i9i?.] 



Night Frosts in Spring. 



935 



it is moist or the dew point and wet bulb temperatures are 

 near the dry. 



Practical Hints in Forecasting Frosts. — From what has 

 been said above, it will be gathered that anyone who is in- 

 terested in protecting his crops from night frosts, and, there- 

 fore, wishes to know beforehand when frosts are likely to 

 occur, will do well to study : — 



(1) The peculiarities of his locality to know whether 

 from being in a cup or valley it is specially liable to 

 frosts on calm nights. 



(2) The daily charts, with or without forecasts by tele- 

 graph, in order that he may recognise the meteorological 

 conditions in which the weather is likely to become cold 

 and calm. 



(3) The readings of the dry and wet bulb thermometers 

 so that he may recognise the occasions when ground 

 night frosts are likely to be severe on account of the 

 dryness of the air. 



Protection against expected Frosts.* — The best method of 

 protection for young plants against night frosts is to cover 

 them up and thereby prevent first of all the loss of heat, and 

 secondly the access of cold air. 



Other means of protection have been tried. Saturation of 

 the ground in which the plants are growing with water is 

 resorted to in fruit plantations in California. Possibly the 

 evaporation of the water is in itself a protection, as it pro- 

 motes the formation of a mist over the land to be protected, 

 but the warmth of the water itself no doubt also acts to 

 prevent the air just above it being cooled as much as it 

 would have been if the ground had been dry. On the other 

 hand, Continental writers point out that delicate plants are 

 more sensitive to the effects of frost when their cells are fully 

 charged with water than when they are in a dry condition, 

 and the adoption of this method, though mitigating- the in- 

 tensity of frost, may therefore lead to increased damage to 

 the crop. Possibly differences in the character of the crops 

 to be protected, more particularly the heights of the sensitive 

 parts above the ground, may account for the apparent differ- 



* For an account of methods other than those mentioned in these Meteorological 

 Office Notes, see the previous numbers of the journal already referred to. 



