224 HORTICULTURIST'S RULE-BOOK. 



between the readings of the dry and wet bulb is entered in 

 the horizontal line at the top, from 1 to 13. To find the 

 temperature of dew-point at any observation, find in left-hand 

 column the temperature of dry-bulb, then follow the horizontal 

 line opposite that figure till you reach the perpendicular col- 

 umn under the difference between dry and wet bulb readings, 

 and the figures at the meeting of these two columns will give 

 the temperature of dew-point. For example, suppose the dry- 

 bulb stands at 65 and wet-bulb at 55, the difference is 10. 

 Pass across the page in the line of 65 till you intersect the 

 vertical column under 10 and you read 47, which is dew-point 

 under these conditions. If the dew-point is 10 or more above 

 frost-point (32 Fahrenheit), there is no danger of killing 

 frost; but if the dew-point is less than 10 above 32, danger 

 may be apprehended. If a line is drawn from the intersection 

 of 43 1 and 67 13, of the table, this may be called the 

 danger line, and all dew-point temperatures below this line 

 indicate danger of frost, and are printed in italics. This mar- 

 gin of 10 is taken because the temperature on a still night 

 will sink a few degrees below the first dew-point, and the 

 temperature of the air at 5 feet above the ground is several 

 degrees above that at ground level. For these reasons com- 

 bined a margin of 10 may be safely assumed as the limit of 

 safety. 



To Protect Plants from Light Frosts. 1. Make a smudge 

 in the garden or vineyard at night when the frost is expected. 

 Rubbish or litter and tar make the best smudge. 2. Syringe 

 the plants thoroughly at night-fall. 



" If the farmer is forewarned of the approach of a still frost, 

 he may do something to avert the calamity. The conservative 

 influence of watery vapor is the most hopeful means of pro- 

 tection, and sometimes trivial causes of this class will produce 

 surprising results. The old plan of ' a tub of water under the 

 fruit tree, and a rope reaching from the tub into the branches,' 

 may serve a useful purpose. The evaporation from the water 

 in the tub and of the water carried up by capillary action in 

 the rope may spread the protecting folds of the water blanket 



