244 Correspondence . [April, 
steam away with the fertilising material to depots in the course 
of the river, where the material could be applied, direCtly or after 
precipitation, to the purposes of agriculture.” 
It may be instructive to examine what tonnage would be re- 
quired thus to convey away the sewage of a large town situate 
on a navigable river. The daily dry-weather flow of sewage 
from the town in question is estimated at a minimum of 8,000,000 
gallons = 80,000,000 lbs. weight, or, in round numbers, 
35,000 tons. To convey this mass of liquid away we should re- 
quire the constant service of 175 barges, each of 200 tons capa- 
city, or from fourteen to fifteen every hour per working day of 
twelve hours. Let your readers imagine the outlay of building 
this fleet, and the daily working cost in wear and tear, interest, 
fuel, and wages, and then refledl that the ordinary expenses of 
the disposal of sewage, whether by irrigation or precipitation, 
would have to be superadded. — I am, &c., 
Beggiatoa alba. 
INFLUENCE OF WHITE OBJECTS. 
To the Editor of the Journal of Science . 
Sir, — Can any or your readers explain why a white cloth, a 
sheet of paper, or other white objeCt, especially if in motion, has 
such a repulsive effeCt upon birds, wild or tame ? Upon insedls 
they seem to have a powerfully attractive influence, as anyone 
may observe who lays down a white cloth in a field or wood, and 
awaits the result. — I am, &c., 
P. 
