Instrument for Measuring Water, &c. 199 
phosphoric acid, and not merely the oxide of Uranium and 
eopper combined with water. ' 
_ 25. Prussian travellers —The Prussian naturalists, Drs. 
Ebrenberg and Hemprich, in their tour in the interior of 
Northern Africa, arrived safely at the celebrated Dongola, 
the capital of Nubia, on the 15th of February. These zea- 
lous collectors have sent six remittances to Berlin, and have 
again accumulated more than they can pack in ‘twenty 
chests. Their collection consists of mammalia, birds, am- 
phibia, insects, plants, and what are more rare, fishes and 
insects of the Nile. 
26. An Electro-Magnetic Apparatus of extraordinary 
dimensions has been constructed at the London Institution, 
by W. H. Pepys, Esq. F. R. S. It consists of two plates, 
the one of copper, and the other of zinc, each two feet wide, 
and fifty feet long, giving a total surface of two hundred 
square feet. These plates are wrapt or coiled round a com- 
Mon center, and are prevented from contact with each other 
by the interposition of three cords of hairline, and also of 
notched slips of wood placed at intervals. Iwo con- 
ductors of copper wire, nearly three fourths of an inch in 
diameter, are attached, one to the zinc, and the other to the 
eopper plate. In order that so large a mass may be readily 
employed for experiment, the apparatus is suspended by 
means of pulleys and a counterpoise, and so let down into a 
tub of acid, or, when not in use, into one of water. It re- 
quires fifty five gallons of fluid. ¥: 
his instrument exhibits very powerful magnetic effects : 
When the contact was made, a change in the direction of 
compass needles was produced, at the distance of five feet; 
steel bars enclosed in cylinders of glass, with a spiral of 
Wire round them, were rendered magnetic, and cd om 
Suspended together; when the contact was br he 
bars fell, but ite éf thea was immediately taken up again 
®n restoring the contact, though it weighed above dat eal 
e electric intensity of the apparatus Is very slight i it has 
Rot any decomposing action, and will not make a spark Wi 
eharcoal, nor will it deflagrate the metals. 
27. Instrument for measuring the compression of ma- 
PLM ar fu ple uses a very simple instrament for 
