$34 General Notes. [August, 
capture of all the positions which at present serve as so many 
slave trade centers is considered now certain. The root of all the- 
nefarious traffic will thus be destroyed, and the destruction of 
these merchants means the end of the trade. 
Owing to the many natural impediments, Col. Gordon is con- 
vinced that the commercial highway of Europe to the rich equa- 
torial districts of Africa does not lie along the Nile but by way 
of the Indian ocean. 
MICROSCOPY.! 
Purity oF Lake Warer.—In a Report on Microscopical Ex- 
aminations of the water from Lake Michigan, as delivered from 
the city hydrants in Chicago, by Mr. B. W. Thomas, in the Third 
Annual Report of the Board of Public Works of that city, it is 
argued that the water for supplying the hydrants is taken from 
too near the shore, although pumped from cribs which are two 
miles out in the lake. After describing the method of obtaining 
organisms by filtering the water through a piece of cotton cloth 
tied in the form of a bag over the end of a faucet, and enume- 
rating the harmless vegetable and animal forms that constitute 
and when once taken into the tunnels and mains they continue to 
multiply, and a few of them can be found in the water supply at 
almost all seasons of the year. 
ti 
supply es 
_ ` This department is edited by Dr. R. H. Warp, Troy, N. Y. 
