Instrument for Measuring Watery ^c. 195 



phosphoric acid, and not merely the oxide of Uranium and 

 copper combined with water. 



25. Prussian travellers — The Prussian naturalists, Drs. 

 Ehrenberg and Hemprich, in their tour in the interior of 

 Northern Africa, arrived safely at the celebrated Dongola, 

 the capital of Nubia, on the 1 5th 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 coniact with each other 

 by the interposition of three cords of hair line, and also of 

 notched slips of wood placed at intervals. Two con- 

 ductors of copper wire, nearly three fourths of an inch in 

 diameter, are aitiiched. one to the zinc, and the other to the 

 copper plate. In order that so large a mass may be readily 

 employed for experiment, the apparatus is suspended by 

 means of pulleys and a count'^rpoise, 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. 



This 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 severalwere 

 suspended together ; v;rhen the contact was broken, the 

 bars fell, but one of them was immediately taken up again 

 on restoring the contact, though it weighed above 270 grains. 

 The electric intensity of the apparatus is very slight ; it has 

 not any decomposing action, and will not make a spark with 

 charcoal, nor will it deflagrate the metals. 



27. Instrument for measuring the compression of wa- 

 ter. — Professor Oersted uses a very simple instrument for 



