April 19, 1895.] 



SCIENCE. 



425 



Sun's disc. It is, therefore, possible that 

 Mercury may have an undiscovered satellite 

 200 miles in diameter. If so, and the 

 satellite should be as far from Mercury as 

 the moon is from the earth, it would take 

 1.50 days to make one complete revolution 

 around the planet, or nearlj- twice as long 

 as it takes Mercury to revolve about the 

 aun. Such a satellite would have suflicient 

 mass to cause Mercury to revolve in a 



secondary orbit 1-50 miles in diameter, 

 which would be a measurable quantity. 

 E. S. Wheeler. 

 Sault Ste. Marie, Mich. 



TJIE DISTRIBUTION OF THE BLO W-G UN. 



The blow-gun is one of the most remark- 



al)le savage devices in which compressed air 



is used as a motive force. Primarily, the 



blow-gun is a simple tube of cane, smoothly 



