MICROSCOPIC ILLUSTRATIONS. 63 



organisms, a few Confervce, and about thirty 

 kinds of infusoria. Thus a glance with the 

 Microscope solved a riddle which had perplexed 

 Europe's philosophers for more than a century. 

 Murray tells us, in his Handbook for Swit- 

 zerland, that red snow is common among the 

 high Alps. Rose-coloured snoiv fell to the 

 depth of six feet in the Tyrol in 1808. Green 

 snow has been collected in Spitzbergen. Sir 

 John Koss collected red snow upon a range of 

 Arctic hills 800 feet above the level of the sea. 

 Black rain fell in Ireland in April 1849, over a 

 surface of 700 square miles. Humboldt observed 

 red hail near Bogota. 



4. Again the Microscope unties the knot. It 

 has been found that in such cases a minute 

 red, sometimes green, coloured plant, called 

 the Protococcus, penetrated and pervaded the 

 snow, and so imparted the colouring. In other 

 cases, vast numbers of microscopic animals, 

 floating in the air, had descended with rain or 

 snow, and so produced the phenomena. 



5. In a work entitled Passat-Staub und Blut- 

 Regen, Ehrenberg has investigated this whole 

 subject very carefully, and records the occur- 



