18 THE MICROSCOPE. Feb. 
are forming, winds, lighter or stronger prevail, and the 
formation of irregular crystals on the side towards the 
storm is thus promoted. 
Dr. Hellmann’s work is iliustrated by photo-micro- 
graphs by Dr. R. Neuhaus. They are enlarged from 
ten to thirty times and are eminently realistic. It is 
from these that our figures are sopied. It is well to 
notice the irregularties in the length of arms and in the 
formation of the arms. 
To examine snow crystals the work is better done in 
the open, as they evaporate rapidly in a low temperature, 
