slowly, depending on its surroundings. The radiated heat has 



