SCIENTIFIC SUMMARY. 
105 
Corrosion of Ships. — Mr. Daft’s proposition to protect the iron by zinc, by 
placing an intervening thickness of felt between these two metals, and which 
plan was approved of by the late Admiralty, has been tried. A trial of its 
efficiency obviously involved a question of time. Sixteen months having 
elapsed since the commencement of this experiment, the sheet of iron pro- 
tected by a sheet of zinc, and a sheet of felt between the two, was raised from 
the action of the sea- water in Portsmouth Harbour, in the presence of the 
visiting Board of Admiralty. The result was satisfactory. The subsequent 
experiment, which brought the two metals in direct contact, was also highly 
satisfactory in its result. 
Hardness of Silver. — Mr. Mathey, assayer at Loda, has shown that in even 
hard silver there is neither tin, lead, nor any other injurious metal. Its 
hardness, he asserts, is due solely to the high temperature at which silver is 
cast. By letting the crucible cool till a slight solid crust is formed on the 
surface of the fused metal, and casting at this moment, a soft silver with a 
brilliant cut is obtained. — Vide Dingier' s Polytechn. Journal. 
Plow to use Nitroglycerine . — In another number we gave a general account 
of the properties of nitroglycerine, and of the mode of employing this explosive 
substance ; but as a recent and exact description has been published by Mr. 
E. Kopp, we translate it for our readers. Suppose, he says, it is desired to de- 
tach a layer of rocks. At a distance of from 2 -5 to 3 metres from the out- 
side, a mine-hole is dug of about 5 to 6 centimetres diameter and 2 to 3 
metres depth. After having cleared this of dirt, water, and sand, 1,500 to 
2,000 grammes of nitroglycerine are introduced, by means of a funnel. A 
small cylinder, of iron, cardboard, or wood, about 4 centimetres in diameter 
and 5 to 6 centimetres in height, is then introduced and filled with ordinary 
powder. This is fixed to a wick or ordinary mine-fuse, which penetrates 
into it to a certain depth, to assure the inflammation of the powder. By 
means of the match on the fuse, the cylinder is lowered ; and by the feel 
the moment can be easily judged at which the cjdinder reaches the sur- 
face of the glycerine. The match being then held firmly, fine sand is run 
into the hole until it is quite full. It is useless to compress or tamp the 
sand. The match is cut a few centimetres above the orifice, and set fire to. 
In eight or ten minutes, the burning of the wick having reached the cylinder, 
the powder inflames. A violent shock ensues, which instantaneously 
explodes the nitroglycerine. The explosion is so sudden that the sand has 
no time to be projected. 
MICBOSCOPY. 
On the Improvement of the Compound Microscope .— In the Microscopical 
Journal for October, Mr. Fred Curtis gives the following remarks on the im- 
provement of the Compound Microscope, as sequel to a contribution of July, 
1863. He observes : u Concave mirrors in place of lenses in the eyepiece, 
so inclined as to reflect the body of rays into the form of a figure of 4, 
would aflord a convenience of manipulation almost irrespective of the di- 
mensions of the instrument. If approved, a mirror as objective also might 
